Establishing a therapeutic range for heparin therapy.
OBJECTIVE
To compare two methods of determining a therapeutic range of activated partial thromboplastin time (aPTT) results.


METHODS
Cohort studies.


METHODS
Referral teaching hospital.


METHODS
Inpatients who received unfractionated heparin intravenously for venous thromboembolic disease.


METHODS
A therapeutic range determined by aPTT 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 aPTT 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' aPTT 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 aPTT ratio of 1.5 times the control value, depending on the reagent used. Establishing a therapeutic range for aPTT 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 aPTT reagents to heparin.
McMaster University Medical Center, Hamilton, Ontario, Canada.
P
P
Brill-Edwards
J S
JS
Ginsberg
M
M
Johnston
J
J
Hirsh
D015331:Cohort Studies; D004305:Dose-Response Relationship, Drug; D006493:Heparin / Q000008:administration & dosage* / Q000097:blood; D006801:Humans; D007202:Indicators and Reagents; D010314:Partial Thromboplastin Time; D012016:Reference Values; D012044:Regression Analysis; D013923:Thromboembolism / Q000097:blood / Q000188:drug therapy; D017186:Titrimetry
D007202:Indicators and Reagents; D006493:Heparin