Marked discrepancy between coagulometric Protein C activity assays with the pro‐thrombotic Protein C Asn2Ile substitution

Abstract

We demonstrate that coagulometric assays are not equally sensitive to clinically important functional defects of PC and that multiple assays may be required to identify all variants.

Guidelines on the laboratory aspects of assays used in haemostasis and thrombosis

“…APTT‐based assays are not influenced by the type of contact activator, but the phospholipid composition is important, as it influences sensitivity to the anticoagulant effect of APC, which in turn is related to the reagent sensitivity to FV and FVIII. There is also variability according to the protein S (PS) dependence of the assay . Different graphical transforms are required, depending on the APTT reagent, to achieve a linear dose–response curve .…”

Laboratory testing issues for protein C, protein S, and antithrombin

“…The clotting‐based assays utilize mainly the PTT, but assays using the PT or RVVT have been developed. The PTT‐based assays are not influenced by the PTT activator, but are or can be by the phospholipid source and concentration (rare defects) . In addition, increased levels of factor VIII and factor V Leiden underestimate, and increased levels of PS can overestimate the PC value in plasma .…”

“…The PTT‐based assays are not influenced by the PTT activator, but are or can be by the phospholipid source and concentration (rare defects) . In addition, increased levels of factor VIII and factor V Leiden underestimate, and increased levels of PS can overestimate the PC value in plasma . These influences can be eliminated by dilution of the plasma with PC‐deficient plasma; however, this modification reduces the lower limit of PC detection and increases assay cost .…”

Sources and solutions for spurious test results in coagulation

“…Also, rarely within the analytical phase, the unique molecular defects described above, in which the in vitro results do not reflect the in vivo process, should be considered, and this is accomplished by knowing the assay structural and component limitations that might bring about an unexpected result when an abnormal molecule exists …”