Unexplained Prolonged PTT

From Dr. Samir Patel: George, I have enjoyed reading the blog for many years now (since fellowship) and am wondering if you could shed some light on a patient I am working up. This is a 90 year old woman who was sent for evaluation after she developed a hematoma post cardiac catheterization (no need for transfusion, bleeding controlled with pressure). At that time she was noted to have a prolonged partial thromboplastin time (APTT, PTT) and so came for evaluation. I have done almost everything I can think of and still can not explain what is causing her prolonged PTT, and more importantly she is in need of repeat cardiac cath and likely valve repair surgery in the future. She is not on any medications that could be causing this for many months. Mixing studies suggest the presence of an inhibitor.

Below is everything that has been tested (some of them have been done up to 3 times at different labs with similar results):

• PTT 39.5s (26.4-37.7s)
• PT 11.5s (nl)
• Thrombin time 19.8s (nl)
• F V 67% (68%-136%)
• F VIII 94% (nl)
• F IX 103% (nl)
• F X 82% (nl)
• F XI 76% (78-157%)
• F XII 66% (nl)
• LA screen negative (nl)
• Prekallikrein 77% (nl)
• HMWK 70% (nl)
  Mixing studies:
• PTT patient 36.6s
• PTT of PNP 33.6s
• PTT of 1:1 mix 34.5s
• patient incubated 42.9s
• PNP incubated 34.7s
• 1:1 mix incubated 40.1s

Thanks for any help you can provide, Samir.

Hello, Dr. Patel, and thank you for this interesting case, which highlights the problems associated with laboratory analysis of a slightly, though consistently prolonged PTT. You have appropriately investigated all the potential causes for your patient’s prolonged PTT, ruling out a coagulopathy. The incubated mix could indicate a specific inhibitor such as auto-anti factor VIII, however the normal factor VIII activity appears to contradict this conclusion. You may wish to follow up with a Bethesda titer, though as a general rule, the Bethesda titer is only performed when the factor VIII level is deficient.

As a preliminary look from a lab scientist’s non-clinical viewpoint may I suggest that the patient’s prolonged PTT may be a borderline finding and may suggest no coagulopathy. This is supported by the results of the second PTT performed as part of the mixing study, which appears to be within the reference interval.

Other potential causes for your patient’s hematoma, independent of her PTT, include bleeding from the surgical site, a localized anatomical abnormality, diminished vascular integrity, thrombocytopenia, an acquired platelet function disorder, or factor XIII deficiency, listed in the order of decreasing prevalence. I’ve invited wo physician colleagues to further comment on the case, meanwhile, thank you for your question.