Limitations of the Activated Partial Thromboplastin Time for Determination of Plasma Heparin Concentration and Half-Life in Human Subjects

Summary

In vivo heparin concentrations and half-life were estimated in 20 human subjects, after a single intravenous injection.

The method, used for heparin determination, is based on the activated partial thromboplastin time. The test plasmas are diluted in plasma of the same subject obtained before heparin administration. In this way the heparin concentrations are reduced to measurable levels between 0.1 I. U./ml and 0.8 I. U./ml. Indeed a linear relationship between log activated partial thromboplastin time and heparin concentrations from 0.1 to 0.8 I. U./ml can be computed. Different half-lives were found in 13 of the 20 subjects examined when different dilution factors were used. This seems an important limitation for the examination of the pharmacokinetics of heparin.

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