This laboratory test measures the concentration of the enzyme lysozyme, also known as mouramidase, in blood serum. Lysozyme is a bacteriostatic enzyme secreted primarily by phagocytic cells (macrophages and monocytes) and neutrophils. It breaks down the cell wall of Gram-positive bacteria. Measuring its level is used as an indirect indicator of activated phagocytic cell mass and activity, and in the differential diagnosis of certain myeloproliferative disorders and inflammatory bowel diseases.