Testing for Passovoy defect in children with prolonged activated partial thromboplastin time (APTT).

Purpose: To investigate the value of testing for Passovoy defect using the commercially available Passovoy trait plasma (PTP) in children with prolonged activated partial thromboplastin time (APTT).

Patients And Methods: We studied 13 children with prolonged APTT that corrected in a 1:1 mix with normal human plasma but not with PTP. In most children, a thorough laboratory investigation of the intrinsic pathway factors and von Willebrand factor was performed.

Results: Five patients had bleeding manifestations and eight were asymptomatic. Measurement of von Willebrand factor and intrinsic pathway factors revealed abnormal values in eight patients (low von Willebrand activity in six patients, low factor XII in one patient, and the presence of lupus anticoagulant in one patient).

Conclusion: Our data suggest inability to diagnose Passovoy defect based on a mixing study. This study also raises the question of whether Passovoy defect exists as a distinct coagulation disorder.