The aPTT assay as a monitor of heparin anticoagulation efficacy in clinical settings

Activated partial thromboplastin time (aPTT) and prothrombin time (PT) are 2 major methods of screening patients for bleeding tendency. Heparin is an anticoagulant commonly used for various clinical conditions and will thus affect the coagulation profile. The influence of heparin on PT vs aPTT, seldom addressed in the past, should be carefully investigated. Prospective data on 35 patients who were heparinized for clinically indicated conditions were collected and analyzed for the change in PT (dPT) and aPTT (daPTT) at 3 time points after treatment, all of which were compared with baseline data checked before therapy. Age, sex, and the results of a complete blood count and liver and renal function tests were also evaluated for each patient to determine their effects on dPT and daPTT. The therapeutic goal of keeping the aPTT within a desirable range was achieved in ∼75% of patients by the last day of heparin therapy. Within this range, dPTs were not statistically significant, nor was the effect of age, sex, hemoglobin level, serum albumin level, white cell count, platelet count, or renal or hepatic function. In patients with thrombosis, dPT was not significantly influenced by heparin dose. During an overlap in the periods of coumadin and heparin administration, PT was used as a guide for adjusting the coumadin dose. The anticoagulant effect, indicated by a PT in the target range, would occur primarily secondary to coumadin administration and would make it relatively easy to decide when to discontinue heparin.