Normal thromboelastography with a markedly prolonged activated partial thromboplastin time in severe prekallikrein deficiency: Implications for perioperative hemostatic assessment.

BACKGROUND: Prekallikrein (PK) deficiency is a rare contact factor deficiency that can markedly prolong the activated partial thromboplastin time (aPTT) without a bleeding phenotype. Because viscoelastic hemostatic assays also rely on contact activation, their behavior in severe PK deficiency is relevant to perioperative evaluation of isolated aPTT prolongation. We describe thromboelastography (TEG) 6s findings in a patient with severe PK deficiency.

STUDY DESIGN AND METHODS: A 59-year-old woman without a bleeding history was evaluated for an isolated prolonged aPTT identified during preoperative testing. Studies included prothrombin time (PT), thrombin time, an anti-factor Xa assay, aPTT mixing studies including with PK-deficient plasma, and factor VIII, IX, XI, and XII activities. PK antigen was assessed by western immunoblotting. Whole blood viscoelastic testing was performed on a TEG 6s analyzer.

RESULTS: The patient had a markedly prolonged aPTT (87.4 s, reference range [RR]: 24.5-34.0 s) with normal PT, thrombin time, and a negative anti-factor Xa assay. The aPTT corrected on mixing with normal pooled plasma but not with PK-deficient plasma. Factor VIII, IX, XI, and XII activities were normal or modestly elevated. Western immunoblotting showed absent PK antigen, establishing cross-reactive material-negative PK deficiency. Despite the prolonged aPTT, TEG 6s parameters were normal, including the citrated kaolin R time (4.6 min, RR: 4.6-9.1 min). The patient underwent surgery without hemostatic complications or transfusion.

DISCUSSION: Severe PK deficiency may markedly prolong the plasma-based aPTT without parallel abnormalities on TEG 6s, highlighting assay-specific differences in sensitivity to PK deficiency.