**Core Concept**
Neutropenia is a condition characterized by an abnormally low count of neutrophils, a type of white blood cell crucial for fighting infections. The severity of neutropenia is often classified based on the absolute neutrophil count (ANC) per microliter of blood, with moderate neutropenia being a significant concern for patients.

**Why the Correct Answer is Right**
Moderate neutropenia is generally defined as an ANC of 500-1000 cells per microliter. At this level, patients are at increased risk of developing severe infections, particularly bacterial infections. The reduced number of neutrophils impairs the body's ability to fight off pathogens, making it essential to take preventive measures to avoid infection.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because an ANC of 100-500 cells per microliter is actually considered severe neutropenia, not moderate.
**Option B:** This option is incorrect because an ANC of 1000-2000 cells per microliter is considered mild neutropenia, not moderate.
**Option C:** This option is incorrect because an ANC of < 100 cells per microliter is considered life-threatening severe neutropenia. **Clinical Pearl / High-Yield Fact** When interpreting ANC results, it's essential to consider the patient's clinical context and potential sources of neutropenia, such as chemotherapy, infections, or bone marrow disorders. **Correct Answer: C. < 100 cells/μL**