Blood Test Results Vary From Drop To Drop

According to a new study published in the American Journal of Clinical Pathology, healthcare providers should be wary of drawing conclusions based on test results from a single drop of blood. As many diagnostic tests now rely on just one drop of blood from a finger prick, the researchers involved in the study caution that results from six to nine drops of blood should be combined in order to get an accurate result.

The research was conducted by Rebecca Richards-Kortum, a professor of bioengineering and of electrical and computer engineering, and Meaghan Bond, a student in Richards-Kortum’s lab at Rice University in Houston, Texas. The main finding of the study is that various measurements – including the amount of hemoglobin, platelets and white blood cells – varied significantly from drop to drop, when the blood was taken from a pin prick of the finger.

The researchers say these findings are significant because of the increasing prevalence of diagnostic devices that use a single drop of blood to diagnose certain conditions. Richards-Kortum and Bond made the discovery while trying to develop inexpensive blood tests for anemia, white blood cell and platelet counts.

While the most accurate way to qualify blood based on these measures is to draw blood from a vein and send it to a lab, this is not always possible in low-resource areas and situations where results are needed immediately. In these circumstances, healthcare providers reply much more heavily on finger prick tests.

While testing the accuracy of some newly-developed diagnostic tools based on finger prick blood, Bond noted a variation in the results recorded from hospital-grade blood analysis machines. In order to determine if the variation was a product of the experimental design – or truly differences in the levels of various blood components – the researchers began a study using blood collected from 11 donors.

Six 20 microliter droplets of blood were collected from each donor, in close succession. The researchers noted that they followed best practices when collecting the samples, including discarding the first drop of blood to eliminate traces of disinfectant, and refraining from squeezing the finger to force a larger volume of blood to be extracted.

As a control, the researchers used blood drawn from each of the donors’ veins to compare levels of blood components. The also used a separate set of blood donors to determine the optimal blood droplet size.

Richards-Kortum and Bond found that white blood cell count, platelet count and hemoglobin content varied significantly from drop to drop of blood collected from a single donor. “In some donors, the hemoglobin concentration changed by more than two grams per deciliter in the span of two successive drops of blood,” said Bond.

She also points out that the way in which the blood is collected from a finger prick can also affect results. She stressed the importance that healthcare providers know how to properly collect the blood and that multiple tests should be performed in order to confirm a result.

“Our results show that people need to take care to administer finger prick 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,” said Bond. While she understand the necessity for finger prick tests in low-resource settings, she says the results of the study indicate that six to nine droplet tests are necessary to produce a result consistent with those from a vein blood test.

Sources:

• Test results of fingerprick blood vary from drop to drop – http://www.medicalnewstoday.com/articles/302785.php
• Bond, M and Richards-Kortum, R. (2015). Drop-to-Drop Variation in the Cellular Components of Fingerprick Blood. Implications for Point-of-Care Diagnostic Development. Am J Clin Pathol. 144, 885-894.