**Question:** PTT is prolonged in all except

A. Heparin therapy (inhibits coagulation)
B. Factor V Leiden mutation (increased procoagulant activity)
C. Vitamin K deficiency (decreased anticoagulant activity)
D. Protein C deficiency (decreased anticoagulant activity)

**Correct Answer:** Heparin therapy (inhibits coagulation)

**Core Concept:**
Prolonged Partial Thromboplastin Time (PTT) is a test used to assess the intrinsic and common coagulation pathways, as well as the presence of anticoagulants or inhibitors. The normal PTT ranges between 25-40 seconds.

**Why the Correct Answer is Right:**
Heparin is a potent anticoagulant drug that inhibits the activation of factor X through the inhibition of factor Xa. By prolonging the PTT, heparin is used to prevent and treat thromboembolic events. Therefore, it is an exception to the general rule that PTT is prolonged in conditions affecting coagulation or anticoagulants.

**Why Each Wrong Option is Incorrect:**

A. Vitamin K deficiency (C.O.B.R.A.H., Coagulation, Omega, Bile Acid, Reverse, Hemostasis) results in decreased anticoagulant activity and leads to a prolonged PTT.

B. Factor V Leiden mutation (C.O.B.R.A.H., Coagulation, Omega, Bile Acid, Reverse, Hemostasis) increases procoagulant activity, which results in a prolonged activated partial thromboplastin time (aPTT), not PTT.

C. Protein C deficiency (C.O.B.R.A.H., Coagulation, Omega, Bile Acid, Reverse, Hemostasis) also results in decreased anticoagulant activity and leads to a prolonged PTT.

D. Heparin therapy (as explained above) is an exception to the rule that PTT is prolonged in conditions affecting coagulation or anticoagulants.

**Clinical Pearl:**
Understanding the normal and abnormal PTT values aids in diagnosing and managing patients with bleeding and thrombotic disorders. Monitoring PTT during heparin therapy ensures the appropriate dosing and prevents complications like bleeding.