Limited value of testing for factor XIII and α2‐antiplasmin deficiency in patients with a bleeding disorder of unknown cause

Introduction In patients with an increased bleeding tendency, extensive diagnostic blood testing is often performed. When results of tier 1 assays of primary haemostasis are normal, protocols recommend additional testing to rule out rare disorders including coagulation factor XIII (FXIII) and α2‐antiplasmin (α2AP) deficiency. Aim To evaluate the added diagnostic value of FXIII and α2AP levels in patients with a bleeding disorder of unknown cause (BDUC). Methods A retrospective monocentre cohort study between August 2011 and August 2023 was conducted. In all patients with bleeding tendencies and normal diagnostic tests for von Willebrand disease and platelet function, FXIII and α2AP were measured. Results We included 158 consecutive patients; mean ISTH‐BAT scores were 8.2 (SD ± 3.7) in children, 6.2 (SD ± 2.1) in men and 10.6 (SD ± 3.3) in women. Median age was 37 (range 5–79) years, 88.6% of patients were female. Patients displayed median FXIII activity of 111% (IQR = 97–131) and median α2AP activity of 112% (IQR = 103–119). Three (1.9%) patients had FXIII levels