Question

After demonstrating that heparin was not the cause of an elevated PTT, a patient’s plasma was mixed 1:1 with normal plasma, and a PTT was performed on the mixture. The resulting PTT was in 10% of the normal plasma. What was the most likely cause of these results?

On a different patient’s sample, after demonstrating that heparin was not the cause of an elevated PTT, the patient’s plasma was mixed 1:1 with normal plasma and a PTT was performed. The PTT remained elevated. What was the most likely cause of these results?

Subject is HEMATOLOGY

Answer 1

1) Mixing study is done to distinguish between coaggulation factor deficiency like factor VIII deficiency and factor inhibitor (Lupus anticoagullant).

2) This test is perfoemed if the patient has prolonged coaggulation assay result for PTT test. Partial thromboplastin time (PTT) test determines the time taken for the blood clot formation. Low levels of clotting factors can cause excessive bleeding.

3) The negative result of PTT can be due to medication like heparin, warfarin, antihistamines, aspirin, vitamin C, chlorpromazine.

4) However, since it was demonstrated that heparin is not the cause of elevated PTT result, mixing study was performed.

5) In mixing study equal volumes of patient plasma and normal plasma are mixed to repeat PTT on the mixture. The basic principle is that the normal plasma contributes a sufficient concentration of clotting factors to "correct" for a factor deficiency.

6) In case of first condition wherein PTT result was in 10% of normal plasma, the result indicates it is characteristic of factor deficiency.

7) On a different patient sample when mixing study performed gave an elevated PTT result, that means mixing study does not correct the PTT indicates a factor inhibitor.

8) To negate the false negative test for factor inhibitor, one may prolong the sample incubation after mixing for 1-2 hr at 37 degree C. Specimens with time-dependent inhibitors will not correct the incubated mix.

9) The incubated mixing study is necessary for diagnosing coagulation factor inhibitor.

10) Spontaneous inhibitors to coagulation factors are autoantibodies that usually appear in the elderly, but may also occur in patients with immunological disorders such as lupus, lymphoma, asthma or drug reactions