Summary
The competitive binding assay described will specifically and accurately measure concentrations
of administered heparin in biological fluids with a sensitivity of 60 ng ml-1. Neither
endogenous glycosaminoglycans, nor plasma proteins such as ATIII and PF4 interfere
in the assay. Semi-synthetic highly sulphated heparinoids and LMW heparin can also
be measured. Using this assay heparin clearance followed simple first-order kinetics
over the dose range 100-5,000 units, but the half-life was strongly dose-dependent.
There was good correlation with heparin activity measurements by APTT and anti-Xa
clotting assays. Plasma concentrations were measurable for at least 5 h following
subcutaneous injection of 10,000 units of heparin. Excretion in the urine could be
followed after all but the lowest intravenous dose. This assay, used in conjunction
with measurements of heparin anticoagulant activity, will be valuable in the elucidation
of mechanisms of action of heparin and the heparinoids, and in the assessment and
management of problems related to heparin therapy.
Keywords
Heparin - Heparinoids - Competitive binding assay - Clearance - Volunteer studies
