Usefulness of Cumulative Summation of Differences Method for Determining APTT Reagent Suitability

Abstract

OBJECTIVE: The Cumulative Summation of Differences (CUSUM) is a recommended method for determining the consistency of one lot of Activated Partial Thromboplastin Time (APTT) reagent to another. This study investigates the usefulness of the CUSUM as a primary method for determining reagent suitability for APTT testing.

METHOD: Results for lot comparison, reference range and Ex-Vivo heparin sensitivity studies were obtained using the Beckman Coulter ACL TOP™ coagulation analyzer. APTT testing was performed using HemosIL™ SynthASiL w/CaCl and Heparin Xa testing was performed using the HemosIL™ Liquid Heparin Assay. Samples from normal patients and from patients taking heparin were tested.

RESULTS: The CUSUM calculation showed a difference in APTT reagent lot means that is within the acceptable range for this method, suggesting that the reagents were comparable. Reference range and heparin sensitivity studies demonstrated a clinically significant difference between the two reagent lot numbers tested.

CONCLUSION: The CUSUM method of evaluating reagent lot variation of APTT reagents should be used with caution as it may not completely reflect the performance of the reagent. Clinically significant differences between reagent sensitivity may not be detected. The results of reference range and heparin sensitivity studies should also be considered when determining the suitability of APTT reagents. In addition, due to research evidence that using the APTT test for monitoring patient anticoagulation therapy is problematic, an evaluation of the benefits of using other study methods and multiple study methods is suggested as well as continued examination of the use of the APTT as the test of choice for UF heparin monitoring.

ABBREVIATIONS: CUSUM - Cumulative Summation of Differences Method, APTT - Activated Partial Thromboplastin Time, UF - Unfractionated heparin, CAP - The College of American Pathologists, LIS - Laboratory information system, VRI - Verification of the reference interval, CLSI - Clinical and Laboratory Standards Institute