ABSTRACT
Although the relationship between plasma heparin concentration and APTT is ap proximately linear over the therapeutic range, the reagents used to measure APTT vary from one laboratory to another, so that the same concentration of heparin can be associated with different APTT values. Ideally, the range of APTT values corresponding to 0.2-0.4 U/mL of heparin for each laboratory should be used to monitor therapy.
