overcoming hematocrit accuracy issues: VAMS vs. DBS
by Neoteryx Microsampling on Mar 6, 2018 1:32:52 PM
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 with DBS or other blood microsampling technologies and get results on par with those generated from wet blood?
Volumetric Microsampling Overcomes the Hematocrit Bias
A breakthrough in medical technology, volumetric absorptive microsampling improves the the DBS approach to microsampling by enabling the collection of a fixed volume of blood. Volumetric microsampling can also reduce the costs of blood sample handling and shipping, because the collected specimens are dried blood samples that remain viable at ambient temperatures.
Mitra® devices with patented VAMS® technology makes it possible to draw fixed volume blood samples of 10, 20 and 30 µL (microliters) from a single finger prick. This method is less invasive than venipuncture methods that draw 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 conventional venipuncture sampling. With DBS, a drop of blood drawn from the infant’s finger or heel is placed on a specially treated filter paper (Guthrie or Whatman) or card for analysis.
Similarly, a Mitra® device with its absorptive VAMS® tip enables a quick blood draw with a finger-stick using a small lancet. The resulting microsamples will be processed as a type of DBS sample, requiring 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, a blood spot is placed on a filter card and allowed to spread. How far the blood sample spreads will depend on the viscosity of the blood. If the blood spreads slowly, the viscosity is higher. If it spreads quickly, the viscosity is lower as 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, or more hydrated blood samples, spread further across the dried blood paper. In the lab, when the target blood sample area is punched from the DBS sample card, the analysis can result in a lower percentage of red blood cells or hematocrit. Smaller, more viscous samples will show a comparatively higher hematocrit level. These variations between samples can cause inconsistencies in the analytical data.
As a solution, perforating the DBS cards or adding wax to the DBS cards had the effect of limiting the blood spreading and better defining the area the spot covers. This results in a fixed volume and more accurate hematocrit level reading. The first method is called “whole spot analysis, perforated, and precut.” The second method is called "patterned DBS, or "pDBS."
But the best innovation 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. The Mitra device with a VAMS tip absorbs a precise volume of blood 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.
Also, dried blood microsamples do not require refrigeration or special handling. The Mitra device is designed for easy sampling by anyone, anywhere. For many research studies, participants have successfully self-collected their samples at home or in other remote locations.
In the laboratory, sophisticated equipment and techniques can analyze microsamples as accurately as liquid blood samples or larger specimen samples.