title: Drop-to-drop variation in the cellular components of fingerprick blood: implications for point-of-care diagnostic development.
abstract: OBJECTIVE
  Blood obtained via fingerprick is commonly used in point-of-care assays, but few studies have assessed variability in parameters obtained from successive drops of fingerprick blood, which may cause problems for clinical decision making and for assessing accuracy of point-of-care tests.
  
  
  METHODS
  We used a hematology analyzer to analyze the hemoglobin concentration, total WBC count, three-part WBC differential, and platelet count in six successive drops of blood collected from one fingerprick from each of 11 donors, and we used a hemoglobinometer to measure the hemoglobin concentration of 10 drops of fingerprick blood from each of 7 donors.
  
  
  RESULTS
  The average percent coefficient of variation (CV) for successive drops of fingerprick blood was higher by up to 3.4 times for hemoglobin, 5.7 times for WBC count, 3 times for lymphocyte count, 7.7 times for granulocyte count, and 4 times for platelets than in venous controls measured using a hematology analyzer. The average percent CV for fingerprick blood was up to 5 times higher for hemoglobin than venous blood measured using a point-of-care hemoglobinometer. Fluctuations in blood parameters with increasing volume of fingerprick blood are within instrument variability for volumes equal to or greater than 60 to 100 μL.
  
  
  CONCLUSIONS
  These data suggest caution when using measurements from a single drop of fingerprick blood.
authors.affiliation: From the Department of Bioengineering, Rice University, Houston, TX.
authors.forename: Meaghan M
authors.initials: MM
authors.lastname: Bond
authors.affiliation: From the Department of Bioengineering, Rice University, Houston, TX. rkortum@rice.edu.
authors.forename: Rebecca R
authors.initials: RR
authors.lastname: Richards-Kortum
mesh_terms: D001800:Blood Specimen Collection / Q000592:standards*; D005385:Fingers; D006403:Hematologic Tests / Q000592:standards*; D006801:Humans; D010865:Pilot Projects; D019095:Point-of-Care Systems / Q000592:standards*; D015203:Reproducibility of Results
keywords: Capillary blood; Fingerprick blood; Fingerstick blood; Hemoglobin; Point-of-care diagnostics; WBC