Summary
Heparin therapy was monitored with the activated partial thromboplastin time (APTT)
and with chromogenic substrate assays (factor Xa and factor Ha inhibition) in 100
plasma samples from 47 patients. Heparin concentrations were classified as being below,
within or above a defined therapeutic range (TR; 0.2-0.55 units heparin/ml). In a
first group of patients (A), all three assays allocated the plasma heparin levels
to the same concentration interval with respect to the TR. The most frequent diagnoses
in group A were uncomplicated arterial or venous thromboembolism, myocardial infarction
with limited tissue necrosis, cardiac surgery without major complications and successfully
treated infectious disease. In a second group of patients (B), the results of APTT
suggested higher heparin concentrations with respect to the TR than the chromogenic
assays. Predominant diagnoses were severe infectious diseases, severe liver disorders,
extensive myocardial infarction and postoperative complications after cardiac surgery.
The discrepancy between heparin concentrations determined by either APTT or the chromogenic
substrate assays is most likely due to a non-heparin related prolongation of APTT
caused by the underlying disease.
Keywords
Heparin therapy - Heparin monitoring - Chromogenic substrate assays - Activated partial
thromboplastin time - Acquired coagulation disorders
