In addition to being patient-friendly, fingerprick blood tests are an important tool for health care providers. They frequently used in point-of-care and low-resource settings.
However, a Rice University study has found that fingerprick test results can vary significantly from drop to drop. The researchers say that at least six to nine drops of blood are necessary for consistent measurements of hemoglobin, white blood cells and platelets.
Fingersticks are generally performed on children and the elderly, when only a small amount of blood (less than 500 μg) would suffice for the test. Examples of tests which use capillary blood samples are those to measure blood sugar, mononucleosis, hemoglobin levels, and genetic testing.
The Rice University researchers examined the variation between blood drops drawn from a single fingerprick and found that results were not consistent. This led them to conclude that health care professionals must take care to avoid skewed results as they design new protocols and technologies that rely on fingerprick blood.
Six successive 20-microliter droplets of blood were drawn from 11 donors. To determine whether minimum droplet size might also affect the results, 10 successive 10-microliter droplets were taken from seven additional donors. All droplets were drawn from the same fingerprick and the researchers followed best practices in obtaining the droplets – the first drop was wiped away to remove contamination from disinfectants, and the finger was not squeezed to avoid inaccurate results. For experimental controls, venipuncture was used to draw tubes of blood from an arm vein.
While each 20-microliter droplet was analyzed with a hospital-grade blood analyzer for hemoglobin concentration, total WBC count, platelet count and three-part WBC differential, each 10-microliter droplet was tested for hemoglobin concentration with a popular point-of-care blood analyzer used in many clinics and blood centers.
It was found that hemoglobin content, platelet count and WBC count each varied significantly from drop to drop. The researchers found that averaging the results of the droplet tests could produce results that were on par with venous blood tests, but that tests on six to nine drops blood were needed to produce consistent results.
According to the RICE University news report, the lead author of the said, “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.”