Thrombin generation for the control of heparin treatment, comparison with the activated partial thromboplastin time.

Heparin can be quantified with antifactor Xa and IIa tests (aXa, aIIa) but the anticoagulant power of heparin depends upon plasma properties as well as upon heparin concentrations and thus differs between subjects. Measuring the effect, as with the activated partial thromboplastin time (APTT) therefore is clinically more relevant. Here we investigate the use of the endogenous thrombin potential (ETP) for this purpose. In 12 volunteers 9000 IU of four heparins of different mol. wt distributions were injected. Samples were taken at 11 time points between 0 and 24 h. With the exception of the 0 and 24-h time points, heparin could be demonstrated by its aIIa and aXa activity in virtually all samples. The APTT showed the effect of this heparin in 34% of the samples; the ETP in 80%. This is partly due to the wide margins of the normal values, caused by large interindividual variation [coefficient of variation (CV) approximately 12% for the APTT, approximately 17% for the ETP]. The intraindividual variation is much smaller (CV approximately 4% for the APTT, approximately 5% for the ETP). Relative to the baseline value of the individual, the heparin effect was recognized by the APTT in 55% of the cases and by the ETP in 98%. There were no large differences between the different types of heparin.