Increased factor XIa levels in patients with a first acute myocardial infarction: The introduction of a new thrombin generation based factor XIa assay

•This study is the first application of a new thrombin generation based FXIa assay•The FXIa assay enables the direct quantification of FXIa plasma levels•In AMI patients FXIa levels were significantly increased at 0 compared to 6 months•FXIa levels were significantly higher in AMI patients compared to healthy controls•The FXIa plasma concentration was not associated with the risk of recurrence

ObjectiveOne of the contributing mechanisms in acute myocardial infarction (AMI) is plasma hypercoagulability. Recently, it was suggested that factor XI activation might play a role in atherothrombosis. To quantify factor XIa plasma levels, we developed a new thrombin generation based assay and hypothesized that in AMI patients factor XIa levels are increased during the acute thrombotic event.MethodsA prospective cohort study was performed including 56 patients with first AMI. Blood was collected upon admission and after 6 months. Reference blood samples were obtained from 30 apparently healthy control subjects. Plasma samples were diluted (1:5) in factor XI deficient plasma and factor XIa plasma levels were established using a reference curve (0-12.5 pM factor XIa) and an inhibitory anti-factor XIa antibody. The established FXIa concentrations were related to the 1-year outcome.ResultsFactor XIa plasma concentrations were significantly increased in AMI patients on admission compared to 6 months after the event (3.7 pM [2.7-5.5] vs. 2.8 [1.9-4.3], median ± IQR; P = 0.001) and compared to healthy controls (3.7 pM [2.7-5.5] vs. 2.7 [1.6-4.2], median ± IQR; P = 0.004). However, a high factor FXIa level at baseline was not significantly associated with a recurrent cardiovascular event (OR 1.26, 95%CI 0.33-4.7).ConclusionsThis study presents the first application of a new thrombin generation based factor XIa assay, showing significantly increased factor XIa levels in AMI patients on admission compared to 6 months after the event and compared to healthy controls. The factor XIa concentration was not associated with the risk of recurrence.