CASE SERIES SUMMARY: Factor XII (FXII) deficiency is a rare autosomal recessive genetic disorder in cats, leading to singular prolonged activated partial thromboplastin clotting time (aPTT) without increased bleeding risk. This case series describes two cats diagnosed with FXII deficiency using the ClotPro system, a point-of-care viscoelastic coagulation test. Both cats exhibited significantly prolonged aPTT and intrinsic pathway clotting time but maintained normal clot strength, as indicated by thromboelastography (TEG). FXII deficiency was confirmed through quantitative ELISA measurement. Despite prolonged clotting times, the cats did not demonstrate clinical bleeding, suggesting that FXII deficiency does not increase bleeding risk. However, larger controlled studies are necessary to further investigate the utility of TEG in cats with FXII deficiency or other coagulation disorders.

RELEVANCE AND NOVEL INFORMATION: This study addresses the diagnostic challenges associated with FXII deficiency, a condition that can lead to misinterpretation of coagulation results and unnecessary treatments. It highlights the application of the ClotPro system in feline medicine, providing deeper insights into coagulation dynamics and confirming that FXII deficiency does not inherently increase bleeding risk despite prolonged clotting times.