Comparative analysis on characteristics of two activated partial thromboplastin time reagents

Background For the lack of standardized activated partial thromboplastin time (APTT), it has been pointed out that there are differences in values among several reagents. Recently, we have performed a parallel measurement on two reagents, Thrombocheck APTT-SLA and Coagpia APTT-n, and resulted with some dissociated samples. The purpose of this study is to clarify the possible factors related to Delta APTT, the difference in measured values between the two reagents. Materials and Methods In order to clarify the factors related to Delta APTT, multiple regression analysis was performed on 8324 samples, using clinical laboratory data of all test items requested simultaneously with APTT. To confirm the items extracted from the multiple regression analysis, the target substance was spiked to pooled plasma and measured with two APTT reagents. Additionally, by spiking phospholipids, the effect on APTT measurement system was assessed. Result Multiple regression analysis detected albumin-globulin ratio (AGR), C-reactive protein (CRP), hematocrit, and prothrombin time as factors related to Delta APTT (p < 0.001). Results revealed no significant differences when albumin was added to change the AGR. Whereas with the addition of CRP, prolongation of APTT was observed in Coagpia APTT-n compared to Thrombocheck APTT-SLA (p < 0.001). This prolongation was canceled by the addition of phospholipids, suggesting the interaction of CRP with phospholipids leads to the pseudo-prolongation. Conclusion It is considered that the pseudo-prolongation of APTT is triggered by the interaction of CRP on the phospholipid in Coagpia APTT-n, which contributed to the APTT dissociation.