Evaluation of thromboelastography in two factor XII-deficient cats

CASE SUMMARY: The current report describes thromboelastography (TEG) findings in two cats with factor XII (FXII) deficiency. The first cat was diagnosed with bilateral perinephric pseudocysts; hemostatic testing was performed prior to performing renal aspirates. The second cat was healthy; hemostatic testing was performed prior to inclusion into a research project. Both cats had markedly prolonged partial thromboplastin times and hypocoagulable TEG tracings when samples were activated with kaolin. However, when tissue factor (TF) was used to activate the sample, both cats had normal-to-hypercoagulable TEG tracings. The cats each had a subnormal FXII level. RELEVANCE AND NOVEL INFORMATION: TEG is becoming widely used to investigate hemostasis in veterinary patients, and TEG results in cats with FXII deficiency have not been previously reported. FXII deficiency is the most common hereditary hemostatic defect in cats. While FXII deficiency does not lead to in vivo hemorrhagic tendencies, it can lead to marked prolongation in activated partial thromboplastin and activated clotting times, and cannot be differentiated from true hemorrhagic diatheses without measuring individual factor activity. With the increased use of TEG to evaluate hemostasis in veterinary patients, it is important to recognize the effects of FXII deficiency on this testing modality. The finding of a hypocoagulable kaolin-activated TEG tracing and a concurrent normal TF-activated TEG tracing in samples should prompt clinicians to consider ruling out FXII deficiency.