Another Blow for Fingerprick Diagnostics
The demand for simple, point-of-care fingerprick testing is growing, but could a study highlighting drop-to-drop sample variation throw a spanner in the works?
DNA Medical Institute. Genalyte. And perhaps most famously (or infamously), Theranos. What do these companies have in common? All are developing technologies that rely on a simple fingerprick blood draw to provide quick and easy diagnostic testing. But now, along with the recent questions raised over what Theranos “nanotainer” technology is truly capable of (1), comes a study that casts doubt on the accuracy of results gained from fingerprick blood, regardless of the technology used to obtain and process it.
Two bioengineers from Rice University, Texas, USA, decided to investigate the drop-to-drop variation in results when using fingerprick blood for whole blood count testing. And their initial findings could spell trouble for test developers: the amount of variation in repeated samples of fingerprick blood was higher than for successive drops of venous blood. For example, the average percentage coefficient of variation observed measuring platelets in venous blood was 4.6–4.8 percent, whereas for fingerprick blood, it was 19 percent – a significantly larger difference. Higher levels of variation were also observed for lymphocyte counts, granulocyte counts, and hemoglobin measurements (2). “In one donor, the hemoglobin concentration could change by 2 g/dL in just two drops of blood. This suggests caution should be exercised by groups developing tests to analyze tiny drops of blood, and to clinicians interpreting the results from such tests,” says Meaghan Bond, first author of the study.
Complete blood count is one of the most common lab tests performed worldwide, and with increasing demand for point-of-care tests that use small amounts of blood, these findings have wide implications for the clinical community, adds Bond. However the issue isn’t necessarily with the point-of-care technologies themselves, but could be down to the fact that samples contain extracellular fluid as well as blood, which may skew results.
But the news isn’t all bad for researchers and startups hoping to harness fingerprick technology. Qualitative tests that provide a ‘yes’ or ‘no’ answer are less likely to be affected in cases where there is a high enough concentration of the studied analyte present in the blood. The authors also provide three recommendations for researchers working with fingerprick blood samples:
- Accept the inaccuracy of fingerprick blood as a trade-off for easy blood collection
- Collect, read, and average multiple drops (the study data suggests 80 µL is required) of blood to improve accuracy (though this requires more cost and time)
- When high accuracy is required, collect and analyze venous blood.
The team now plans to continue its investigation by testing the drop-by-drop variation of non-cellular blood components, such as glucose.
- R McGuigan, “Theranos: Science Fact or Science Fiction?”, The Pathologist, 13, 9 (2015). Available at: tp.txp.to/issues/1015/202
- MM Bond, RR Richards-Kortum, “Drop-to-drop variation in the cellular components of fingerprick blood: implications for point-of-care diagnostic development”, Am J Pathol, 144 (2015). PMID: 26572995.
I have an extensive academic background in the life sciences, having studied forensic biology and human medical genetics in my time at Strathclyde and Glasgow Universities. My research, data presentation and bioinformatics skills plus my ‘wet lab’ experience have been a superb grounding for my role as an Associate Editor at Texere Publishing. The job allows me to utilize my hard-learned academic skills and experience in my current position within an exciting and contemporary publishing company.