Which situation would most likely cause a falsely short aPTT result?

Which situation would most likely cause a falsely short aPTT result?

• A. Exposure of the plasma to erythrocytes for several hours
• B. Prolonged refrigeration
• C. Immediate testing after collection
• D. Use of EDTA as anticoagulant

Answer: (A)

A falsely short aPTT typically results from pre-analytical activation of the coagulation system. When plasma is left in contact with erythrocytes for several hours, red cells can release phospholipids and other procoagulant debris. These phospholipid surfaces augment the assembly of coagulation complexes that drive the intrinsic pathway, shortening the time to clot formation measured by the aPTT. In other words, extra surface on which the cascade can assemble makes the test appear quicker than it truly is, giving a falsely low (short) result. By comparison, prolonged refrigeration slows enzymatic reactions and can degrade clotting factors, leading to longer (prolonged) times rather than shorter. Testing immediately after collection is not a reliable source of a falsely short result and can introduce other pre-analytical errors; using EDTA as anticoagulant prevents clotting in the plasma entirely for this type of assay, so it would not yield a valid aPTT result and certainly not a falsely short one.

A falsely short aPTT typically results from pre-analytical activation of the coagulation system. When plasma is left in contact with erythrocytes for several hours, red cells can release phospholipids and other procoagulant debris. These phospholipid surfaces augment the assembly of coagulation complexes that drive the intrinsic pathway, shortening the time to clot formation measured by the aPTT. In other words, extra surface on which the cascade can assemble makes the test appear quicker than it truly is, giving a falsely low (short) result.

By comparison, prolonged refrigeration slows enzymatic reactions and can degrade clotting factors, leading to longer (prolonged) times rather than shorter. Testing immediately after collection is not a reliable source of a falsely short result and can introduce other pre-analytical errors; using EDTA as anticoagulant prevents clotting in the plasma entirely for this type of assay, so it would not yield a valid aPTT result and certainly not a falsely short one.