Interference in specialized coagulation assays affecting the protein C pathway: Effects of marked haemolysis, hyperbilirubinaemia and lipaemia on chromogenic and clotting tests on two coagulation platforms.

Haemolysis, lipaemia and hyperbilirubinaemia represent important challenges in the coagulation laboratory. Test results are influenced not only by the degree of the interfering substance but also by the detection system.We investigated the interference of free haemoglobin, triglycerides and bilirubin on a "modified activated protein C (APC) resistance test," protein C activity and protein S (antigen and activity) with two coagulation analysers, the STA-R Evolution and the ACL TOP.Haemolysis interfered with all assays on the STA-R Evolution resulting in higher levels of protein C activity and lower levels of protein S and a decreased APC ratio compared with baseline levels. On the ACL TOP, haemolysis only diminished protein S antigen levels and the APC ratio. Lipaemia increased protein C activity and protein S activity levels on the STA-R Evolution, whereas APC-R decreased on the ACL TOP and protein S antigen could not be measured in any lipaemic samples. Hyperbilirubinaemia caused an increase in protein C activity and in protein S antigen and a decrease in APC-R on the STA-R Evolution, whereas a decline of protein C activity, of protein S antigen and of the APC-R could be observed in icteric samples on the ACL TOP.Our data show that the degree of interference associated with haemolysis, lipaemia and hyperbilirubinaemia is different in several assays. Some assay limitations were not reproduced, and limitations stated in kit inserts cannot be assumed to apply to all analysers.