How is correction of a mixing study determined

Due to the variation in instruments and reagents used by individual laboratories, each laboratory must establish its own optimal reference cut-off value from known samples to use as a criterion for the interpretation of results.

Unfortunately, there is no magical formula for determining a mixing study correction. Most agree though that each lab should have a standard process for performing and interpreting mixing studies. References: 1 Ledford-Kraemer, Marlies. First Edition Lupus Anticoagulant and the Lab. June , pg Am J Clin Pathol ; Tags: anticoagulants , blood clotting , coagulation , factor deficiencies , Hematology , inhibitors , laboratory , mixing study , prolongation , PT , PTT , reagents , thrombosis.

Determining the cause of the prolongation It is important to determine if the cause of the prolongation is due to a factor deficiency or circulating anticoagulant inhibitor. Congenital vs. What if the mixing study does not correct? The prolongation may be due to an inhibitor. Are the patients receiving anticoagulants? Board review style question 1.

Prothrombin time PT and activated partial thromboplastin time aPTT are performed on a 64 year old man. The patient is taking no anticoagulants or other medications. The results of a mixing study are Patient aPTT: 51 s reference range 38 - 42 s Immediate aPTT mixing study: 36 s Which of the following is the next best test to order?

Board review style answer 1. Factor VIII activity. The mixing study indicates a corrected result which suggests a factor deficiency as a cause of the prolonged aPTT. Lupus anticoagulant testing could also be considered, as some weak lupus anticoagulants may show apparent correction in mixing studies. Comment Here Reference: Mixing studies. Board review style question 2. Coagulation laboratory tests are drawn on a 35 year old woman with the recent diagnosis of an autoimmune disease.

The physician ordered a mixing study after the original results revealed a prolonged activated partial thromboplastin time aPTT. Board review style answer 2. Lupus anticoagulant. This result suggests an inhibitor that overcomes the normal coagulation factors in the patient sample as well as the NPP. Lupus anticoagulants behave as nonspecific inhibitors in aPTT mixing studies and are a common cause of unexpected aPTT prolongation.

The recent history of an autoimmune disorder diagnosed in a young woman would also raise concern for a lupus anticoagulant as an explanation for her prolonged aPTT. Sign up for our Email Newsletters. Click here for information on linking to our website or using our content or images.