The effect of heparin on the activated partial thromboplastin time.

Data from the 1976 and 1977 CAP surveys were analyzed for response of the activated partial thromboplastin time (APTT) to heparin. Different sources and concentrations of heparin were used. The results indicate that the precision of the APTT is more dependent on instrumentation than on partial thromboplastin. This was true for all four of the heparinized specimens evaluated. A single exception was found with the "old" Dade reagent activated cephaloplastin. The mean difference in the activated partial thromboplastin times obtained with differing concentrations of heparin was entirely dependent on the partial thromboplastin reagent used. No significant difference in the results was found when equal concentrations of bovine lung and porcine intestinal mucosal heparin were compared.