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Establishing a Therapeutic Range for Heparin Therapy

Patrick Brill-Edwards, MD; Jeffrey S. Ginsberg, MD; Marilyn Johnston, ART; and Jack Hirsh, MD
[+] Article and Author Information

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.


Copyright 2004 by the American College of Physicians


Ann Intern Med. 1993;119(2):104-109. doi:10.7326/0003-4819-119-2-199307150-00002
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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.

Figures

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Figure 1.
Therapeutic ranges for Dade Actin FS (top panel) and Ortho Activated Thrombofax (bottom panel) activated partial thromboplastin time (aPT) reagents.dotted lines

The therapeutic range of aPT values is determined by the points ( ) on the regression line (solid line) that correspond to the protamine titration heparin level of 0.2 to 0.4 U/mL. See Methods for manufacturing information.

Grahic Jump Location
Grahic Jump Location
Figure 2.
A comparison of regression lines describing the relation between the activated partial thromboplastin time (aPT) and heparin levels for Dade Actin FS reagents over several years.PPP

The slopes of the regression lines are similar ( > 0.2). The intercepts for lots 13 (1984), 102 (1988), and 129 (1991) are similar ( > 0.2), but the intercept for lot 154 (1991) differs from the other lots ( < 0.001). See Methods for manufacturing information.

Grahic Jump Location
Grahic Jump Location
Figure 3.
Comparison of the regression lines describing the relation between the activated partial thromboplastin time (aPT) and heparin levels for various manufacturers' reagents.PP

The slopes of the regression lines differ ( = 0.009), as do the intercepts ( < 0.001), among the various manufacturers' reagents. See Methods for manufacturing information.

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