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Prolonged PT and PTT That Don’t Correct


I am trying to work on a hemostasis project for school and I do not have any experience at all in a hemostasis laboratory apart from running PT and PTTs. What if a patient has an abnormal PT and PTT that are not corrected by mixing study? My guess is because it didn’t correct, it would be an inhibitor. What are possible causes for these results? Carrie

Hi, Carrie,

You are absolutely correct; the combination of a prolonged prothrombin time (PT) and partial thromboplastin time (PTT) that do not correct when mixed with normal control plasma lead to the presumption of the presence of a lupus anticoagulant (LA), sometimes called a non-specific inhibitor. To confirm, you would follow up with a standard LA profile using two testing platforms, usually one based on the dilute Russell viper venom time and another based on an LA-sensitive PTT reagent. Both are used with confirmatory high-phospholipid reagents.

A far less common possibility is a specific coagulation factor inhibitor. Because both the PT and PTT are prolonged, the inhibitor would have to be an anti-prothrombin, anti-factor V, or anti-factor X, the three members of the common coagulation pathway. These are rare, but could be a consideration if the patient is bleeding. Sometimes an anti-prothrombin or anti-factor V (or combination of the two) arises in response to previous surgical use of fibrin glue.

For details on mixing studies and LA confirmation, go to audio modules 7 and 8, also named Lupus Anticoagulant 1 and 2.

I hope this helps. Geo.

Comments (1)
Dec 3, 2010 2:13pm

One other thing to take into consideration is there

One other thing to take into consideration is there may be heparin in the sample. When we do mixing studies to work up a long APTT, we always do a Thrombin Time to rule out the presence of heparin. Heparin will also act like a non-specific inhibitor and give you a positive mixing study.

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