EXPRESS: Point-of-care ClotPro thromboelastography in three Maine Coon cats with factor XI deficiency

Case series summary Factor XI (FXI) deficiency is a hereditary autosomal recessive coagulation disorder recently identified in Maine Coon cats. Affected cats typically show markedly prolonged activated partial thromboplastin time (aPTT), yet the bleeding risk remains unclear. This case series describes three Maine Coon cats homozygous for the F11 variant linked to FXI deficiency and wild type for both known F12 variants. Factor XI activity ranged from 15-58% (RI 69-134). All three cats exhibited prolonged aPTT, with prolonged intrinsic pathway clotting times in the two cats in which the IN-test could be performed, while clot firmness was preserved in all three. Increased FIB-test maximum lysis in two cats was of uncertain significance given the use of human reference intervals. Invasive procedures comprised fine-needle aspiration, gastroduodenoscopy with biopsy collection, abdominocentesis and elective ovariohysterectomy, and were performed without haemorrhage, consistent with the variable penetrance of the bleeding tendency reported with this variant rather than evidence that FXI deficiency confers no bleeding risk. Relevance and novel information This report describes the viscoelastic profile of FXI-deficient cats, in which the intrinsic pathway defect was reflected in markedly prolonged IN-test clotting times with preserved clot firmness. Whether viscoelastic testing can discriminate bleeding risk will require evaluation of affected cats with a documented bleeding phenotype, and feline-specific ClotPro reference intervals will be essential. This study demonstrates the clinical utility of screening Maine Coon cats for hereditary factor XI deficiency to aid the interpretation of prolonged clotting times in the aPTT and in viscoelastic screening tests.