Isolated rise in aPTT is seen in?
**Core Concept**
An isolated rise in activated partial thromboplastin time (aPTT) indicates a problem with the intrinsic coagulation pathway, which involves factors VIII, IX, XI, and XII. This pathway is responsible for the activation of factor X, leading to the formation of thrombin and subsequent clot formation.
**Why the Correct Answer is Right**
An isolated rise in aPTT is seen in conditions that affect the intrinsic coagulation pathway, such as **lupus anticoagulant**. Lupus anticoagulant is an antibody that forms in the setting of systemic lupus erythematosus (SLE) and interferes with the binding of phospholipid to factor VIII, leading to an isolated prolongation of aPTT. Other conditions such as **deficiency of factors VIII, IX, XI, or XII** can also cause an isolated rise in aPTT.
**Why Each Wrong Option is Incorrect**
**Option A:** Heparin therapy would typically cause a prolongation of both aPTT and PT (prothrombin time), not an isolated rise in aPTT.
**Option B:** Factor V deficiency would primarily affect the prothrombin time (PT), leading to a prolongation of the International Normalized Ratio (INR).
**Option C:** Protein C deficiency would typically cause a prolongation of the prothrombin time (PT), not an isolated rise in aPTT.
**Clinical Pearl / High-Yield Fact**
Lupus anticoagulant is a classic cause of an isolated rise in aPTT, and its presence should prompt further investigation for underlying SLE.
**Correct Answer: D. Lupus anticoagulant**