Pathologist On Call: Fluctuating Parathyroid Hormone with Normal Calcium in an Elderly Man

Case:

A 75 year old Alzheimer’s dementia patient.  Parathyroid hormone (PTH) levels were ordered.

Analyte

(Reference

Range)

05/13 10/13 12/13 7/14 10/14 04/15 09/15 03/16 07/16
PTH

(10-65 pg/mL)

869 42 864 47 1180 48
Ca2+

(8.8-10.2 mg/mL)

10.3 10.5 10 10 9.6 10
Vit D

(2-100 ng/mL)

26 21 39 49 39 57 19

 

Why order PTH? 

PTH is ordered to assess for hyperparathyroidism.  There are two forms of hyperparathyroidism: primary and secondary.  Primary hyperparathyroidism can be caused by a parathyroid (PT) adenoma,  PT hyperplasia, or a non-PT malignancy such as squamous cell cancer or multiple myeloma.  Secondary hyperparathyroidism occurs in response to hypocalcemia which can arise from insufficient intake of vitamin D or chronic renal failure (which results in insufficient vitamin D).   There is weak evidence suggesting a positive correlation between PTH and cognitive decline.(1, 2)  Progression of cognitive decline is slowed when PTH and vit D levels are normalized.

Action of PTH: PTH is a peptide hormone that controls calcium levels in the blood. It is secreted as a prohormone and is cleaved in the blood.  The 34 residue N-terminal fragment is active and has a half-life of about 5 minutes.  The C-terminal end has a half-life or 2 hours and is diagnostically insignificant because it is physiologically inactive.  PTH activates receptors on osteoclasts which causes them to release bone calcium.  PTH also increases renal synthesis of 1,25 OH2 vitamin D which, in turn, increases intestinal absorption of calcium.

What would make the PTH level fluctuate so much?

This is most likely a case of incipient normocalcemic primary hyperparathyroidism (NPH).(3-5)  PTH levels are higher than normal but calcium levels are normal.  PTH levels tend to fluctuate. Calcium can also be sometimes elevated as well.   The disease is thought to be a mild or early form of hyperparathyroidism and 20 percent of patients go on to develop worsening hyperparathyroidism. How should NPH be managed?  Parathyroidectomy or monitoring are the primary alternatives; however, the best way to manage this disease is unknown.

 

References

  1. Lourida I, Thompson-Coon J, Dickens CM, et al. Parathyroid hormone, cognitive function and dementia: A systematic review. PLoS ONE 2015;10.
  1. Björkman MP, Sorva AJ, Tilvis RS. Does elevated parathyroid hormone concentration predict cognitive decline in older people? Aging Clinical and Experimental Research 2010;22:164-9.
  1. Shlapack MA, Rizvi AA. Normocalcemic primary hyperparathyroidism-characteristics and clinical significance of an emerging entity. Am J Med Sci 2012;343:163-6.
  1. Lowe H, McMahon DJ, Rubin MR, Bilezikian JP, Silverberg SJ. Normocalcemic primary hyperparathyroidism: Further characterization of a new clinical phenotype. Journal of Clinical Endocrinology and Metabolism 2007;92:3001-5.
  1. Crowley RK, Gittoes NJ. Elevated PTH with normal serum calcium level: A structured approach. Clinical Endocrinology 2016;84:809-13.

 

Schmidt-small

-Robert Schmidt, MD, PhD, MBA, MS is currently an Associate Professor at the University of Utah where he is Medical Director of the clinical laboratory at the Huntsman Cancer Institute and Director of the Center for Effective Medical Testing at ARUP Laboratories.

 

 

Chemistry Case Study: Unexplained Metabolic Acidosis

Case Workup

A 24-year-old female at 34 weeks of gestation was transferred from an outside hospital with history of nephrolithiasis and right side pyelonephritis, for which she underwent stent placement 2 weeks ago. She started experiencing severe pain and muscle spasms in her hip and was unable to move her leg due to the pain. She had decreased appetite and also noted vomiting. Her bilirubin and aminotransferases were found to be elevated. Additionally, her blood gas analysis showed a bicarbonate of 9 mEq/L, pH of 7.2 with 99% SpO2. Our clinical chemistry team was consulted on her low pH.

Patient’s laboratory workup is shown in the table below. We first ruled out some common causes of metabolic acidosis, including lactic acidosis and diabetic ketoacidosis. Ingestion of toxic alcohols was ruled out based on normal osmolality and osmolar gap. Normal BUN, creatinine, and their ratio ruled out renal failure.

Positive urinary ketones were noted, with an elevated anion gap. Serum beta-hydroxybutyrate was therefore measured and a result of 3.0 mmol/L (ref: <0.4 mmol/L) confirmed ketoacidosis. Patient had no history of diabetes and no recent alcohol consumption. On the basis of excluding other causes, and also considering her decreased appetite and recurrent vomiting, it is believed that ketoacidosis was caused by “starvation.”

Test Result Ref * Test Result Ref *
Albumin 2.0 3.5 – 5.0 g/dL pH 7.24 7.32-7.42
ALK 139 35 – 104 U/L pCO2 (V) 21 45-51 mmHg
ALT 177 5 – 50 U/L pO2 (V) 46 25-40 mmHg
AST 159 10 – 35 U/L O2 Sat (V) 72 40 – 70 %
Total Bili 2.0 0.0 – 1.2 mg/dL Glucose 74 65-99 mg/dL
Direct Bili 1.5 0.0 – 0.3 mg/dL Urine ketones 2+ Negative
Lactic acid 0.9 0.5 – 2.2 mmol/L Urine protein 2+ Negative
Protein 6.0 6.3 – 8.3 g/dL Chloride 104 98-112 mEq/L
Sodium 138 135-148 mEq/L CO2 9 24-31 mEq/L
Potassium 4.6 3.5-5.0 mEq/L Anion gap 25 7-15 mEq/L
Creatinine 0.6 0.5 – 0.9 mg/dL eGFR >90  >90 mL/min/1.73 m2
BUN 8 6 – 20 mg/dL Osmolality 286 275 – 295 mOsm/kg

* Reference ranges are for normal adults, not for pregnant women.

Discussion

With optimal glucose level and sufficient insulin secretion, glucose is converted by glycolysis to pyruvate, which is then converted into acetyl-CoA and subsequently into the citric acid cycle to release chemical energy in the form of ATP. When glucose availability becomes limited, fatty acid is used as an alternative fuel source to generate acetyl-CoA. Ketone bodies are generated in this process, and their accumulation result in metabolic acidosis. In healthy individual, fasting is seldom suspected to be the cause of metabolic acidosis. Sufficient insulin secretion prevents significant free fatty acid accumulation. However, under certain conditions when there is a relatively large glucose requirement or with physiologic stress, 12 to 14 hour fast could lead to significant ketone bodies formation, resulting in overt ketoacidosis (1-3).

Ketoacidosis is most commonly seen in patients with diabetic ketoacidosis. Similar metabolic changes are seen with poor dietary intake or prolonged fasting and resulting acidosis is referred to as “starvation ketoacidosis” (2). During pregnancy, especially in late pregnancy, there is an increased risk for starvation ketoacidosis, due to reduced peripheral insulin sensitivity, enhanced lipolysis, and increased ketogenesis. In this setting, short period of starvation can precipitate ketoacidosis (1-2, 4). Other cases described with starvation ketoacidosis include patients on strict low-carbohydrate diet (5-6), young infants after fasting (7), and patients with prolonged fasting before surgery (3).

Although starvation ketoacidosis is rare, healthcare provider should be aware of this entity especially in pregnant patients, because late recognition and delay in treatment are associated with a greater risk for impaired neurodevelopment and fetal loss (2). Moreover, given the popularity of low-carbohydrate diet nowadays, starvation ketoacidosis should be considered when assessing patient’s acid-base imbalance in conjunction with their dietary lifestyles.

References

  1. Frise CJ,Mackillop L, Joash K, Williamson C. Starvation ketoacidosis in pregnancy. Eur J Obstet Gynecol Reprod Biol. 2013 Mar;167(1):1-7.
  2. Sinha N,Venkatram S, Diaz-Fuentes G. Starvation ketoacidosis: a cause of severe anion gap metabolic acidosis in pregnancy. Case Rep Crit Care. 2014;2014:906283.
  3. Mostert M, Bonavia A. Starvation Ketoacidosis as a Cause of Unexplained Metabolic Acidosis in the Perioperative Period. Am J Case Rep. 2016; 17: 755–758.
  4. Mahoney CA. Extreme gestational starvation ketoacidosis: case report and review of pathophysiology. Am J Kidney Dis. 1992 Sep;20(3):276-80.
  5. Shah P,Isley WL. Ketoacidosis during a low-carbohydrate diet. N Engl J Med. 2006 Jan 5;354(1):97-8.
  6. Chalasani S, Fischer J. South Beach Diet associated ketoacidosis: a case report. J Med Case Rep. 2008;2:45. Epub 2008 Feb 11.
  7. Toth HL, Greenbaum LA. Severe acidosis caused by starvation and stress. Am J Kidney Dis. 2003;42(5):E16.

 

Xin-small

-Xin Yi, PhD, DABCC, FACB is a board-certified clinical chemist. She currently serves 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.

Vitamin Deficiency or Acute Leukemia?

67 year old patient with a history of uterine carcinoma (leiomyosarcoma), presented with pancytopenia and history of B-12 deficiency. CBC showed

  • WBC 4.1 K/ul
  • RBC *2.37 M/ul
  • Hgb *7.2 g/dl
  • MCV 91.1 fl
  • MCH 30.4 pg
  • MCHC 33.3 %
  • Platelets *25 K/ul

Peripheral blood differential count showed 3.5 % bands, 68.5 % Neutrophils, 3.5 % Eosinophils, 11.5 % Lymphocytes and 13.0 % Monocytes

Bone marrow differential count of the bone marrow showed 65.0 % Erythroid Precursors with 48.4% erythroblasts and 7% myeloblasts

Several erythroblasts were seen, which often had overlapping morphological features with myeloblasts. Erythroblasts had slightly coarser nuclear chromatin compared to myeloblasts and often had deeply basophilic vacuolated cytoplasm. Erythroid maturation was markedly megaloblastic /dysplastic and left shifted with marked preponderance of erythroblasts. Dysplastic forms characterized by presence of precursors with irregular nuclear borders along with few multinucleated forms and gigantoblasts were present.

Cells counted as myeloblasts had high N/C ratio, finer nuclear chromatin with occasionally distinct 1 to 2 nucleoli and scant cytoplasm.

Bone marrow with erythroid hyperplasia
Bone marrow with erythroid hyperplasia
Megaloblastic erthroid precursors with binucleate forms
Megaloblastic erthroid precursors with binucleate forms

Discussion:

The current WHO classification subtypes acute erythroid leukemia into two categories based on the presence or absence of significant myeloid component.

Erythroleukemia or Erythroid/Myeloid (FAB subtype A – M6a) comprises of more than 50% erythroid precursors among all nucleated cell population of bone marrow and more than 20% myeloblasts among non erythroid cells.

Pure erythroid leukemia (FAB subtype B – M6b) comprises of more than 80% immature cells of erythroid lineage with no evidence of a significant myeloid component

The most common reactive process that can mimic acute erythroid leukemia is megaloblastic anemia caused by vitamin B12 and folate deficiency. Features associated with pernicious anemia are hemolysis with increased mean corpuscular volume (MCV), hypersegmented neutrophils, leukopenia and thrombocytopenia increased LDH and urobilinogen. Bone marrow findings show hypercellular marrow witn marked erythroid hyperplasia. Other non-neoplastic diseases mimicking acute erythroid leukemia are post-chemotherapy recovery, parvovirus infection, drug effect, heavy metal intoxication and congenital dyserythropoiesis. A detailed clinical history, laboratory work up, peripheral blood and bone marrow examination, cytochemical, immunoshistochemical, flow cytometry, cytogenetic and molecular studies are required for the diagnosis of acute erythroid leukemia.

The oncologist was contacted and it was confirmed that B12 was repleted before the bone marrow study was performed. Diagnosis of acute erythroid /myeloid leukemia was only made after it was confirmed with the oncologist that patient was not B12 deficient at the time of the study.

Vajpayee,Neerja2014_small

-Neerja Vajpayee, MD, is an Associate Professor of Pathology at the SUNY Upstate Medical University, Syracuse, NY. She enjoys teaching hematology to residents, fellows and laboratory technologists.

Sample Stability and PO2–A Learning Opportunity

One of the interesting things about working in the field of laboratory medicine is that there are always opportunities for learning new things. Almost every call I get from my colleagues outside the lab allows me and the lab team these opportunities. And sometimes we are reminded of the reason we do the things we do, basically re-learning them.

Case in point: An ICU physician contacted the lab, understandably concerned. He had been monitoring the pO2 in a patient using an I-Stat point of care analyzer. Values had been in the range of 50-70 mmHg, and he had been adjusting ventilation on the basis of those results. A blood gas sample was sent to the main lab, analyzed on an ABL analyzer and gave a result of 165 mmHg, repeated shortly thereafter on a new sample with a 169 mmHg. Understandably, the physician wanted to know which analyzer was wrong and how he should be adjusting his patient’s ventilation.

We quickly did an investigation and determined an interesting fact that we hadn’t paid much attention to previously. A blood gas sample that is sent through the tube system that has any amount of air in the sample, will give falsely elevated pO2 result. We investigated this by collecting blood gas samples, running them on both the I-Stat and the ABL, and then sending them through the tube system and rerunning them on both instruments after tubing. The pO2 values matched on both instruments, both before and after tubing. But interestingly, if there was any air in the collection device when the device was sent through the tube system, the pO2 after tubing still matched on the two instruments, but the values were more than double the original values. If no air was present, there was very little change before and after tubing. We tested this by expressing all air from one set of samples before tubing and leaving air in the syringe on the other set.

The collection process for blood gas samples in our institution has always specified that the collector should express any air in the sample before sending the sample to the lab through the tube system, and after this incident the reason for that step became clear. However, the staff collecting blood gases on the floors needs to be periodically retrained in the collection, and the lab staff needs to be reminded that air in a blood gas syringe arriving through the tube station is a reason to reject the sample. We were reminded that education needs to be a continuous process. We also learned that when we discover the reason for a process, it’s a good idea to document that reason in order to both understand the need and to help motivate people to follow it.

-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.

Ammonia and Hyperammonemia

Ammonia is a small molecule that is produced as a part of normal tissue metabolism. Its formation results from the breakdown of compounds containing nitrogen, such as the amino groups in proteins and the nitrogenous bases in nucleic acids. In the tissues, ammonia is stored mainly in the form of amino acids, specifically the amino acid glutamine which has three amino groups. Normally, the body can remove excess ammonia easily via the liver pathway known as the urea cycle. This short, 4-step cyclical pathway converts two ammonia molecules into a small, water soluble urea molecule, making it able to be easily excreted in the urine. Without a functional urea cycle however, the body has no other adequate mechanism for getting rid of the ammonia that is constantly being produced by metabolism.

Liver damage or disease can disrupt the urea cycle, causing blood ammonia levels to rise. This is the most common cause of elevated ammonia in the adult population. In a pediatric patient, elevated ammonia is frequently seen as a consequence of an inborn error of metabolism (IEM). Many IEM, especially those in the urea cycle pathway, will result in elevated blood ammonia levels. In addition, in IEM causes, the ammonia concentrations may be well over 1000 µmol/L, when the normal range of ammonia is generally in the 30 – 50 µmol/L range. Elevated blood ammonia concentrations are serious because ammonia is toxic to the brain. The higher the ammonia concentration is, and the longer it stays high, the more brain damage that will occur.

Interestingly, the concentration of ammonia in the blood may not correlate with the neurological symptoms that are seen. Usually if the ammonia concentration is <100 µmol/L, the person will show no symptoms at all. Concentrations of ammonia in the 100 – 500 µmol/L range are associated with a wide variety of symptoms including: loss of appetite, vomiting, ataxia, irritability, lethargy, combativeness, sleep disorders, delusions and hallucinations. These patients may present with an initial diagnosis of altered mental status, and if there is no reason to suspect an elevated ammonia, the symptoms may lead to drug or alcohol testing. When ammonia concentrations are >500 µmol/L, cerebral edema and coma may be seen, with cytotoxic changes in the brain. Ammonia concentrations in the 1000+ µmol/L range are extremely critical and are treated aggressively with dialysis to pull the ammonia out of the system. In particular, urea cycle defects require close monitoring of ammonia and glutamine concentrations, with immediate response when they rise.

Laboratory testing for ammonia is often problematic as contamination can occur from a number of sources including atmospheric ammonia, smoking and poor venipuncture technique. In addition if the sample is not centrifuged and analyzed promptly, ammonia is formed by the continuous deamination of amino acids and the concentration increases by 20% in the first hour and up to 100% by 2 hours. Consequently samples to be tested for ammonia should be placed on ice immediately after being collected and transported to the lab for analysis as soon as possible. Many minimally elevated ammonia results are a consequence of poor sample handling. However, a truly elevated ammonia is a critical lab finding that should be addressed immediately.

-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.

Ketones

Most people who work in a clinical laboratory know a little about ketones or ketone bodies. The two facts that most people know include: 1) when you perform a urinalysis (UA), it includes a semiquantitative ketone result, and 2) high ketones are seen in diabetic ketoacidosis. But what is a ketone, where do they come from, and what are we measuring when we measure ketones?

In the laboratory medicine world, “ketones” refers specifically to acetoacetate (Acac), acetone and beta-hydroxybutyrate (BOHB). When the human body cannot utilize glucose, either because it is not present (fasting, starvation) or because it is present but cannot be used (lack of insulin to get glucose into the cells), the body instead breaks down fatty acids for energy. Fatty acids are mostly made up of long chains of carbons with hydrogens attached, so one of the main products of fat breakdown is 2-carbon acetyl-CoA. When a person is using lots of fats, like when they cannot use glucose, the production of acetyl-CoA exceeds the body’s ability to metabolize it via the Kreb’s cycle and it ties up lots of coenzyme A (CoA) needed for other processes. Thus, the body combines two excess acetyl-CoA into an acetoacetate, freeing up the CoA. The more acetyl-CoA produced from fat breakdown, the more acetoacetate produced. From there, the acetoacetate is converted to BOHB enzymatically or degrades spontaneously to acetone. BOHB is a dead end. Once there, the BOHB simply continues to build up until the production of acetyl-CoA no longer exceeds its utilization capacity. At that point, the BOHB is converted back to acetoacetate and then to acetyl-CoA for the body to be able to utilize it.

The most common form of ketoacidosis is probably diabetic ketoacidosis, in which blood glucose levels are high, but the glucose cannot get into the cells and be used, so fats are broken down for energy. At the height of a ketoacidosis, roughly 70% of the ketones in the body will be in the form of BOHB. This has implications for what we measure and for the monitoring of the treatment of ketoacidotic crises. UA dipstick ketones measure acetoacetate, and some will also detect acetone. None of the available UA methods measure BOHB. Thus, ketones measured in a UA will rise as ketoacidosis occurs, drop at the height of ketoacidosis as they are converted to BOHB, and then rise again as the condition is resolving and BOHB is converted back to Acac. A high Acac will occur both at the beginning and toward the end of the ketoacidosis, and Acac may actually be low at the height of a ketoacidotic crisis. BOHB on the other hand rises as the crisis evolves and drops as the crisis is resolved. The best test for following the resolution of a ketoacidotic crisis is repeat BOHB measurements.

BOHB is generally measured enzymatically on blood samples. BOHB response is maximal about 3 hours after glucose peaks. For example in a diabetic ketoacidosis, the peak BOHB will occur about 3 hours after the glucose peaks and in a normal patient given a glucose load, the BOHB will be lowest about 3 hours after the glucose peaks. During resolution of ketosis BOHB decreasing by half about every four hours as long as no more ketones are being produced. The test for BOHB is most commonly performed quantitatively using a kit adapted to the open channel on a chemistry analyzer. A point of care analyzer is also now available for BOHB.

Measuring ketones is most commonly used to monitor ketoacidosis, but ketone measurement can also be helpful in the differential diagnosis of some inborn errors of metabolism. For example, in fasting states, ketones should be elevated. If they are not, it can be an indication of disorders in fatty acid metabolism, or ketone metabolism itself. Additionally, in hyperammonemia states, the absence of ketones and acidosis indicates a urea cycle defect. Their presence suggests an organic acid disorder. Thus measuring ketones has multiple uses in medicine.

-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.

Tandem Mass Spectrometry in the Clinical Lab

Tandem mass spectrometry (MS/MS) is a methodology with so much versatility that new usages and applications seem to arise daily. MS/MS began as strictly a research tool, but over the last 20+ years it has made its way firmly into the clinical laboratory. The basic start of that transition came roughly 20 years ago when MS/MS assays were developed that allowed multiple intermediates of metabolism to be identified and quantified using a single punch from a dried blood spot. That development with this technology revolutionized newborn screening in the US over the next decade. Since then, more and more clinical uses for MS/MS have been recognized and developed.

Watching the growth of clinical MS/MS assays in hospital labs has been fascinating. As a reflection of this clinical emergence, journal articles containing MS/MS have increased in number over the same time period. For example, in 1998 the first MS/MS article appeared in the journal, Clinical Biochemistry. Between 1998 and 2003, 0 – 2 MS/MS articles were published each year, but from 2004-2007 that number was in the teens. From 2008-2010 more than 25 articles each year contained MS/MS technology, and from 2011 – 2013 that number ranged from 35-55 MS/MS-containing articles per year.

Initially, clinical applications using MS/MS were for limited assays, including newborn screening, confirmatory testing for inborn errors of metabolism (IEM), and for specific drugs, especially the immunosuppressant drugs. Testing quickly grew beyond drugs and toxicology using MS/MS methods, as the versatility of this testing became apparent. Assays began appearing for accurate measurement of Vitamin D, thyroid hormones and steroid hormones, to name only a few. In addition most MS/MS methods are sensitive enough that sample volumes requirements are small, or the assay can be performed using dried blood spots. Also, the ability to multiplex and measure multiple analytes in a single sample added to the utility of this methodology. Examples include 5 steroid hormones, 30+ analytes for IEM diagnosis or 200+ analytes for toxicology screening, all of which can be analyzed in a single sample within a short period of time.

As common as MS/MS assays now are in clinical laboratories, like early PCR technology, they have remained mostly manual tests run in specialized sections of the lab. They have required technical expertise and a love of hands-on, manual bench work. That is beginning to change with the advent of MS/MS instruments for bacterial identification and the entrance of MS/MS into the microbiology lab. This was the first MS/MS developed for a single, dedicated purpose and intended to require minimal manual intervention, either with day-to-day operation, or with maintenance and troubleshooting. This development clearly demonstrated that MS/MS can begin to approach the more plug-n-play type of technology needed for more fast-paced clinical labs. Developments like this will allow MS/MS to be integrated into more automated labs and ensures its future in the clinical laboratory.

-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.