Influence of In Vitro Acidification on APTT Measured With Two Different Reagents on Two Different Analyzers

We designed a study to evaluate whether in vitro–induced acidosis may influence APTT values using two different analyzers (with optical or mechanical clot detection) and two distinct reagents. The results of our study demonstrate that APTT values, measured with two distinct reagents on two different hemostasis analyzers, progressively increased as the sample pH was systematically reduced in vitro. This finding suggests that the prolonged APTT values might be at least partially attributable to an in vitro artifact rather than an in vivo metabolic effect influencing the coagulation pathway. Supporting this hypothesis is the observation that varying degrees of APTT prolongation depending on the specific reagent-analyzer combinations used. This indicates a potential reagent-specific sensitivity to pH changes, likely attributable to differences in clotting activators and phospholipid composition, which would otherwise suggest that measuring pH in samples with APTT prolongation before conducting additional, labor-intensive investigations may be a practical and efficient approach. Nevertheless, these findings underscore the need to consider pH as a critical preanalytical variable when interpreting APTT test results, as pH fluctuations may differentially affect assay outcomes depending on reagents and analyzers.