Standardization of the activated partial thromboplastin time for monitoring of heparin therapy: where should we go?

Standardization of the APTT for monitoring of heparin therapy is needed urgently. On the one hand, reference materials and methods should be established. On the other hand, the scale for reporting of results should be standardized. The implementation of a system based on a reference APTT method meets a number of practical problems. The use of lyophilized plasma as a reference material is of questionable value, until these products more satisfactorily resemble fresh patient plasma specimens.