Background: Fibroblast activation protein (FAP) is a transmembrane glycoprotein with dipeptidyl-peptidase and endopeptidase activities and circulates in blood in a truncated, soluble form (sFAP). Fibrinolysis inhibitor alpha 2-antiplasmin (alpha 2AP) has been described as a potential in vivo substrate of sFAP. We aimed to investigate sFAP levels and alpha 2AP cleavage in young arterial thrombosis patients and in control individuals, study the correlation between sFAP levels and alpha 2AP cleavage and investigate determinants of these variables. Methods: sFAP levels and alpha 2AP cleavage were determined by ELISA in the plasma samples of 391 coronary heart disease (CHD) patients, 221 ischemic stroke patients, 51 peripheral arterial disease patients and 501 control individuals. Results: Median sFAP levels were similar in arterial thrombotic patients and in control individuals, but in CHD patients sFAP levels significantly increased with time (number of months) between the event and study inclusion (Spearman's rho: 0.209, p < 0.001), indicating reduced sFAP levels at time of event. sFAP levels and percentage a2AP cleavage significantly correlated in controls and in patients. Furthermore, sex, use of oral contraceptives and hyperlipidemia were significant determinants of sFAP levels. Conclusions: sFAP levelswere reduced in the CHD patient population, but only in the first months after the event, indicating that over time sFAP levels may normalize. The significant correlation between sFAP level and alpha 2AP cleavage indicates that in vivo sFAP (at least partly) regulates cleavage of alpha 2AP, irrespective of disease status. Differences in sFAP level due to sex, use of oral contraceptives and hyperlipidemia might suggest hormonal control of sFAP levels. (C) 2014 Elsevier Ireland Ltd. All rights reserved.