Role of cross-mixing tests in differentiating etiologies of prolonged aPTT: a single-center retrospective study

We reviewed 70 patients with prolonged activated partial thromboplastin time (aPTT) who underwent cross‑mixing tests (CMT) at our hospital. Median age was 70 years, median aPTT was 65.8 s, and 41 (58.5%) underwent CMT for preoperative screening. Visual CMT showed 13 deficiency‑pattern, 4 inhibitor‑pattern, and 53 lupus anticoagulant (LAC)‑pattern cases. Direct oral anticoagulants (DOACs) explained one deficiency‑pattern and two LAC‑pattern cases. All inhibitor‑pattern patients presented with bleeding and were diagnosed with acquired hemophilia A (AHA). Based on additional tests, including dilute Russell's viper venom time, LAC was considered the cause of aPTT prolongation in 59 cases (84.3%). No congenital hemophilia was identified. In CMT, an increase in aPTT after incubation in 50% mixed plasma clearly differentiated AHA (> 30 s) from LAC (< 25 s). All preoperative cases were ultimately attributed to LAC or DOACs; 37 patients proceeded to surgery without abnormal bleeding. These findings suggest that most preoperative aPTT prolongations seen in community practice are due to LAC, whereas AHA is rare. CMT provides same‑day results and is useful for rapidly excluding AHA in preoperative evaluation.