Quantification of Unfractionated Heparin in Human Plasma and Whole Blood by Means of Novel Fluorogenic Anti-FXa Assays

Novel and sensitive plate-based fluorogenic anti-factor Xa (FXa) assays were investigated to quantify unfractionated heparin (UFH) in human plasma and whole blood within the therapeutic ranges of 0–1.6 U/mL and 0–0.8 U/mL, respectively. Two fluorogenic anti-FXa assay methods were defined for low (0–0.6 U/mL) and high (0.6–1.2 U/mL) pharmacologically relevant UFH concentration ranges in pooled human plasma. In both cases significant differences were observed at intervals of 0.2 U/mL (P \u3c 0.05). The semi-logarithmic plots of the calibration curves in the low and high UFH range were both fitted to linear regressions with correlation coefficients of 0.96 and \u3e0.99, respectively. The assay was also optimized for whole blood which was capable of differentiating UFH concentrations at intervals of 0.2 U/mL (P \u3c 0.05) in the range of 0–0.4 U/mL. The statistically different results were fitted to a linear regression with a correlation coefficient of \u3e0.99. The results obtained in this study could assist diagnostic laboratories towards improved monitoring of UFH therapy