Different heparin lots: Does it matter?

OBJECTIVE: To assess the impact of heparin lot on the correlation between heparin concentration and activated partial thromboplastin time (aPTT), the aPTT therapeutic range, and the heparin level. DESIGN: Retrospective analysis of data from 2 previous studies. SETTING: Teaching institution with 929 beds. PATIENTS: Ninety-five patients receiving heparin with 5 different lots (study 1) and 35 patients receiving heparin with 3 different lots (study 2). MAIN OUTCOME MEASURES: Laboratory-based aPTT and heparin level by anti-factor Xa analysis. Standard heparin curves were created for each lot. Each patient's heparin level was determined off each standard curve. RESULTS: Correlations between heparin concentration and aPTT ranged from 0.87 to 0.89 (study 1) and 0.86 to 0.87 (study 2). Slopes of regression lines were not significantly different. Therapeutic ranges generated from lot-specific heparin levels were similar. Average bias in heparin levels from varying lots ranged from 0.005 to 0.036 units/mL. CONCLUSIONS: The recommendation to reevaluate the aPTT therapeutic range with each new lot of heparin requires further evaluation.

Use of the activated partial thromboplastin time for heparin monitoring.

The objectives of the present study were to evaluate the relationship between heparin concentration and activated partial thromboplastin time (aPTT) results, define a heparin concentration-derived therapeutic range for each aPTT instrument, compare aPTT- and heparin concentration-guided dosage adjustment decisions, and compare laboratory- and bedside aPTT-guided decisions. In phase 1, 102 blood samples were analyzed for bedside and laboratory aPTTs and heparin concentration (used to establish aPTT therapeutic range). In phase 2, 100 samples were analyzed in the same manner. Correlations for aPTT compared with heparin ranged from 0.36 to 0.82. Dosage adjustment decisions guided by the aPTT agreed with those based on heparin concentration 63% to 80% of the time. Laboratory and bedside aPTT dosage adjustment decisions agreed 59% to 68% of the time. The correlation of aPTT with heparin concentration and agreement between aPTT- and heparin-guided decisions vary with the aPTT instrument. Decisions guided by laboratory aPTT results often disagree with decisions guided by bedside aPTT results.

Correlation of activated clotting time and activated partial thromboplastin time to plasma heparin concentration.

STUDY OBJECTIVE: To determine the correlation between activated clotting time (ACT) or activated partial thromboplastin time (aPTT) and plasma heparin concentration. DESIGN: Two-phase prospective study. SETTING: University-affiliated community hospital. PATIENTS: Thirty patients receiving continuous-infusion intravenous heparin. INTERVENTIONS: Measurement of ACT, aPTT and plasma heparin concentrations. MEASUREMENTS AND MAIN RESULTS: Linear and log linear correlations were determined between clotting time tests and heparin concentrations. Linear correlations yielded r values of 0.58 for ACT (p=0.008) and 0.89 for aPTT (p=0.0001). Log linear correlations yielded r values of 0.60 for ACT (p=0.005) and 0.88 for aPTT (p=0.0001). A decision analysis was performed to determine possible consequences of dosage adjustments based on either test in relationship to the decision based on plasma heparin concentration. The decision analysis based on ACT disagreed with corresponding decisions based on plasma heparin concentration in 15 of 30 patients; 13 disagreements may have increased the risk of bleeding, and the other 2 may have increased the risk of thrombosis. Decisions based on aPTT disagreed with corresponding decisions based on plasma heparin concentration in 13 of 30 patients; 2 disagreements may have increased the risk of bleeding, and the other 11 may have increased the risk of thrombosis. CONCLUSION: There are significant statistical linear and log linear correlations between both clotting time tests and plasma heparin concentrations, with aPTT showing stronger correlation than ACT. However, decisions regarding heparin therapy based on ACT may increase a patient's risk of bleeding, whereas decisions based on aPTT may increase the risk of thrombus progression or rethrombosis.