Heparin Therapy Monitoring Tests – Effects of Method and Patient Variables upon Accuracy

Tests utilizing the recalcification time of whole blood or plasma (e.g. A. P. T. T.) to monitor heparin therapy of a patient with malignancy and an accompanying thrombotic disorder, are subject to unpredictable in-vitro changes which occur during the time interval between withdrawal of blood from the patient and eventual testing in the laboratory. Significant reduction or prolongation of clotting time occurs in as little as five minutes, necessitating the performance of the test (whole blood recalcification or alternately centrifrigation and plasma recalcification) as rapidly as possible after patient contact.

Correlations are presented between the direction and magnitude of these time-related changes and methodology variables (venipuncture stress, tube surface, decalcifying agent, storage temperature) as well as patient variables (heparin dosage, PF-4 activity, clotting factor lability, heparin tolerance). Repeated testing of the same blood samples may provide a, pattern of change which reflects in-vivo heparin catabolism.