Laboratory monitoring of heparin. Effect of reagents and instruments on the activated partial thromboplastin time.

The CAP Hematology Survey of 1979-1980 included specimens with heparin levels between 0.0 and 0.8 U/ml. The results obtained with different reagent-instrument systems in common usage were analyzed. Sensitivity to heparin was dependent upon choice of reagent and did not appear to be influenced by choice of instrument. All systems displayed a loss of precision with increasing APTT which was independent of the choice of reagent. Compared to the photo-optical instruments, the BBL Fibrometer showed a greater loss of precision with longer APTT's. The results are discussed in terms of their effect on the laboratory's ability to adequately monitor heparin therapy.