Factor XII deficiency (Hageman factor) is the most frequently detected hereditary coagulation abnormality in the cat. Factor XII participates in the contact pathway in laboratory testing, but is not essential for in vivo haemostasis: deficient cats have no bleeding tendency. Its relevance is mainly laboratory-related, because it markedly prolongs the aPTT and can confuse the interpretation of blood tests.

It is considered the most common hereditary coagulopathy of the cat and has been detected both in breeds and in domestic populations, with relevant prevalences in some studies. The specific figures vary widely depending on the population analysed: limited data.

- No haemorrhagic signs: it is a laboratory finding\n- Markedly prolonged aPTT with normal prothrombin time (PT)\n- Excessive bleeding only if another haemostatic defect coexists

The deficiency was described in humans in the mid-20th century through the study of Hageman factor and was later documented in the cat, where laboratories detected markedly prolonged aPTT in healthy animals. Family studies demonstrated autosomal recessive inheritance and a notable prevalence in feline populations. In 2015, Bender and colleagues characterised the feline F12 gene and the first causal mutation; in 2017 and 2019, Maruyama and colleagues described a second variant and two high-frequency mutations in domestic cats and cats of many breeds. Today it is included in genetic panels to correctly interpret coagulation tests and avoid overdiagnosis or unnecessary cancellations of procedures.

- It does not require treatment or exclusion from breeding for haemorrhagic reasons.\n- The test is useful for interpreting prolonged aPTT and avoiding unnecessary cancellation of biopsies or surgeries.\n- Record the result in the medical history so that anaesthesia and surgery are not delayed by an isolated aPTT.\n- Communicate the result to the laboratory: with a markedly prolonged aPTT in a healthy cat, measure factor activity.

An isolated prolonged aPTT with normal PT in an asymptomatic cat suggests factor XII deficiency; confirm with factor activity. Do not confuse it with rodenticide anticoagulant poisoning, which also prolongs the PT. A possible prothrombotic role of the deficiency has been discussed, with no clear clinical relevance. Plasma transfusion is not indicated to correct an asymptomatic aPTT.

1. Bender DE et al. 2015, Molecular characterization of cat factor XII gene and identification of a mutation causing factor XII deficiency in a domestic shorthair cat colony. Vet Pathol 52(2):312-20. PMID: 24793828. 2. Kier AB et al. 1980, The inheritance pattern of factor XII (Hageman) deficiency in domestic cats. Can J Comp Med 44(3):309-14. PMID: 7427778. 3. Maruyama H et al. 2017, A novel missense mutation in the factor XII gene in a litter of cats with factor XII deficiency. J Vet Med Sci 79(5):822-826. PMID: 28392508. 4. Maruyama H et al. 2019, Factor XII deficiency is common in domestic cats and associated with two high frequency F12 mutations. Gene 706:6-12. PMID: 31022435. OMIA:000364-9685.