Antiphospholipid antibodies impact the protein C (PC) pathway behavior.

Antiphospholipid antibodies may interfere with the PC pathway, displaying a resistance to the activated PC (resistant phenotype). This effect was evaluated by the APCR and the ProCG systems in 36 lupus anticoagulant samples, yielding abnormal results in 47% of APCR(original), 17% of APCR(modified), and 22% of ProCG test. ProCG values correlated with APCR(original) but not with APCR(modified). Most of lupus anticoagulants affecting the PC pathway showed abnormal APCR(original) results but not abnormal ProCG values. The different behavior between both systems may be due to the heterogeneity of the antibodies or could be attributed to the fact that, in the ProCG, a PC activator is added, while the APCR employs already activated exogenous PC.