Establishing a Therapeutic Range for Heparin Therapy

doi:10.1059/0003-4819-119-2-199307150-00002

Establishing a Therapeutic Range for Heparin Therapy

From McMaster University Medical Center and Hamilton Civic Hospitals Research Centre, Hamilton, Ontario, Canada. Requests for Reprints: Dr. P. Brill-Edwards, MD, McMaster University Medical Center, 1200 Main Street West, HSC-3W12, Hamilton, Ontario L8N 3Z5, Canada. Acknowledgments: The authors thank Dianne Donovan, RN, Robin Roberts, PhD, and David Sackett, MD, for their contributions to and support of this study. Grant Support: Dr. Ginsberg is the recipient of a Research Scholarship of the Heart and Stroke Foundation of Canada. Dr. Hirsh is a Distinguished Research Professor of the Heart and Stroke Foundation of Canada and a Trillium Award Recipient of the Ministry of Health.

Abstract

Objective: To compare two methods of determining a therapeutic range of activated partial thromboplastin time (aPT) results.

Design: Cohort studies.

Setting: Referral teaching hospital.

Patients: Inpatients who received unfractionated heparin intravenously for venous thromboembolic disease.

Measurements: A therapeutic range determined by aPT ratios of 1.5 to 2.5 times the control value as compared with a therapeutic range determined by protamine titration heparin levels of 0.2 to 0.4 U/mL.

Results: For all aPT reagents studied, a ratio of 1.5 times the control value is much less than a minimum protamine titration heparin level of 0.2 U/mL. Various manufacturers' aPT reagents and reagent lots from the same manufacturer show considerable variation in response to heparin and therefore have different therapeutic ranges.

Conclusions: A different dose of heparin would be required to produce an aPT ratio of 1.5 times the control value, depending on the reagent used. Establishing a therapeutic range for aPT results using protamine titration heparin levels of 0.2 to 0.4 U/mL as a reference standard is practical and compensates for the variable response of aPT reagents to heparin.