Dried Blood Spots – Sample Extraordinaire

When you mention dried blood spot samples (DBS), most people think of newborn screening. That’s natural because the most common usage for DBS is newborn screening. However, DBS samples are actually one of the most versatile, stable and easily stored samples that it’s possible to collect from a human. And did I mention useful?

To create a DBS sample, whole blood, often from a finger or heelstick, is spotted onto a very specific weight of filter paper. The weight and type of filter paper is important so that all DBS are created equally, and so that differences in testing are not introduced due to filter paper differences. Enough blood is used to thoroughly saturate the paper (in most case roughly 50 uL will saturate the marked dot) and then the blood spot is allowed to dry completely.

DBS are ideal samples for population based testing. The list of positive attributes is long. They are easily obtainable (fingerstick). They use very little blood (50-60 uL). Once dried they are not subject to the sample degradation effects that plague liquid samples. They are simple to transport with no possibility of spilling or breaking. They store easily, taking up very little space, and studies suggest that once dried, the sample is stable for years, whether at room temperature, refrigerated or frozen.

In addition to these obvious benefits, a truly remarkable number of analytes can be measured from one or two 6 mm punches out of a dried blood spot, with a punch containing roughly 10 uL of blood. Protein enzymes are generally stable in a dried blood spot, allowing enzyme activity to be measured from DBS. Viruses such as HIV can be measured in DBS. Even RNA and DNA is stable in these spots, as evidenced by the PCR assays that are being performed using them. These assays include such things are Cystic Fibrosis (CF) mutation testing and screening for severe combined immunodeficiency (SCID).

Besides the PCR testing for CF and SCID, the newborn screen itself uses the DBS sample to measure some or all of the following: either T4 or TSH for hypo- or hyperthyroidism, hemoglobin variants for sickle cell anemia, 17-hydroxyprogesterone for congenital adrenal hyperplasia, immunoreactive trypsinogen for CF, amino acids and acylcarnitines for amino acid, fatty acid and organic acid disorders, and an enzyme for galactosemia. Each one of these assays is performed using the single punch from a DBS. The DBS is an almost overlooked sample type. However it has the potential to be used for a huge variety of testing.

 

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-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.

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