Prolonged partial thromboplastin time: To mix or not to mix - is that the question?

Reflex factor coagulation testing in patients with an unexplained prolonged aPTT: An institutional retrospective review

BACKGROUND

We aim to determine the clinical utility of reflex coagulation investigations (RCI) for prolonged lupus insensitive activated partial thromboplastin time (aPTT) at our institution.

METHODS

We retrospectively reviewed all potential RCI (lupus insensitive aPTT of ≥32s) from April 2014 to June 2019. Our diagnostic algorithm requires completion of RCI only if samples had no interfering medications to explain a prolonged aPTT and were either from a preoperative sample or from a patient presenting with unexplained bleeding. Appropriate RCI samples undergo further investigations with one-stage factor activity testing for factors 8(FVIII), 9(FIX), and 11(FXI) reflexively. Data were obtained through electronic medical records to capture clinical characteristics, laboratory findings, prophylactic hemostatic replacement, and bleeding outcomes.

RESULTS

Three thousand and three hundreds seventeen samples from 2940 distinct patients were considered as potential RCI during the study period. 263/3317 (8%) samples had RCI completed. Of those, 55/263 (21%) had abnormal factor testing, with the majority from preoperative setting (43/55; 78%). 5/43 (12%) patients were referred to hematology for preoperative evaluation. 5/43 patients received preoperative hemostatic support. A total of 5 patients (5/43) developed postop bleeding. Six patients (6/55) had RCI for unexplained bleeding, and five patients (83%) had a newly identified clinically significant bleeding disorder.

CONCLUSION

Reflex coagulation investigations benefited patients presenting with unexplained bleeding as this expedited the diagnosis and management of clinically significant bleeding disorders. RCI for preoperative evaluation infrequently led to additional hemostatic support/referral to hematology. The lack of additional workup for an abnormal factor activity level suggests laboratory alert fatigue as a potential contributory factor.

Acquired Hemophilia A

Acquired hemophilia A is a potentially severe bleeding disorder caused by antibodies against the patient's own factor VIII. Acquired hemophilia A is rare. It is most commonly diagnosed in older individuals; about one-half of cases of acquired hemophilia are associated with underlying conditions, including autoimmune disease, cancer, and pregnancy. The diagnosis of acquired hemophilia A can be suspect with an isolated activated partial thromboplastin time elevation, and confirmed with demonstration of reduced factor VIII activity and the presence of a specific factor VIII inhibitor. Treatment of acquired hemophilia A involves control of bleeding, and eradication of the inhibitor.