A comparison of plasma pyridoxal 5'-phosphate concentrations in capillary (finger prick) and venous blood

The purpose of our study was to investigate the validity of using capillary blood plasma to estimate the pyridoxal 5'-phosphate (PLP) concentration of venous blood plasma. To accommodate the small volumes of capillary blood usually obtained, we modified the experimental conditions of the L-tyrosine apodecarboxylase (TDC) assay for PLP by increasing both the specific activity of 14C-tyrosine and the reaction incubation time. Plasma PLP concentrations determined by the TDC assay and the micro-modified TDC assay were highly correlated (r = 0.995, p = 4.0 X 10(-6)). Using the micro-modified TDC assay, we observed no significant difference between the plasma PLP concentrations of venous and capillary (finger prick) blood from 10 healthy adults. Thus, capillary blood plasma can be used to estimate the PLP concentration of venous blood plasma. This observation will aid in verifying data concerning the vitamin B-6 status assessment of individuals as determined by capillary blood plasma PLP concentrations.