How Meaningful are Results of Testing a Drop of Blood?

With Theranos’ recent announcement of its transition away from laboratory operations toward technology development, a study released last year regarding variability of test results from a single drop of blood remains timely. The study, published in the American Journal of Clinical Pathology, addressed variation between successive drops of fingerprick blood—suggesting that deviation may be even greater than the variation between fingerprick and venous blood samples. As a result, the authors say, tests may need to be run on six to nine drops of blood, rather than one. This study’s findings could pose a problem for clinical decisions based on fingerprick tests, like anemia testing, and it could impact the future development of point-of-care diagnostics—it was also often cited as questions were raised about the capabilities of Theranos’ micro-sample technology.

“These data suggest caution when using measurements from a single drop of fingerprick blood,” writes co-author Rebecca R. Richards-Kortum, Ph.D., from Rice University in Houston. “Our results show that people need to take care to administer fingerprick tests in a way that produces accurate results because accuracy in these tests is increasingly important for diagnosing conditions like anemia, infections and sickle-cell anemia, malaria, HIV and other diseases.” Fingerpicks are often used in point-of-care testing and are preferred over venipuncture because of patients’ dislike of needles. Over the years, many tests have addressed the accuracy of results obtained from fingerstick samples versus venous blood, but few have assessed the variation in results between the successive drops of blood obtained from one fingerprick. “A growing number of clinically important tests are performed using fingerprick blood,” co-author Meaghan Bond, said in a statement. “It is important to understand how variations in fingerprick blood collection protocols can affect point-of-care test accuracy as well as how results might vary between different kinds of point-of-care tests that use fingerprick blood from the same patient.” For more detailed discussion of this study and the researchers recommendations see the December 2015 issue of Diagnostic Testing & Emerging Technologies.