MCQ Hematology Answer 14

Answer: C

In this case where there have been several past cardiac surgical procedures, the chances are high that the patient was exposed to “fibrin glue” which contains bovine thrombin (and bovine factor V in this semi-purified preparation). Inhibitors to bovine thrombin and factor V commonly develop, and although the antibody to bovine thrombin usually does not cross react with human thrombin, the antibody to factor V frequently cross reacts with human factor V and can cause serious bleeding. A factor V test showing a decreased level should be followed by a factor V inhibitor assay to confirm this; a thrombin time performed with human thrombin as the reagent would be normal. DIC is not likely in the presence of a normal platelet count and this degree of abnormality in the coagulation tests. A hereditary dysfibrinogenemia could cause prolonged assays in all 3 tests noted above, but it is not likely to cause bleeding, and it was not detected on the previous testing. A lupus anticoagulant would not cause a prolonged thrombin time. Heparin would not be expected to cause this prolongation of the prothrombin time, and thrombin time would be greater than 2 minutes if the aPTT is increased to 51 seconds by heparin.

References:

1. Zehnder JL, Leung LLK. Development of antibodies to thrombin and factor V with recurrent bleeding in a patient exposed to topical bovine thrombin. Blood 1990; 76:2011-16.

2. Ortel TL, Charles LA, Keller FG, Marcom PK, Oldham HN, Kane WH, Macik BG. Topical thrombin and acquired coagulation factor inhibitors. Amer J Hemat 1994; 45:128-35.

Category: Hematology MCQs