An 80 year old female had a history of chronic iron deficiency anemia with unknown cause and comorbidities included hypothyroidism, congestive heart failure (CHF), severe aortic stenosis and COPD. The patient presented at the ED with initial presentation with increasing shortness of breast, NYHA class 3-4. She was admitted to the hospital for further treatment for CHF, as well hyperventilation, sleep apnea and COPD. Her serum iron and iron saturation were tested and results were 2 umol/L (reference range for iron: 10-29 umol/L) and 7% (reference range: 14-51%), respectively. Part of her investigations included a qualitative fecal test to screen for gastrointestinal bleeding. The immunochemical fecal occult blood test was performed using a CLIA waived Hema Screen SpecificTM POCT test (Immunostics, Inc, USA) in the hospital lab. Hema Screen Specific test is a qualitative, sandwich dye conjugated immunoassay that uses a combination of monoclonal and polyclonal antibodies to detect the globin component of hemoglobin in the fecal samples. The manufacture recommended using Hema Screen Specific test in routine physical examines, hospital monitoring of bleeding in patients and for screening for colorectal cancer or gastrointestinal bleeding for any source (statement from the product package insert).
The specimen submitted to the lab was markedly red (Image 1), yet Hema screen test returned a negative result. Since this device is designed to detect occult blood in fecal samples, a prozone effect was suspected, as the stool appeared to contain overt hemorrhage. The specimen was reanalyzed with serial dilutions by a factor of 5, 10, and at 100 × dilution. The FIT result became clearly positive for blood (Image 2). The patient received a colonoscopy, which revealed internal hemorrhoids, severe diverticulosis in the left colon, as well as multiple angiodysplastic lesions. One such lesion was in the ascending colon and was actively bleeding at the time of colonoscopy. The others, which were not bleeding, were distributed in the proximal ascending colon, hepatic flexure, and proximal transverse colon. All angiodysplastic lesions were treated with argon plasma coagulation.
Moreover, we have tested the device with another bloody fecal sample during the initial evaluation. When an appropriate dilution factor was used, the prozone effect begins to lose its interference as show in Image 3.
The prozone effect (or Hook effect) has long been appreciated as a source of interference in immunoassays.1 It typically occurs in sandwich assays, of which the FIT test is an example.2 When the concentration of the analyte is excessively high, it oversaturates the capture and detection antibodies in favor of forming single antibody:analyte complexes, rather than sandwiches. This results in a false negative result where the assay is unable to detect the analyte. The solution to the prozone effect is serial dilution to lower the concentration of the analyte.
The FIT test is designed to detect microscopic amounts of blood, hence its function in screening for fecal occult blood. A number of hospital labs use this test in an acute care setting to screening bleeding in patients. However, its capacity is oversaturated in specimens containing overt hemorrhage, as in our patient. In these cases it is nevertheless important to prove that the red color of the specimen is truly due to blood, as bright red stool can be caused by a wide range of dietary factors. Some examples are red food coloring, beets, cranberries, and tomato juice.3 If these possibilities are not ruled out, the patient may become subject to the risks of unnecessary endoscopy. Serial dilution of the specimen is extremely useful in this type of situation.
Dasgupta A, Wahed A. Clinical Chemistry, Immunology and Laboratory Quality Control: A Comprehensive Review for Board Preparation, Certification and Clinical Practice. Amsterdam: Elsevier; 2014. 2.11.
Allison JE, Fraser CG, Halloran SP, Young GP. Population Screening for Colorectal Cancer Means Getting FIT: The Past, Present, and Future of Colorectal Cancer Screening Using the Fecal Immunochemical Test for Hemoglobin (FIT). Gut and Liver. 2014 Mar;8(2):117-30. https://doi.org/10.5009/gnl.2014.8.2.117
-Hao Li, MD is a currently a first year anatomical pathological resident at Western University, London ON, Canada. Prior to be a pathology resident, he was a neurosurgery resident at the University of Saskatchewan, Saskatoon SK, Canada. When he was at the University of Saskatchewan, he spent his third year primarily in neuropathology, with also some general anatomical pathology and clinical pathology. Through these experiences, he has come to realize that his passion and calling lay more in pathology than in surgery. He has successfully transferred into pathology, and started a new residency in anatomical pathology in July 2019. Having a background in the clinical neurosciences, he hopes to eventually pursue a fellowship in neuropathology, and possess the skill set to practice both anatomical pathology and neuropathology.
Vitamin D is one of the most commonly ordered laboratory
tests in the primary care setting, as well as one of the most widely used forms
of dietary supplementation today. While the rationale underlying vitamin D
testing and supplementation for deficiency may seem straightforward, in
actuality, the metabolism and physiologic functions of vitamin D in the body
are quite nuanced and complex, and there remains significant controversy
surrounding the appropriate utilization of vitamin D measurement and clinical
interpretation of vitamin D test results. In this post, let’s review the basic
principles of vitamin D metabolism, its function and mechanisms of regulation
in the human body, methods of measurement in the laboratory, and ramifications
of vitamin D values on clinical decision-making and management.
Vitamin D Metabolism
Vitamin D is a fat-soluble vitamin and encompasses a group
of compounds, all containing a four-ring steroid backbone. The two main forms
of vitamin D utilized by humans are vitamin D3 (cholecalciferol) and
vitamin D2 (ergocalciferol). Vitamin D3 is primarily
synthesized in the skin from 7-dehydrocholesterol in the presence of sunlight
(UVB rays), while vitamin D2 is synthesized in plants from
ergosterol and is used to fortify many foods (milk, bread, cereal, etc.).1
Once synthesized in the skin or ingested from the
gastrointestinal tract, both vitamin D2 and vitamin D3
travel in the bloodstream (bound to vitamin D-binding protein) to the liver,
where both are converted to 25-hydroxyvitamin D [25(OH)D,
calcidiol/calcifediol] by the action of 25-hydroxylase.1,2 While 25(OH)D
has only limited biologic activity, it has a very long half-life (2-3 weeks)
and is therefore the primary form of vitamin D found in the blood.1 Notably,
the half-life of 25(OH)D2 is shorter than that of 25(OH)D3
(possibly due to lower affinity to vitamin D-binding protein) and therefore it
is present in significantly lower concentrations than 25(OH)3 in the blood.3
25(OH)D is then further converted to 1,25-dihydroxyvitamin D
[1,25(OH)2, calcitriol] via the action of 1-α-hydroxylase primarily in the
kidney.1 In contrast to 25(OH)D, 1,25(OH)2D is the
biologically active form of vitamin D, but it has a much shorter half-life (5-8
hours) and therefore has much lower circulating levels in the blood.1
25(OH)D may alternatively be converted to 24,25-dihydroxyvitamin D [24,25(OH)2D]
also in the kidney. 24,25(OH)2D is an inactive metabolite and thus
serves as an end-product in this degradation-type pathway of 25(OH)D.1,4
Vitamin D Physiology
The overall effect of vitamin D in the body is to increase
calcium and phosphate levels in the blood. Via binding of 1,25(OH)2D
to nuclear receptors within cells, it acts at three main sites: 1) the
intestine, where it increases calcium and phosphate absorption, 2) the bones,
where it increases calcium resorption by promoting osteoclast maturation, and
3) the kidney, where it increases calcium reabsorption by enhancing the effects
of parathyroid hormone (PTH) on the distal convoluted tubule.1
Conversion of 25(OH)D to 1,25(OH)2D by
1-alpha-hydroxylase is tightly regulated by calcium, phosphate, and PTH
concentrations in the body. Decreased calcium or phosphate levels, or increased
PTH levels in the blood (most commonly resulting from a fall in calcium) will
activity and lead to increased production of 1,25(OH)2D, while
increased calcium or phosphate levels or decreased PTH levels will suppress 1-α-hydroxylase
activity and thus lead to decreased production of 1,25(OH)2D.1,2
From a clinical perspective on vitamin D physiology, there
are numerous causes of abnormal vitamin D levels in the body. Here are some
common causes of low vitamin D levels:
Inadequate intake of vitamin D (whether from
diet, inadequate sunlight, or malabsorption)
Decreased PTH (hypoparathyroidism,
hyperphosphatemia, hypercalcemia of malignancy)
End-organ resistance to PTH
Decreased 1-α-hydroxylase activity (renal
failure, vitamin D-dependent rickets type 1)5
Conversely, causes of high vitamin D levels are listed
Excessive intake of vitamin D (usually from
Increased PTH (primary hyperparathyroidism)
Increased extrarenal 1-α-hydroxylase activity (seen in
granulomatous diseases such as sarcoidosis, as well as some lymphomas)
End-organ resistance to vitamin D (vitamin
D-dependent rickets type 2)5
Vitamin D Measurement
in the Laboratory
25(OH)D is the most commonly measured vitamin D metabolite
in laboratory assays, since (as mentioned above) it has a longer half-life and
a larger concentration in the blood compared to 1,25(OH)2D. In
addition, its concentration does not fluctuate as significantly as that of 1,25(OH)2D,
since its production from 25-hydroxylase in the liver is not so tightly
regulated as 1-α-hydroxylase activity in the kidney.1,6
Nevertheless, 1,25(OH)2D measurement is indicated in a few specific
clinical circumstances, including workups for idiopathic hypercalcemia and
bone/mineral disorders, and for evaluation of vitamin D status in the setting
of renal failure (where 1-α-hydroxylase activity is decreased).1,7
While the gold standard for vitamin D measurement is liquid
chromatography coupled to tandem mass spectrometry (LC-MS/MS), most
laboratories utilize immunoassays (including radioimmunoassays,
chemoluminescent immunoassays, and enzyme-linked immunoassays) for vitamin D
quantitation.1,7 One significant difference between these two
methods is that while LC-MS/MS can differentiate vitamin D3 and
vitamin D2 metabolites, immunoassays cannot.6 In
addition, the antibodies used in many 25(OH)D immunoassays often have lower
cross-reactivities with 25(OH)D2 and therefore may underestimate
this form when giving the total 25(OH)D value.6 These antibodies
also have varying cross-reactivities with other vitamin D metabolites and so
may result in an overestimation of the total 25(OH)D due to positive
interference from these metabolites.6
Another advantage of the LC-MS/MS method is that it can
detect C3 epimers of 25(OH)D, while immunoassays cannot.8 The
physiologic significance of these epimers has not yet been clearly delineated,
but recent evidence has shown that while these epimers do not affect calcium concentrations,
they do contribute to suppression of PTH levels.8 In addition, while
these epimers comprise a low proportion (about 2-3%) of the overall 25(OH)D
concentration in adults, they have been found in significantly higher
proportions (up to 60%) in infant and pediatric populations.8,9
Thus, the detection of these epimers (and their quantitation, which is possible
through high-performance LC-MS/MS) may be more important in these patient
Vitamin D Results
The optimal serum levels of 25(OH)D are not universally
established. First of all, levels vary with factors affecting sunlight exposure
including latitude, skin pigmentation, and sunscreen use.1 Levels
also demonstrate significant seasonal variation, with winter measurements up to
40-50% lower than summer measurements.1 Recommended minimum 25(OH)D
levels for optimal bone health differ among various national organizations and
generally range from 20 ng/mL to 30 ng/mL; as mentioned above, these thresholds
are controversial and there is no established consensus.10-12
Vitamin D deficiency is very common, with the majority of
patients exhibiting no clinical symptoms and normal calcium and phosphate concentrations.
However, a significant proportion of these asymptomatic patients will have
increased PTH levels and concomitant increased risk of osteopenia/osteoporosis
and fractures; therefore, all patients with vitamin D deficiency should be
treated with repletion.13 If deficiency is severe and persistent,
bone demineralization with rickets (in children) and osteomalacia (in adults
and children) can develop. In contrast, vitamin D toxicity is very rare and is
usually associated with over-supplementation; patients develop hypercalcemia
with related symptoms including confusion, muscle weakness, nausea and
vomiting, and polydipsia and polyuria.14
Recent studies have linked vitamin D deficiency (usually
with residency at higher latitudes) to a wide variety of clinical disorders
ranging from autoimmune diseases (multiple sclerosis, rheumatoid arthritis,
type I diabetes), to cancers (including colon, breast, and prostate), to
psychiatric illnesses (schizophrenia, depression), and cardiovascular disease
(including hypertension and congestive heart failure).15 Whether
these links possess a causal basis or are merely associative needs to be
further investigated. Nevertheless, what is certain is that understanding the
functions of vitamin D in the body and methodologies of vitamin D measurement
in the laboratory is crucial in appreciating its clinical significance and
various, ever-expanding applications in disease pathophysiology and management.
McPherson RA, Pincus MR. Henry’s Clinical
Diagnosis and Management by Laboratory Methods. Elsevier Health Sciences; 2017.
Brown AJ. Regulation of vitamin D action.
Nephrology, dialysis, transplantation: official publication of the European
Dialysis and Transplant Association-European Renal Association. 1999 Jan 1;14(1):11-6.
Armas LA, Hollis BW, Heaney RP. Vitamin D2 is
much less effective than vitamin D3 in humans. The Journal of Clinical
Endocrinology & Metabolism. 2004 Nov 1;89(11):5387-91.
Cashman KD, Hayes A, Galvin K, Merkel J, Jones
G, Kaufmann M, Hoofnagle AN, Carter GD, Durazo-Arvizu RA, Sempos CT.
Significance of serum 24, 25-dihydroxyvitamin D in the assessment of vitamin D
status: a double-edged sword?. Clinical chemistry. 2015 Apr 1;61(4):636-45.
Clarke W. Contemporary practice in clinical
chemistry. Amer Assn for Clinical Chemistry; 2016.
Zerwekh JE. Blood biomarkers of vitamin D
status. The American journal of clinical nutrition. 2008 Apr 1;87(4):1087-91.
Hollis BW. Assessment and interpretation of
circulating 25-hydroxyvitamin D and 1, 25-dihydroxyvitamin D in the clinical
environment. Endocrinology and Metabolism Clinics. 2010 Jun 1;39(2):271-86.
Lutsey PL, Eckfeldt JH, Ogagarue ER, Folsom AR,
Michos ED, Gross M. The 25-hydroxyvitamin D3 C-3 epimer: distribution,
correlates, and reclassification of 25-hydroxyvitamin D status in the
population-based Atherosclerosis Risk in Communities Study (ARIC). Clinica
chimica acta. 2015 Mar 10;442:75-81.
Singh RJ, Taylor RL, Reddy GS, Grebe SK. C-3
epimers can account for a significant proportion of total circulating
25-hydroxyvitamin D in infants, complicating accurate measurement and
interpretation of vitamin D status. The Journal of Clinical Endocrinology &
Metabolism. 2006 Aug 1;91(8):3055-61.
Del Valle HB, Yaktine AL, Taylor CL, Ross AC,
editors. Dietary reference intakes for calcium and vitamin D. National
Academies Press; 2011 Apr 30.
Vieth R. What is the optimal vitamin D status
for health?. Progress in biophysics and molecular biology. 2006 Sep 1;92(1):26-32.
American Geriatrics Society Workgroup on Vitamin
D Supplementation for Older Adults. Recommendations abstracted from the
American geriatrics society consensus statement on vitamin D for prevention of
falls and their consequences. Journal of the American Geriatrics Society. 2014
Valcour A, Blocki F, Hawkins DM, Rao SD. Effects
of age and serum 25-OH-vitamin D on serum parathyroid hormone levels. The
Journal of Clinical Endocrinology & Metabolism. 2012 Nov 1;97(11):3989-95.
Ozkan B, Hatun S, Bereket A. Vitamin D
intoxication. Turk J Pediatr. 2012 Mar 1;54(2):93-8.
Holick MF. Vitamin D deficiency. New England
Journal of Medicine. 2007 Jul 19;357(3):266-81.
-Michelle Lin, MD, is a second-year anatomic and clinical pathology resident at Houston Methodist Hospital in Houston, Texas.
This last month, I rotated through our Children’s hospital,
which included reviewing hemoglobin electrophoresis tests. I’d learned about
them before in residency, but they can be quite more interesting (complicated)
than I expected.
Hemoglobin electrophoresis is a blood test to look at
different types of hemoglobin to determine if there are any abnormalities. In a
children’s hospital it is frequently ordered as a reflex for an abnormal
newborn screen or when a child is incidentally found to be anemic. The test is
performed in 2 stages. 1st lysed blood samples are run on gel
electrophoresis and different types of hemoglobin are separated as they move at
different speeds. Several types of hemoglobin will run within the same region,
so a secondary method of separation is always employed.
Below, you can see how some bands in the same area of an acidic gel (agarose) are actually very
different on the alkaline gel (cellulose
acetate) and vice versa.
At our hospital, we use HPLC
and measure retention times of the hemolysate to quantify and identify
different hemoglobin types present. As a basic primer you should recall that hemoglobin is a tetramer with a pair of alpha globin + a pair of either beta, delta or gamma globin
(each separate genes).
Alternative hemoglobins are enriched in populations where
malaria is endemic as these variants may provide improved fitness by promoting
resistance to the malarial parasite that reproduces inside red blood cells. Thus,
many people of African or south east Asian descent may carry these variants.
Our case is that of a 2 year old girl with anemia who had
testing sent by her primary care doctor for the following CBC:
This is indicative of microcytic anemia, but unlike some Thalessemias
the RBC isn’t very high. More on this later.
Looking at the gel result, there is a large band in the area
coinciding with Hgb C. We also see the normal Hgb A2 and a small amount of Hgb
F. We know Hgb F can be increased in Hgb SS and thus could also be present if
she had Hgb C trait or disease.
Looking at the next HPLC result, we see there is a similar very high level of Hgb C (68%) with corresponding levels of Hgb F and Hgb A2 (note: acetylated Hgb F and Hgb F are added together). Thus, this fits with a homozygous C with some compensatory A1 and F, right?
Remember Hgb C is a β -globin variant and
you only have 2 β -globin genes, so if you are homozygous
for the C variant on the β-globin gene (HBB), then Hgb A1, which is
made of normal β-globin would be impossible to produce.
Also you might be bothered by all of these small peaks. However, there are
often small peaks that can’t be definitively identified and are likely
post-translationally modified hemoglobin. But in the context of an abnormal Hgb
A1 that shouldn’t be there, we dug deeper.
One of the most common hemoglobinopathies is Beta Thalassemia (β-Thal), which clinically manifests when less of
the beta hemoglobin protein is produced. Heterozygous mutations lead to Beta Thalassemia
minor with minimal symptoms, while homozygous mutations lead to β-thal major with symptoms of anemia. Mutations in the β -globin gene, HBB,
can lead to complete loss of β-globin (β0 variant)
or partial of β-globin (β+ variant).
As this patient has less than 50% of Hgb A present (expected
amount), they could also have a β+ variant
as well. This would make them compound heterozygous for C and β+.
One of the hallmarks of Thalassemia is an increase in Hgb A2 (normal 2.5-3.5%).
Hemoglobin A2 is a normal variant of A that is composed of two alpha and two
delta chains (δ2α2). We see in our
case that the Hgb A2 is normal at 2.5%. So it seems the patient doesn’t display
a typical Thalassemia picture.
One condition that could create this scenario is if there is
a variant in the delta chain of A2
that causes it to elute differently. Indeed, there is a delta variant that
creates hemoglobin A2 prime (A2’)
that moves near the S region of the
HPLC. And when we look back at our unknown hemoglobins, Hgb X is marked at 1.03 of the S region and has an abundance of
3.9%. This supports it being the Hgb A2’ and if we add this together with the
Hgb A2 we get an elevated 6.6% A2 total,
which would be consistent with Beta Thalassemia.
Lastly, one would wonder if we could find this
third hemoglobin variant A2’ on the alkaline gel. Previous studies have shown
the A2’ variant is more negatively charged, so on a basic gel, it should move
further from the negative anode than the other hemoglobins. We don’t see
anything to the left of the HgbC, but if we flip the gel over and look under the patient label, you can see a
faint band that is likely the A2’!
In summary this case arose from 3 separate mutations in a
single patient. She was compound
heterozygous for a Hgb C and β+ variants in the β-globingene and she was heterozygous
for an A2’ variant on the delta-globin
gene. This was certainly a case
where paying close attention mattered.
Abdel-Gadir D, Phelan L, and Bain BJ.
Haemoglobin A2′ and its significance in beta thalassaemia diagnosis. Int J Lab
Hematol. 2009 Jun;31(3):315-9. doi: 10.1111/j.1751-553X.2008.01038.x. Epub 2008
-Dr. Charles Timmons MD PhD is a pediatric pathologist at Children’s Medical Center in Dallas, TX. His responsibilities include signing out hemoglobin electrophoresis, HPLC and globin sequencing, and has been residency director for 17 years.
-Jeff SoRelle, MD is a Chief Resident of Pathology at the
University of Texas Southwestern Medical Center in Dallas, TX. His
clinical research interests include understanding how the lab intersects
with transgender healthcare and improving genetic variant
When a patient gets their “testosterone test” at the doctor to assess their
libido, do they really know what they’re getting? Does your lab test for
testosterone, and are you confused about which of these confusingly-named tests
are in-house versus send-out? Do you need a refresher on the types of
testosterone tests out there and the clinical significance of each?
A Primer on Testosterone
Testosterone, being a fairly hydrophobic member of the steroid-ring family,
is the major androgen in males. Apart from its well-known function in promoting
the development of primary male reproductive organs and secondary male sex
characteristics, it also has important anabolic effects in maintaining muscle
mass, bone maturation, regulation of the hypothalamic-pituitary-adrenal axis
under stress, and even in promoting platelet aggregation through enhancing
platelet thromboxane A2 expression.1 In females, testosterone increases sexual arousal, and is in fact used
clinically as treatment for female sexual arousal disorders. So, clearly an
important member of the steroid family.
Being hydrophobic, much of the testosterone in the human body is not freely
available, but rather bound. Total testosterone signifies the total pool
of testosterone available in the human body, and is largely encompassed by the
majority of bound testosterone with a small (usually 1.5-2.0%)
proportion of free testosterone, which is biologically active. The bound
testosterone can further be subdivided into testosterone bound to sex-hormone
binding globulin (SHBG), a small glycoprotein that strongly binds various
androgens and estrogens, and testosterone bound toalbumin, which is a
relatively weak interaction.
Recently, the concept of bioavailabletestosterone has been
defined,2 based on the understanding that testosterone bound to SHBG (around 2/3rd
of the bound proportion) is relatively inaccessible, while testosterone bound
to albumin is weakly interacting, and thus potentially bioactive. Therefore,
the definition of bioavailable testosteroneincludes both free and
albumin-bound testosterone, which comprise the non-SHBG bound proportion.
How is testosterone measured?
Conventionally, total testosterone is measured through either immunoassays
(both radioimmunoassays, or more commonly, chemiluminescent immunoassays) or
mass spectrometry coupled with gas chromatography (GC/MS) or liquid
chromatography (LC-MS/MS). Isotope dilution mass spectrometry (IDMS) is the
reference method for testosterone measurement,3 but due to cost and convenience, most labs utilize immunoassays. Sex
hormone binding globulin (SHBG) is commonly measured through chemiluminescent
immunoassays, and also available for many platforms.4
There are two main approaches to the measurement of free testosterone,
which is significantly more challenging. The gold standard for free
testosterone measurement is equilibrium dialysis (see inset), a time consuming,
expensive, and laborious assay that uses semi-permeable membranes to measure
antibody-bound fractions of testosterone. Moreover, results can vary with pH,
temperature, and methods of dilution.5 Due to these complications, calculated free testosterone is an attractive
alternative used by many laboratories.
What is equilibrium
Equilibrium dialysis and ultrafiltration are reference methods used to
determine true free testosterone calculation. Briefly, a relatively large
quantity of serum (500 to 1000 uL) is placed in one chamber of an equilibrium
dialysis apparatus, which is comprised of two fluid chambers separated by a
semi-permeable membrane. Free-labeled testosterone passes through the
membrane, while testosterone bound to SHBG does not. The radioactivity in the
free chamber is quantified as a proportion of the total testosterone level,
as measured by another assay, such as LC/MS-MS.
What is calculated free testosterone, and how is it calculated?
Recognizing the difficulty of performing equilibrium dialysis on large volumes of testosterone specimens, several researchers have looked into devising good approximations of free testosterone through mathematical expressions modeling the distribution of testosterone among its various compartments. One of the most popular approximations, the Vermeulen equation developed by Dr. Alex Vermeulen,6 models the distribution of testosterone among the SHBG-bound, albumin-bound, and free component through association constants of testosterone among these compartments, and can be modeled by the equation in Figure 1, which depends on the total testosterone, SHBG concentration, and concentration of albumin (although this will be discussed below). The overall concordance of this method with apparent free testosterone obtained through equilibrium dialysis (AFTC), the reference method, is very good, with a correlation coefficient of 0.987 and mean values well within the SEM between the two methods.6
In studies of the variation of calculated free testosterone values to the
albumin concentration, Vermeulen et al. demonstrated that between “normal”
albumin concentrations ranging from 5.8–7.2 × 10−4 mol/L (40
to 50 g/L), the mean calculated free testosterone varied from 340 ± 40.9 pmol/L
assuming an albumin concentration of 40 g/L, to 303 ± 35.4 pmol/L assuming a
concentration of 50 g/L albumin. Moreover, the concordance of calculated FT
results to AFTC concentrations remained very good (correlation coefficient of
0.992) when an intermediate fixed albumin concentration (43 g/L) was used in
this calculation, compared to actual albumin levels. Overall, these
calculations suggest that for healthy individuals without marked abnormalities
in plasma protein composition, such as in nephrotic syndrome or cirrhosis of
the liver, or pregnant patients, a fixed albumin concentration could be used
without significantly affecting calculated FT results. Of course, in
individuals with marked changes in plasma proteins, the actual albumin
concentration should be accounted for.
Willem de Ronde et al5 compared five different algorithms for calculating free or
bioavailable, which includes the Vermeulen and Sodergard method (which use
similar parameters), as well as methods by Emadi-Konjin et al, Morris et
al, and Ly et al. In general, there was high concordance between the Vermeulen
and Sodergard methods (r=0.98) for measuring free testosterone, and lower, but
still reasonable (r=0.88) concordance between Vermeulen and other methods.
Fundamentally, the Vermeulen and Sodergard equations were derived from
experimentally derived association constants from the law of mass action, as
opposed to the other algorithms, which rely on experimentally derived free and
bioavailable testosterone measurements that was modeled by regression
equations, and thus depends on the accuracy of these measurements. Though the
experimental basis underlying the Vermeulen and Sodergard equations is
stronger, it is known that supraphysiologic concentrations of other steroid
hormones (estradiol or dihydrotestosterone), in competition for binding
sites to SHBG, can significantly underestimate free testosterone by any
of these methods. Of course, inaccuracies in the measurement of total
testosterone or SHBG can significantly affect results, as well as significant
perturbations in total serum protein concentrations (as mentioned above).
Since the publication of the above work, additional
calculations for free testosterone accounting for other modes of interaction of
SHBG such as allostery and dimerization have been published that may further
improve concordance with AFTC;7,8 however, further study is
needed to determine if these methods actually result in superior calculated FT
measurement for clinical decision making, as well as changes in sensitivity to
Why do accurate free testosterone measurements matter?
Testosterone bound to serum albumin is essentially inactive; therefore, the
only testosterone that is biologically relevant is free (and to a lesser
extent, bound to SHBG). Current consensus guidelines still support the use of
total testosterone for defining hypogonadism in men,9,10 although emerging studies and newer task-force consensus groups11,12 highlight an emerging role for both calculated and free testosterone
measurements in addition to total testosterone. The role of direct free
testosterone measurement is still hotly debated; a recent analysis of CAP
proficiency data indicates considerable heterogeneity among laboratories using
the reference methods described above, and suggests considerable cost savings
without significant loss of reliability can be achieved by using calculated or
FT bioavailable T over direct FT measurement.13 Further standardization of these assays is needed to better understand the
Ajayi A a. L, Halushka PV. Castration reduces platelet thromboxane A2
receptor density and aggregability. QJM. 2005;98(5):349-356.
Shea JL, Wong P-Y,
Chen Y. Free testosterone: clinical utility and important analytical aspects of
measurement. Adv Clin Chem. 2014;63:59-84.
Shacklady C, Cooper HC, et al. Isotope-Dilution Liquid Chromatography–Tandem
Mass Spectrometry Candidate Reference Method for Total Testosterone in Human
Serum. Clinical Chemistry. 2013;59(2):372-380.
Dittadi R, Fabricio
ASC, Michilin S, Gion M. Evaluation of a sex hormone-binding globulin automated
chemiluminescent assay. Scand J Clin Lab Invest. 2013;73(6):480-484.
Ronde W de, Schouw
YT van der, Pols HAP, et al. Calculation of Bioavailable and Free Testosterone
in Men: A Comparison of 5 Published Algorithms. Clinical Chemistry.
Verdonck L, Kaufman JM. A Critical Evaluation of Simple Methods for the
Estimation of Free Testosterone in Serum. None. 1999;84(10):3666-3672.
Zeinyeh W, Déchaud H, et al. Inverse relationship between hSHBG affinity for
testosterone and hSHBG concentration revealed by surface plasmon resonance. Molecular
and Cellular Endocrinology. 2015;399:201-207. doi:10.1016/j.mce.2014.10.002
Zakharov MN, Bhasin
S, Travison TG, et al. A multi-step, dynamic allosteric model of testosterone’s
binding to sex hormone binding globulin. Mol Cell Endocrinol.
Margo KL, Winn R.
Testosterone Treatments: Why, When, and How? AFP. 2006;73(9):1591-1598.
Association of Clinical Endocrinologists Medical Guidelines for Clinical
Practice for the Evaluation and Treatment of Hypogonadism in Adult Male Patients—2002
Update. Endocrine Practice. 2002;8(6):439-456. doi:10.4158/EP.8.6.439
Cunningham GR, Hayes FJ, et al. Testosterone therapy in men with androgen
deficiency syndromes: an Endocrine Society clinical practice guideline. J
Clin Endocrinol Metab. 2010;95(6):2536-2559. doi:10.1210/jc.2009-2354
Liu Z, Liu J, Shi
X, et al. Comparing calculated free testosterone with total testosterone for
screening and diagnosing late-onset hypogonadism in aged males: A
cross-sectional study. J Clin Lab Anal. 2017;31(5).
Morales A, Collier
CP, Clark AF. A critical appraisal of accuracy and cost of laboratory
methodologies for the diagnosis of hypogonadism: the role of free testosterone assays. Can
J Urol. 2012;19(3):6314-6318.
-Dr. Jim Hsu is a 2nd year pathology resident currently in training at Houston Methodist Hospital. After completing a M.D./Ph.D at the University of Texas Medical Branch in Galveston, he realized his passions remained in the lab, but wanted to bring that passion into patient care, and soon realized that pathology was the key to achieving both. His love for all things data drew him to pathology informatics, and with the suggestion of his mentor Dr. Wesley Long, to API. In particular, he is interested in the transformative power of data analysis in improving best practices, reducing error, and combating bias. Outside of the lab, he is interested in financial markets, algorithms, neuroscience, reading, and traveling (for the food, of course).
A 44 year old male with history of cocaine use presented with 1 year history of headache and progressive frontal lobe syndrome, including symptoms like apathy, personality changes, lack of ability to plan, poor working memory for verbal information or spatial information, Broca aphasia, disinhibition, emotional lability, etc. CT scan found extensive destruction of osteocartilaginous structures of the nasal cavity and MRI showed extensive edema of the frontal lobe. Biopsy showed chronic inflammation but negative for granulomatous inflammation. Patient’s CSF laboratory analysis was normal but ANCA was tested positive, in a P-ANCA pattern without MPO detectable. Patient was diagnosed as CIMDL. After stopping cocaine use, patient was doing better but still has mild frontal lobe syndrome.
Anti-neutrophil cytoplasmic antibody (ANCA) are a group of
autoantibodies that directed toward antigens expressed mainly in neutrophil
granulocytes, such as proteinase 3 (RP3) and myeloperoxidase (MPO). The
presence of ANCA is mainly associated with a distinct form of small vessel
vasculitis, known as ANCA-associated vasculitis, but is also detected in other
disease, like autoimmune hepatitis, primary sclerosing cholangitis, ulcerative
colitis, and other chronic inflammatory disease. The gold standard laboratory
method to screen ANCA is indirect immunofluorescence assay (IFA or IIF), which qualitatively
capture antibodies in serum/or plasma bound to fixed human neutrophil
Two form of ANCA-associated vasculitis, granulomatous with
polyangiitis (GPA) and eosinophilic granulomatous with polyangiitis (EGPA), are
systemic diseases that commonly associated with necrotizing granulomatous
vasculitis. GPA has a primary involvement of the upper and lower respiratory
tract and kidney. Autoantibodies to PR3 are found in 90% of active GPA cases,
which generates a cytoplasmic-ANCA (C-ANCA) pattern on ANCA IFA test. EGPA is a
rare form of systemic necrotizing vasculitis characterized by asthma and
eosinophilia. A perinuclear-ANCA (P-ANCA) IFA pattern directing towards MPO
antibody are often seen in EGPA cases.
Both GPA and EGPA may also present with sinonasal
involvement, causing non-infectious inflammatory lesions of the sinonasal
tract. Sinonasal inflammatory disease can also result from bacterial and fungal
infections, or other non-infectious process, such as sarcoidosis,
polychondritis, or obstruction. ANCA is detected in the majority of GPA and
EGPA case, therefore it provides useful information in differential diagnosis
of sinonasal inflammatory disease. Both GPA and EGPA are autoimmune diseases,
corticosteroids and immunosuppressive agents are effective treatment.
Sinonasal inflammation can also been seen in a subset of
patients with cocaine abuse, who normally present with midline destructive
lesions, known as cocaine-induced midline destruction lesions (CIMDL). Long-term
cocaine use has been associated with ischemia of mucosal tissue, cartilage and
bone, and cocaine abuser using intranasal inhalation route can have midline
deformity and septal perforation. Interestingly, ANCA are also found in a large
portion of CIMDL, and in contrast to GPA or EGPA, ANCA in CIMDL are primarily
directed against neutrophil elastase, generate a P-ANCA or atypical P-ANCA
pattern, without detection of MPO. Therefore, ANCA serology testing could help
the differentiation between CIMDL and GPA although these two can overlap
clinically and histopathologically. Also, CIMDL does not respond well to
immunosuppressive therapy and only consistent removal of stimuli (cocaine) can
halt the disease process.
Montone KT. Differential Diagnosis of Necrotizing Sinonasal Lesions. Arch Pathol Lab Med. 2015 Dec;139(12):1508-14. doi: 10.5858/arpa.2015-0165-RA.
Trimarchi M, Bussi M, Sinico RA, Meroni P, Specks U. Cocaine-induced midline destructive lesions – an autoimmune disease? Autoimmun Rev. 2013 Feb;12(4):496-500. doi: 10.1016/j.autrev.2012.08.009. Epub 2012 Aug 24.
Madani G, Beale TJ. Sinonasal inflammatory disease. Semin Ultrasound CT MR. 2009 Feb;30(1):17-24.
Timothy R. Helliwell Non-infectious Inflammatory Lesions of the Sinonasal Tract. Head Neck Pathol. 2016 Mar; 10(1): 32–39.
-Xin Yi, PhD, DABCC, FACB, is a board-certified clinical chemist,
currently serving as the Co-director of Clinical Chemistry at Houston
Methodist Hospital in Houston, TX and an Assistant Professor of Clinical
Pathology and Laboratory Medicine at Weill Cornell Medical College.
Given my previous work in lab value changes in transgender
individuals on hormone therapy, I was recommended to consider discussing the
case of Olympic mid-distance runner, Caster Semenya. Although she is not
transgender, this professional runner from South Africa has won her last 30
races and been scrutinized for her muscular build as having potentially higher
levels of testosterone, a condition called hyperandrogenism. The International
Olympic Committee’s (IOC) regulations require testosterone levels to be below a
certain threshold for female athletes.
While no competitor can achieve great victories without hard
work and practice, there are certainly examples of outliers whose genetics give
them an advantage. However, I don’t think we would endorse shortening Michael
Phelps’ arms or lobotomizing chess master Bobby Fisher to decrease their inborn
advantages for a level playing field.
But this gets into an area of ethics that I’m not an expert
on, so instead I will stick to my area of science and examine what evidence may
exist to support the IOC’s policy. Then I will extrapolate the results from our
study of transgender individuals to see if hormone regulation may impact
contributions to athleticism. The most strongly shifted lab values in hormone
therapy for transgender individuals are red blood cells (including oxygen-carrying
hemoglobin) and creatinine (byproduct of muscle used to monitor kidney
function, but also reflects total muscle mass).
Once looking more closely at this topic, I realized there is
a lot to say about the contributions of 1) muscle mass and 2) red blood cells
to athleticism. So, I will discuss muscle mass this month and wait until next
month to discuss hemoglobin levels (including athletic performance by blood
Mid-distance running, which is Caster Semenya’s sport, is a
mix of anaerobic and aerobic activity. This means having more muscle would be
advantageous. This is supported by a study that was commissioned by the IAAF
(International Association of Athletics Federation), which shows a 1.8-2.6%
increased competitive advantage in short distance track events (400m, 800m and,
400m hurdles)1. However, this study had several limitations. First,
the sample size was quite low with only 22 female athletes. Next, they use a
p-value of 0.05 for significance without correction for multiple hypothesis
testing (21 hypotheses tested representing each event), which increases the
likelihood of a false positive result by chance.
What makes me curious is whether following the International
Olympic Committee’s recommendations of lowering testosterone levels would even
have a meaningful impact and improve competitiveness?
From my research, I know that adding testosterone to
individuals assigned female at birth to transition to transgender males (TM ) does
substantially increase creatinine (p<0.005, Figure 1)2 to male
levels (baseline TW). This is likely not due to changes in kidney function
(although this has not yet been proven), but rather due to increased muscle
However, the inverse is not quite true for transgender women
who take combinations of estrogen for feminization and spironolactone to block
the effects of testosterone. In these patients, we see a slight decrease in the
creatinine (TW). While this decrease is statistically significant, the range is
not clinically different from male creatinine levels. This concurs with the
observations that musculature in transgender women does not change
substantially upon taking hormone altering medication.
A more rigorous examination of muscle mass, performed by MRI
measurement, determined that after 1 year of hormone therapy testosterone
increased muscle mass in transgender men to biological male levels3,
similar to our observations of creatinine. Further, they saw a significant
reduction in muscle mass from baseline of transgender women on hormone therapy
for 12 months, but it was still much higher than the muscle mass of biologic
Therefore, were Casten Semenya to take testosterone blocking
medication, I suspect there would be little impact on her overall muscle mass.
Which is one of, if not the explicit purpose of taking testosterone lowering
medicine. The strength of my conclusions is limited by the fact that we don’t
know Casten Semenya’s testosterone levels, and furthermore a hyperadrogenic
female is not the same as a male-to-female transgender woman.
As mentioned above, I will continue this discussion next
month with an exploration of how testosterone lowering therapy could affect red
blood cell levels, which would affect athletic performance differently.
Bermon S and Garnier P. Serum androgen levels
and their relation to performance in track and field: mass spectrometry results
from 2127 observations in male and female elite athletes. British Journal of
Sports Medicine. 2017; 51(17): 1309-1314.
SoRelle JA, Jiao R, Gao E et al. Impact of
Hormone Therapy on Laboratory Values in Transgender Patients. Clin Chem. 2019; 65(1): 170-179.
Jones BA, Arcelus J, Bouman WP, Haycraft E. Sport
and Transgender People: A Systematic Review of the Literature Relating to Sport
Participation and Competitive Sport Policies. Sports Med. 2017;47(4):701-716.
-Jeff SoRelle, MD is a Molecular Genetic Pathology fellow at the University of Texas Southwestern Medical Center in Dallas, TX. His clinical research interests include understanding how the lab intersects with transgender healthcare and advancing quality in molecular diagnostics.
Insulin antibodies are seen in two conditions: 1, in insulin-naïve type-1
diabetic patients, insulin antibodies are developed together with some other
autoantibodies against pancreatic islet cells; 2, in patients being treated
with insulin, antibodies can be developed against exogenous insulins, in both
type-1 and type-2 diabetes. These antibodies against exogenous insulins are
found in >95% of patients treated with porcine and bovine insulins (1).
Although the prevalence has decreased after the introduction of human insulin
and insulin analogues, it is still not uncommon to detect these antibodies in
insulin treated patients (2). However, these antibodies are rarely of clinical
significance and laboratory test for insulin antibodies in insulin-treated
patients has limited clinical value, except in rare cases where these
antibodies are found to have immunologic role, causing insulin resistance. In
some of these cases, postprandial hyperglycemia and nighttime hypoglycemia are
both described due to reversible binding of insulin from antibodies (3), and
patients were reported to respond to immunosuppressive therapies, and plasmapheresis
in severe cases.
worked up a case for possible immunologic insulin resistance caused by insulin
antibodies. In this case, patient is a 45 years old female with uncontrolled
type-1 diabetes. She was found to have all four antibodies positive, including
zinc transporter 8, islet
antigens glutamate decarboxylase 65 (GADA), IA-2A, and insulin antibodies. Patient
has been on multiple dose insulin injection (MDI) therapy, including insulin
determir, aspart and lispro. She was reported to be compliant with medications
and low carb diet. However, patient has poor glycemic control and presents with
recurrent diabetic ketoacidosis. She was given high doses of insulins, but
still presented with recurrent DKA and occasional hypoglycemia. Her HbA1c was
consistently at >10% with daily glucose measured up to 500 mg/dL.
insulin antibody and insulin receptor antibody were considered after ruling out
more common causes of her uncontrolled diabetes. These two tests were then performed
at a reference laboratory and patient was found to have positive insulin
antibodies to analog insulin (determir and lispro) and negative insulin
receptor antibodies. Significant insulin resistance by insulin antibodies was
not found and the antibodies level did not suggest immunosuppressive therapy. Still,
given her poor controlled diabetes, patient’s insulin was switched to human
insulin and she was also recommend for pancreas transplant.
Greenfield JR, Tuthill A, Soos
MA, Semple RK, Halsall DJ, Chaudhry A, O’Rahilly S. Severe insulin
resistance due to anti-insulin antibodies: response to plasma exchange and
immunosuppressive therapy. Diabet Med. 2009 Jan;26(1):79-82. doi:
Hall TR, Thomas JW, Padoa CJ, Torn
C, Landin-Olsson M, Ortqvist E, Hampe CS. Longitudinal epitope analysis of
insulin-binding antibodies in type 1 diabetes. Clin Exp Immunol. 2006
Hao JB, Imam S, Dar
P, Alfonso-Jaume M, Elnagar N, Jaume JC. Extreme Insulin
Resistance From Insulin Antibodies (Not Insulin Receptor Antibodies)
Successfully Treated With Combination Immunosuppressive Therapy. Diabetes
Care. 2017 Feb;40(2):e19-e20. doi: 10.2337/dc16-1975. Epub 2016
-Xin Yi, PhD, DABCC, FACB, is a board-certified clinical chemist, currently serving as the Co-director of Clinical Chemistry at Houston Methodist Hospital in Houston, TX and an Assistant Professor of Clinical Pathology and Laboratory Medicine at Weill Cornell Medical College.