Acquired hemophilia A (AHA)2 is a rare but life-threatening bleeding disorder caused by an autoantibody directed against factor VIII, known as a factor VIII–specific inhibitor. Approximately 50% of AHA cases are idiopathic, whereas the remaining cases are often associated with an autoimmune disorder, malignancy, pregnancy, or drugs. The diagnosis must be made promptly to minimize the time that patients are at risk of severe bleeding and to avoid nonessential invasive procedures and delay in the initiation of appropriate treatment.
In this Clinical Case Study by Ehrenschwender et al., the authors described the step-by-step laboratory investigations of the isolated prolongation of the activated partial thromboplastin time (aPTT) in an elderly individual with unprovoked bleeding. This case stresses the importance of automatic laboratory investigation of isolated aPTT prolongation in identifying and treating patients with AHA. Prompt and thorough laboratory investigation is essential, considering that up to 6% of patients with AHA have been reported to have no bleeding at presentation.
One aspect not discussed in the Clinical Case Study is that AHA may occur in patients with lupus anticoagulant (LAC), with or without thrombosis. These patients often are receiving anticoagulation therapy. Because LAC also causes aPTT prolongation, it is important not to simply attribute aPTT prolongation to LAC or therapy and then stop further laboratory workup, especially if patients have bleeding episodes. Furthermore, given that LAC interferes with in vitro clotting-based assays, esoteric chromogenic assays should be used in this setting to measure factor VIII activity and the strength of the factor VIII inhibitor, which can provide essential guidance regarding patient management.
Also of note is that although coagulation factor assays are designed to quantify factor activity levels, the assays can also detect interfering inhibitors, including LAC and inhibitors of individual factors (in which “nonparallelism” indicates the presence of an inhibitor), and therefore are an integral part of laboratory investigations of isolated aPTT prolongation, as was demonstrated in this case.
↵2 Nonstandard abbreviations:
- acquired hemophilia A;
- lupus anticoagulant.
Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 3 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; and (c) final approval of the published article.
Authors' Disclosures or Potential Conflicts of Interest: No authors declared any potential conflicts of interest.
- Received for publication March 7, 2012.
- Accepted for publication March 9, 2012.
- © 2012 The American Association for Clinical Chemistry