Heparin and partial thromboplastin time: an international survey

The reliability of routine partial thromboplastin time (PTT) methods in the measurement of the anticoagulant effect of heparin has been assessed in a study involving over 300 hospitals in the U.S. and overseas. Commercial PTT methods were relatively insensitive to heparin, added in vitro, compared with the standardized PTT method tested by the same laboratories. Non-commercial, locally-prepared reagents compared well with the standardized method particularly in the detection of a low concentration of heparin. The value of a sensitive reference preparation for the calibration of routine PTT reagents used in heparin control is demonstrated.