Substitution of a heparin correlation value for activated partial thromboplastin time in heparin nomograms

Purpose. Use of nomograms based on the "heparin correlation value" (HCV)-a value that corresponds to measured activated partial thromboplastin time (aPTT) and that removes the need to revise nomograms in response to a change in the aPTT reagent or coagulometer used-was evaluated as an alternative to traditional aPTT-based anticoagulation nomograms. Summary. Data were collected on patients receiving heparin therapy for selected indications (thrombotic disorders, cardiac conditions, and acute coronary syndromes) during four-month periods before (n = 59) and after (n = 60) implementation of the HCV-based nomograms. The primary endpoints were the rate at which coagulation laboratory measurements were obtained at the appropriate time and the rate of appropriate dosage adjustment in response to reported laboratory values; secondary endpoints included the time to attainment of the first target anticoagulation value. After implementation of HCV-based nomograms, coagulation laboratory measurements were obtained at the appropriate time in (mean +/- S.D.) 92.9% +/- 12.8% of patients, compared with 80.1% +/- 15.5% of patients who received aPTT-based monitoring (p < 0.0001). After implementation of HCV-based monitoring, the rate of correct heparin dosage adjustments was improved (mean +/- S.D. 94.7% +/- 7.8% versus 89.3% +/- 14.0%, p = 0.01), and the time to attainment of the first target anticoagulation value was shorter (mean +/- S.D. 16.4 +/- 10.6 hours versus 21.5 +/- 14.8 hours, p = 0.03). Conclusion. The HCV, which relates measured aPTT values to corresponding antifactor Xa concentrations, was substituted for aPTT in heparin nomograms and appeared to be a viable alternative to the a PTT.