Interpatient distributions of bloodspot area per fixed volume of application: Comparison between filter paper and non-cellulose dried matrix spotting cards

• We examined interpatient distribution of bloodspot areas per fixed 50 μL volume of blood.
• We compared results between filter paper and non-cellulose dried matrix spotting (DMS) cards.
• Interpatient coefficient of variation of areas was 5.0% for filter paper, 9.9% for DMS cards.
• Areas correlated negatively with hematocrits for filter paper, but positively for DMS cards.
• Correlation of areas with hematocrits only partially explained interpatient variations in areas.

BackgroundNon-cellulose dried matrix spotting (DMS) cards are an alternative to filter paper (FP) for bloodspots. We compared the interpatient distributions of bloodspot areas between DMS and FP for a fixed volume of application of whole blood, and examined correlations of areas with hematocrit.MethodsEDTA-whole blood adult patient samples (n = 49; 25 males, 24 females) were utilized after routine measurement of hemoglobin and hematocrit. Replicate (4 ×) bloodspots were produced by bolus drop application of 50 μL whole blood via a fixed-volume pipettor to either FP or DMS. Dried bloodspot areas were determined by image analysis.ResultsHematocrits (HCT) were normally distributed (HCT = 30.9 ± 5.3%). For both FP and DMS, bloodspot areas (a, cm2) across patients were normally distributed: for FP, a = 1.11 ± 0.056 cm2 (± 5.0%); for DMS, a = 0.378 ± 0.037 cm2 (± 9.9%). Relative bloodspot area differences across the population range were > 20% for both DMS and FP. Correlation of bloodspot areas to hematocrit was negative for FP (r = − 0.80) but positive for DMS (r = + 0.78).ConclusionsInterpatient variation in blood volume per area is a preanalytical variable for both DMS and FP bloodspots. Hematocrit is but one interpatient variable, as correlations of fixed-volume bloodspot areas with hematocrit across patients were substantially inexact (r2 < 0.65).