When your doctor orders a "complete blood count with differential" (CBC with diff), the laboratory examines the different types of white blood cells circulating in your blood.

Monocytes are versatile cleanup cells that make up about 3-8% of your white blood cells (approximately 0.3 × 10⁹/L). They circulate in your blood briefly, then migrate into tissues where they transform into macrophages—large cells that engulf bacteria, dead cells, and debris.

High monocytes (monocytosis) can occur with chronic infections (like tuberculosis), inflammatory conditions, or certain blood disorders. Low monocytes are less common and usually not clinically significant on their own.