Comparing methods of establishing the aPTT therapeutic range of heparin

The American College of Chest Physicians (ACCP) recommends that the activated partial thromboplastin time (aPTT) therapeutic range for unfractionated heparin be defined as the aPTT corresponding to a heparin concentration of 0.3-0.7 micro/mL by heparin anti-factor Xa assay. This recommendation suggests that a therapeutic range defined in this manner should be superior to traditional empiric therapeutic ranges of 1.5-2.5 times the control. A pilot study was conducted to evaluate the ACCP recommendation for heparin monitoring.

To compare heparin dosage adjustments guided by a heparin concentration-derived therapeutic range (HCDTR) with those influenced by traditional empiric therapeutic ranges for the aPTT.

This study was conducted in 2 phases. In phase 1, the various aPTT therapeutic ranges were established and/or defined. The first empiric therapeutic range (E1) was established by performing an aPTT test on healthy volunteers. This E1 was defined as 1.5-2.5 times the mean normal aPTT. A second empiric therapeutic range (E2) was defined as 1.5-2.5 times the patient's baseline aPTT. The aPTT HCDTR had been defined in a previous study as 48-61 seconds. In phase 2, heparin dosage adjustment decisions guided by each empiric range and the HCDTR for the aPTT were compared with heparin dosage adjustment decisions guided by actual heparin concentrations. Decisions were in agreement when both the aPTT result and plasma heparin concentration indicated the same dosage change. Forty patients had a bedside aPTT determined prior to receiving continuous infusion heparin and again within 48 hours of heparin initiation. Plasma heparin concentration by anti-factor Xa assay was performed on the blood samples obtained after heparin initiation. Heparin dosage adjustment decisions were evaluated by determining the agreement of each aPTT test result with the corresponding plasma heparin concentration. An overall level of agreement (defined as the % of decisions that were in agreement) for each aPTT therapeutic range was determined.

The level of agreement in dosage adjustment decisions between heparin concentration and E1, E2, and HCDTR was 28/40 (70%), 28/39 (72%), and 23/40 (58%), respectively (p = 0.34). Heparin dosage adjustment decisions based on an aPTT HCDTR did not significantly differ from heparin dosage adjustment decisions guided by traditional empiric therapeutic ranges for a bedside aPTT.

This pilot study showed similar heparin dosage adjustment decisions using an empiric aPTT therapeutic range versus a heparin concentration-derived aPTT therapeutic range.