Circulating fibroblast activation protein activity and antigen levels correlate strongly when measured in liver disease and coronary heart disease

Background and aimCirculating fibroblast activation protein (cFAP) is a constitutively active enzyme expressed by activated fibroblasts that has both dipeptidyl peptidase and endopeptidase activities. We aimed to assess the correlation between cFAP activity and antigen levels and to compare variations in levels.MethodsIn plasma of 465 control individuals, 368 patients with coronary heart disease (CHD) and 102 hepatitis C virus (HCV) infected patients with severe liver disease before and after liver transplant, cFAP activity levels were measured with a newly developed cFAP activity assay. In the same samples, cFAP antigen levels were measured using a commercially available cFAP ELISA. Correlation analyses between activity and antigen levels were performed by calculating Pearson’s correlation coefficient (ρ). Additionally, normal ranges, determinants and differences between cohorts and between anticoagulants were investigated.ResultscFAP activity and antigen levels significantly correlated in controls (ρ: 0.660, pConclusionsFor analyzing cFAP levels, either activity levels or antigen levels can be measured to investigate differences between individuals. However, it is of importance that blood samples are collected in the same anticoagulant.