Which one of the following laboratory tests differentiates leukemoid reaction from chronic myeloid leukemia?

**Core Concept**
Leukemoid reaction and chronic myeloid leukemia (CML) are two conditions that can cause an increase in white blood cell count, but they have distinct underlying pathologies. A leukemoid reaction is a reactive process, typically in response to infection or inflammation, whereas CML is a clonal disorder of the myeloid cells.

**Why the Correct Answer is Right**
The correct answer is **B. Leukocyte alkaline phosphatase (LAP) score**. In a leukemoid reaction, the LAP score is usually high (> 200), whereas in CML, the LAP score is typically low ( 200) in a patient with an elevated white blood cell count suggests a leukemoid reaction, whereas a low LAP score (< 20) suggests CML. **Correct Answer:** B. Leukocyte alkaline phosphatase (LAP) score.

✓ Correct Answer: A. LAP (leukocyte alkaline phosphatase)