## **Core Concept**
The Prothrombin Quality Control (PQC) or Prothrombin Time Quality Control (PT QC) or Quality Control range for coagulation tests, often referred to in terms of INR (International Normalized Ratio) for monitoring warfarin therapy, involves understanding the therapeutic range for anticoagulation.

## **Why the Correct Answer is Right**
The therapeutic range for the International Normalized Ratio (INR) in patients on warfarin therapy is generally considered to be between **2.0 to 3.0**. This range is crucial because it balances the risk of thrombosis (if INR is too low) against the risk of bleeding (if INR is too high).

## **Why Each Wrong Option is Incorrect**
- **Option A:** 3.0 - While some specific conditions may warrant a slightly higher INR range, for most indications, an INR consistently above 3.0 increases the risk of bleeding without providing additional protection against thrombosis.
- **Option D:** > 4.0 - This is generally considered too high for most patients on warfarin therapy, significantly increasing the risk of major bleeding.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that for most patients on warfarin for conditions like atrial fibrillation or venous thromboembolism, the target INR range is **2.0-3.0**. However, specific conditions such as mechanical heart valves may require a higher INR range, typically **2.5-3.5**.

## **Correct Answer:** C. 2.0-3.0