Rare Prekallikrein Deficiency Identified During Workup of Isolated Prolonged Activated Partial Thromboplastin Time.

Prolongation of the activated partial thromboplastin time (aPTT) may signify an intrinsic factor deficiency or the presence of an inhibitor of coagulation, potentially placing a patient at increased risk for bleeding. However, a contact factor (ie, factor XII, prekallikrein, and high molecular weight kininogen) deficiency, which may also cause a prolonged aPTT, is not associated with clinical bleeding. A 71-year-old female had an isolated prolonged aPTT discovered during preoperative laboratory testing. Results of the initial coagulation tests demonstrated no deficiency of factors VIII, IX, or XI and no evidence for lupus anticoagulant or antiphospholipid antibodies. However, a mixing study test was suggestive of factor deficiency. Based on these results, contact factor activity tests were performed to identify any contact factor deficiency. The patient was determined to have a prekallikrein deficiency. Rare causes of isolated prolonged aPTT include contact factor deficiencies such as prekallikrein deficiency. Identification of a contact factor deficiency is clinically useful information, as it allows for a definitive assessment of bleeding risk. This case reports a rare factor deficiency and illustrates a contemporary approach to the workup of an isolated prolonged aPTT.