Comparing different lots of activated partial thromboplastin time reagent: analysis of two methods

Area of Science:

• Clinical Chemistry
• Hematology
• Laboratory Medicine

Background:

• Activated partial thromboplastin time (APTT) is crucial for monitoring unfractionated heparin (UH) therapy.
• Variability in APTT reagent performance can affect therapeutic decisions.
• Assessing lot-to-lot consistency is essential for reliable laboratory diagnostics.

Purpose of the Study:

• To compare the performance of two different lots of APTT reagent from the same manufacturer.
• To evaluate the impact of reagent lot variability on APTT results and therapeutic ranges for UH.
• To assess the agreement between different APTT reagent lots and within-lot duplicates.

Main Methods:

• Analysis of 200 plasma samples using two APTT reagent lots on the same instrument.
• Comparison with 267 additional plasma samples analyzed in duplicate with a single reagent lot.
• Application of regression analysis and Bland-Altman assessment of agreement on logarithmically transformed data.

Main Results:

• Suboptimal agreement was observed with regression analysis, particularly at higher APTT values.
• The new reagent lot yielded results that were 88.9% of the old lot's values, narrowing the UH therapeutic range.
• Duplicate APTT determinations were 97.6% of the initial value, with 95% limits of agreement of +/-10% within the therapeutic range.

Conclusions:

• Significant variability exists between APTT reagent lots, impacting the therapeutic range for unfractionated heparin.
• The Bland-Altman method is superior to regression analysis for assessing agreement between APTT reagent lots.
• APTT variability, both within and between lots, may limit its optimization for monitoring UH therapy.