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

Background: Non-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.

Methods: EDTA-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 50μL whole blood via a fixed-volume pipettor to either FP or DMS. Dried bloodspot areas were determined by image analysis.

Results: Hematocrits (HCT) were normally distributed (HCT=30.9±5.3%). For both FP and DMS, bloodspot areas (a, cm(2)) across patients were normally distributed: for FP, a=1.11±0.056cm(2) (±5.0%); for DMS, a=0.378±0.037cm(2) (±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).

Conclusions: Interpatient 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 (r(2)<0.65).