TAILIEUCHUNG - Chapter 059. Bleeding and Thrombosis (Part 9)

Mixing Studies Mixing studies are used to evaluate a prolonged aPTT or, less commonly PT, to distinguish between a factor deficiency and an inhibitor. In this assay, normal plasma and patient plasma are mixed in a 50:50 ratio, and the aPTT or PT is determined immediately and after incubation at 37oC for varying times, typically 30, 60, and/or 120 min. With isolated factor deficiencies, the aPTT will correct with mixing and stay corrected with incubation. With aPTT prolongation due to a lupus anticoagulant, the mixing and incubation will show no correction. In acquired neutralizing factor antibodies, such as an acquired. | Chapter 059. Bleeding and Thrombosis Part 9 Mixing Studies Mixing studies are used to evaluate a prolonged aPTT or less commonly PT to distinguish between a factor deficiency and an inhibitor. In this assay normal plasma and patient plasma are mixed in a 50 50 ratio and the aPTT or PT is determined immediately and after incubation at 37oC for varying times typically 30 60 and or 120 min. With isolated factor deficiencies the aPTT will correct with mixing and stay corrected with incubation. With aPTT prolongation due to a lupus anticoagulant the mixing and incubation will show no correction. In acquired neutralizing factor antibodies such as an acquired factor VIII inhibitor the initial assay may or may not correct immediately after mixing but will prolong or remain prolonged with incubation at 37oC. Failure to correct with mixing can also be due to the presence of other inhibitors or interfering substances such as heparin fibrin split products and paraproteins. Specific Factor Assays Decisions to proceed with specific clotting factor assays will be influenced by the clinical situation and the results of coagulation screening tests. Precise diagnosis and effective management of inherited and acquired coagulation deficiencies necessitate quantitation of the relevant factors. When bleeding is severe specific assays are often urgently required to guide appropriate therapy. Individual factor assays are usually performed as modifications of the mixing study where the patient s plasma is mixed with plasma deficient in the factor being studied. This will correct all factor deficiencies to 50 thus making prolongation of clot formation due to a factor deficiency dependent on the factor missing from the added plasma. Testing for Antiphospholipid Antibodies Antibodies to phospholipids cardiolipin or phospholipid-binding proteins P2-microglobulin and others are detected by ELISA. When these antibodies interfere with phospholipid-dependent coagulation tests they are termed lupus

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