Monocytes
Monocytes· also: Monocytes
Clinical Overview
Monocytes are large white blood cells that circulate in blood and migrate into tissues to become macrophages. They play a key role in phagocytosis of bacteria, fungi, and dead cells, antigen presentation, and coordination of the immune response. Monocytosis can be a clue to chronic infections or myeloid malignancy.
Why This Test Matters
Monocytosis (high monocytes) is associated with chronic bacterial infections like tuberculosis and subacute bacterial endocarditis, as well as inflammatory bowel disease and monocytic leukemias. Chronic myelomonocytic leukemia (CMML) is defined by persistent monocytosis above 1,000/µL. Monocytopenia is a hallmark of hairy cell leukemia.
Reference RangesWHO/IFCC standards
| Age Group | Reference Range | Unit | Notes |
|---|---|---|---|
| Adults (18–64) | 0.2 – 0.95 | ×10³/µL | — |
Also reported in: %.
What Causes Abnormal Results?
High Monocytes Causes
- Tuberculosis and other mycobacterial infections
- Subacute bacterial endocarditis
- Inflammatory bowel disease
- Sarcoidosis
- Chronic myelomonocytic leukemia (CMML)
- Recovery phase after neutropenia
Low Monocytes Causes
- Hairy cell leukemia (classically associated with monocytopenia)
- High-dose corticosteroid use
- Aplastic anemia
Signs & Symptoms to Watch For
How to Prepare for This Test
No preparation needed. Part of CBC differential.
Factors That Can Affect Results
- Recovery from acute infection or neutropenia (physiological monocytosis)
- Exercise (mild transient increase)
Related Topics
Frequently Asked Questions
What does a high monocyte count indicate?
Mildly elevated monocytes are most often seen during recovery from acute infections as the immune system clears cellular debris. Persistently high monocytes (above 1,000/µL for more than 3 months) should prompt investigation for chronic infections (TB, endocarditis), inflammatory conditions, or CMML. A bone marrow biopsy and flow cytometry are needed to rule out CMML.