A study recently published in the American Journal of Clinical Pathology suggests blood counts obtained from a fingerstick may not be as reliable as we think. Researchers at Rice University’s department of Bioengineering collected six consecutive drops of fingerstick blood into separate containers from 11 donors. They also drew comparison samples from a vein in the arm (venipuncture) from each patient. Samples were tested for hemoglobin levels,WBC counts, differentials, and platelet counts.
For each subject, they recorded the test results from all six drops and measured the degree to which they varied. They also repeatedly tested blood from the tube of blood on the same subject and assessed its variability. All tests were performed on the same instrument. The difference between each fingerstick drop varied up to three times more than the difference between repeated testing from the tube of venous blood. Variability was 5.7 times greater for white blood counts (WBC), three times greater for lymphocyte counts, 7.7 times greater for granulocyte counts, and 4 times greater for platelets.
Hemoglobin measures the oxygen carrying capacity of the blood and is often used to assess anemia and the necessity for transfusion. WBC, lymphocyte and granulocyte counts determine the body’s cellular immune response and are often used to assess infection and leukemias.
The author of the study recommends caution when reporting and interpreting hemoglobin and WBC results for clinical decision-making when obtained by devices that use minute quantities of blood.