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

Abstract

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 aPTT.

Performance of Anti-Factor Xa Versus Activated Partial Thromboplastin Time for Heparin Monitoring Using Multiple Nomograms

“…To our knowledge, this is the second largest of only 4 previous studies which directly compared aPTT and anti-Xa nomograms for monitoring UFH. 8 –10,12 Rosborough evaluated 268 patients who received a single treatment protocol based on deep vein thrombosis (DVT) treatment and showed that despite a modest increase in cost, patients in the anti-Xa group required fewer monitoring tests and dose changes compared to the aPTT. 8 Fruge and Lee studied 141 patients who received a single protocol for all indications, although dosing differed slightly between the aPTT and anti-Xa nomograms.…”

Antifactor Xa Levels versus Activated Partial Thromboplastin Time for Monitoring Unfractionated Heparin

“…A therapeutic aPTT range is determined by plotting on a graph simultaneous aPTT and antifactor Xa values from patients receiving heparin, and from the lines of best fit, finding the aPTT values that correspond to 0.3 and 0.7 unit/ml, respectively. With the large degree of variability already known, and the enhanced availability of antifactor Xa automation, some investigators sought to explore if the use of antifactor Xa levels directly for patient care was more feasible than their use in establishing institution‐specific aPTT goal ranges (Table ) …”

“…A prospective, observational, cohort study evaluated the use of a heparin correlation value, in which the antifactor Xa concentrations were correlated with the aPTT, then the measured aPTT was correlated back to antifactor Xa levels; use of this value may help to account for disadvantages of both monitoring methods. Only the aPTT (and not the antifactor Xa level) is measured with this method, but the result is recalculated as a heparin correlation value.…”

“…With the large degree of variability already known, and the enhanced availability of antifactor Xa automation, some investigators sought to explore if the use of antifactor Xa levels directly for patient care was more feasible than their use in establishing institution-specific aPTT goal ranges ( Table 2). [44][45][46][47][48][49] A key study leading to the ACCP and CAP recommendations was published in 1994. 44 The investigators randomized consecutive patients with acute venous thromboembolism that required treatment with high doses of UFH in the preceding 24 hours to be subsequently managed by either antifactor Xa levels or by the aPTT.…”

“…Another study reported a similar rate (89%) of therapeutic levels within 24 hours, using a weight-based heparin protocol based on an aPTT goal of 46-70 seconds, which correlated with an antifactor Xa range of 0.38-0.57 unit/ml. 40 A prospective, observational, cohort study evaluated the use of a heparin correlation value, in which the antifactor Xa concentrations were correlated with the aPTT, then the measured aPTT was correlated back to antifactor Xa levels 48 ; use of this value may help to account for disadvantages of both monitoring methods. Only the aPTT (and not the antifactor Xa level) is measured with this method, but the result is recalculated as a heparin correlation value.…”