DBS and the hematocrit bias: a brief introduction

For decades, Dried Blood Spot (DBS) cards have served as a useful alternative to painful venipuncture blood draws, especially for infants and other vulnerable patients or study subjects.

Because DBS delivers dried samples that don't require cold-chain shipping or cold storage, this method has also helped reduce costs and the other hassles associated with liquid blood collection and transport. However, DBS technologies have their own problems or limitations, which that have hindered widespread adoption of DBS cards and filter papers.

Limitations of DBS Cards

Chief among the limitations or drawbacks of DBS cards is the "hematocrit bias," also known as the "hematocrit effect."

Hematocrit is, in short, the volume percentage of red blood cells in a blood sample. Viscosity determines how well the blood spreads on the filter paper used in DBS. Blood hematocrit generally has an inverse relationship to the spread. Blood with a high hematocrit level results in a smaller dried blood sample, and a low hematocrit level results in larger-size samples.

The hematocrit bias refers to the effect of this relationship on the quality and reliability of the blood samples and the data generated from them. A blood spot sample that spreads unevenly on a DBS card can easily lead to a disproportionate result.

A further limitation is that it can be difficult to extract the appropriate amount of the required analyte from the surface of the DBS card. Add to this the variations in paper quality, hole punching of the spots for extraction and analysis, among other factors, and you've got real problems in the lab.

In the past, when research labs or clinical labs encountered problems with DBS, it made more sense to just go back to traditional blood draws with venipuncture to collect a larger liquid blood sample for research studies, clinical trials and other projects. 

However, traditional venipuncture blood draws can deter people from participating in research studies or trials. Many people fear needles and find blood draws painful or stressful.

Now, there is a better way.

Microsampling Devices as DBS Alternatives

The Mitra^® device, based on volumetric absorptive microsampling technology, was created in a quest to solve for the limitations of conventional DBS technology in general, and the hematocrit bias in particular. Simply put, microsampling using VAMS^® technology takes the hematocrit bias out of the sampling equation.

With volumetric microsampling, a quantitative, volumetrically accurate sample can be easily collected anywhere, at any time, by almost anyone, yielding results that correlate to those from wet blood. Volumetric microsampling doubles down on the benefits of DBS while overcoming its limitations.

The hemaPEN^® is another volumetric sampling device that was designed to overcome the hematocrit bias. Considered a "precision DBS" sampling device, the hemaPEN combines glass capillary tubes with DBS filter paper in a single, portable device. The hemaPEN collects 4 volumetrically identical capillary samples from a single finger-stick, or a single source.

Click the "pen" shut and that action transfers the 4 capillary blood samples to 4 pre-punched DBS filter cards housed in a cartridge inside the device. All 4 samples are locked inside until the tamper-resistant hemaPEN reaches the lab for processing.

The hemaPEN overcomes the hematocrit bias with its precise DBS sampling design and eliminates the hole-punching step that is usually required with standard DBS cards in the lab. 

It's no wonder that lab directors who previously encountered DBS challenges are now adopting volumetric microsampling as the next-generation solution to dried blood sampling.