A pediatric patient with prolonged PT and abnormal aPTT, and a mixing study that does not correct, should prompt consideration of:

A pediatric patient with prolonged PT and abnormal aPTT, and a mixing study that does not correct, should prompt consideration of:

• A. lupus anticoagulant
• B. acquired factor inhibitor
• C. dysfibrinogenemia
• D. DIC evaluation

Answer: (B)

When a mixing study with normal plasma fails to correct prolonged PT and aPTT, the situation points to an inhibitor rather than a simple factor deficiency. A deficiency is usually remedied by adding normal plasma, which supplies the missing factors and shortens the times. An inhibitor, however, neutralizes coagulation factors even in the mix, so the abnormal time persists. Among the options, an acquired factor inhibitor fits best. This is an autoantibody directed against a specific coagulation factor (often one in the common pathway, such as factor II, V, or X, or sometimes factor VIII). Because the inhibitor blocks the activity of the target factor, adding normal plasma doesn’t restore normal clotting times, leading to a non-correcting mixing study. This explains both the prolonged PT and the abnormal aPTT in a unified way. Lupus anticoagulant, while also a non‑correction type inhibitor, is a phospholipid‑dependent antibody that mainly affects certain phospholipid‑dependent assays and often presents with a different clinical pattern (more thrombotic risk than bleeding). Dysfibrinogenemia involves abnormal fibrinogen function and typically has additional clues on specific fibrinogen tests; mixing would not reliably fit the described pattern. DIC evaluation is important in a patient with abnormal coagulation tests, but the key diagnostic clue here is the non-correcting mixing study pointing toward an inhibitor, most consistent with an acquired factor inhibitor.

When a mixing study with normal plasma fails to correct prolonged PT and aPTT, the situation points to an inhibitor rather than a simple factor deficiency. A deficiency is usually remedied by adding normal plasma, which supplies the missing factors and shortens the times. An inhibitor, however, neutralizes coagulation factors even in the mix, so the abnormal time persists.

Among the options, an acquired factor inhibitor fits best. This is an autoantibody directed against a specific coagulation factor (often one in the common pathway, such as factor II, V, or X, or sometimes factor VIII). Because the inhibitor blocks the activity of the target factor, adding normal plasma doesn’t restore normal clotting times, leading to a non-correcting mixing study. This explains both the prolonged PT and the abnormal aPTT in a unified way.

Lupus anticoagulant, while also a non‑correction type inhibitor, is a phospholipid‑dependent antibody that mainly affects certain phospholipid‑dependent assays and often presents with a different clinical pattern (more thrombotic risk than bleeding). Dysfibrinogenemia involves abnormal fibrinogen function and typically has additional clues on specific fibrinogen tests; mixing would not reliably fit the described pattern. DIC evaluation is important in a patient with abnormal coagulation tests, but the key diagnostic clue here is the non-correcting mixing study pointing toward an inhibitor, most consistent with an acquired factor inhibitor.