the microsampling blog

overcoming hematocrit accuracy issues: VAMS vs. DBS

a DBS filter paper card next to the purple Mitra Cartridge blood sampler

Overcoming the hematocrit (HCT) effect has for years been a major challenge to widespread adoption of dried blood spot (DBS) sampling technology. Is there a way to overcome the hematocrit bias and get results on par with those generated from wet blood?

A breakthrough in medical technology, volumetric absorptive microsampling, improves the quality of healthcare for patients while cutting costs of blood sample handling and analysis. Drawing fixed volume blood samples of 20 microliters from a single finger prick is less invasive than venipuncture methods that extract blood volumes approximately one thousand times greater.

Hematocrit Accuracy in Dried Blood Spot Microsampling

Dried Blood Spot (DBS) sampling has been utilized for decades to assess the blood chemistry of infants whose blood supply will not support normal venipuncture sampling. A drop of blood drawn from the infant’s finger or heel is placed on a specially treated (Guthrie or Whitman) card for analysis. Similarly, a Mitra® device with the patented VAMS® tip is enabled by a finger-stick or heel-stick with a small lancet, and requires no refrigeration for storage and transport.

Lab analyses have shown that one critical variation exists in standard DBS evaluation: results of blood hematocrit levels, the volume of red blood cells as a percentage of the sample, can be misleading. With traditional DBS, blood is placed on a special card and allowed to spread. How far the blood sample spreads depends on the viscosity of the sample. If the blood spreads slowly, the viscosity is higher. If it spreads quickly, the blood is somewhat thinner.

The existing level of hematocrit analyzed in a sample may vary due to a patient’s body hydration level. Lower viscosity, more hydrated blood samples spread further across the dried blood paper. When the target blood sample area is punched from the sample card, the analysis tends to result in a lower percentage of red blood cells or hematocrit. Smaller, more viscous samples will show a comparatively higher hematocrit level.

As a solution, perforating the DBS cards had the effect of limiting the blood spreading by better defining the area the spot covers, resulting in a fixed volume and more accurate hematocrit level reading. The method is called “whole spot analysis, perforated, and precut.”

But the best was yet to come.

The VAMS Advantage

The VAMS method has emerged as the most promising solution yet to the problem of hematocrit bias in DBS sample collection. Using the Mitra device with a VAMS tip absorbs a precise volume of blood (20µ) without regard to the viscosity, within seconds. When the sample is dried, the remaining volume delivers an accurate hematocrit reading without the variability of DBS.

visual depictions of the various issues associated with DBs filter paper, next to a VAMS blood collection tip

Also, microsamples do not require refrigeration or special handling and can be self-administered easily from remote locations. At the laboratory, sophisticated equipment and techniques can evaluate microsamples as accurately as a larger specimen.

If you haven't yet explored the advantages of the latest microsampling technology, you can do it now, for free.

Click to download case studies that show the comparison between using traditional DBS cards and the Mitra blood collection device


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