Versatile, non-clotting-based heparin assay requiring no instrumentation

Abstract

A non-clotting-based heparin assay requiring no instrumentation has been developed by attaching protamine (a heparin antidote) to a porous filter paper strip and monitoring the subsequent capillary migration of heparin sample through the paper. The area of paper to which heparin adsorbed, which is proportional to the concentration of heparin in the sample, is made visible by spraying Methylene Blue NNX solution onto the paper strip when the sample reservoir has emptied. The dye interacts with heparin to cause a metachromatic shift of the dye's absorption maximum from blue to purple. Heparin concentrations in the samples are estimated according to the length of the purple region on the paper strip. Heparin in plasma (2 to 35 int. units/mL) can be differentiated in approximately 6 min. The plasma heparin values derived by the new method agree reasonably well with those obtained by conventional assays (r greater than 0.99, n = 48).