The analysis of false prolongation of the activated partial thromboplastin time (activator: silica): Interference of C‐reactive protein

Abstract

C-reactive protein interferes with the detection of APTT, especially in STA-R Evolution (activator: silica) system. The increasing in C-reactive protein results in a false prolongation of the APTT (activator: silica), and it is most likely that C-reactive protein interferes the coagulable factor binding of phospholipid.

Comparative analysis on characteristics of two activated partial thromboplastin time reagents

“…However, it has been reported that for some APTT reagents, CRP can be a direct cause of a pseudo‐prolongation of APTT. 9 On the other hand, although the AGR showed a negative correlation with ΔAPTT in multiple regression analysis, no significant change was observed even when AGR was changed by ALB addition. This suggests that the AGR does not directly affect the APTT reaction system.…”

“…Previous studies have reported that CRP inhibits phospholipids in some APTT reagents and causes a pseudo‐prolongation of APTT. 9 Therefore, in order to investigate whether CRP inhibits phospholipids in the reagent, purified CRP was added to phospholipid added samples and the effects on APTT values were examined. As shown in Figure 3 , sample with plasma and CRP showed a significant prolongation of APTT‐n as compared with to samples without the addition of CRP nor phospholipids.…”

“…Finally, previous studies have reported that CRP binds to some phospholipids. 9 , 17 Furthermore, since the phospholipids composed in APTT‐SLA and APTT‐n vary; synthetic phospholipids, and phospholipids derived from a rabbit brain, we have focused on phospholipids, and addition of phospholipids was examined. Results showed that the prolongation caused by CRP was canceled by the addition of phospholipid, and it was presumed that the binding of CRP to the phospholipid in the APTT‐n reagent triggered the prolongation of APTT.…”

“…Finally, previous studies have reported that CRP binds to some phospholipids 9,17 . Furthermore, since the phospholipids composed in APTT‐SLA and APTT‐n vary; synthetic phospholipids, and phospholipids derived from a rabbit brain, we have focused on phospholipids, and addition of phospholipids was examined.…”

Heparin – Messias or Verschlimmbesserung?

“…Conversely, use of anti‐Xa monitoring in addition to APTT may be beneficial in COVID‐19 patients in whom heparin resistance is suspected. APTT readings may be falsely shortened in patients receiving UFH with an elevated C‐reactive protein, dependent upon the chosen assay or high FVIII levels 49 . Anti‐Xa monitoring may therefore be preferable in these patients, which is of relevance to a significant proportion of COVID‐19 patients 50 .…”