Serum lysozyme has emerged as a valuable biomarker for monitoring disease progression and regression, particularly in cases of confirmed sarcoidosis. According to revised FAB (French, American, British) criteria, serum or urine lysozyme levels that are three times the normal limit fulfill one of the key diagnostic criteria for distinguishing M4/M5 acute myeloid leukemia with monocytic differentiation from M2 acute myeloblastic leukemia with maturation.
Lysozyme is a hydrolytic enzyme and bacteriolytic glycosidase, which, when present in high concentrations, can be detected as a distinctive cationic band during serum or urine protein electrophoresis. This enzyme is found in all three types of human neutrophil granules—azurophil, specific, and gelatinase. It is frequently elevated in cases of myelogenous leukemia and is notably increased in most instances of myelomonocytic and monocytic leukemia. The degree of elevation is proportional to the extent of monocytic differentiation and the overall tumor cell burden. Significant increases in lysozyme levels can lead to complications such as potassium wasting and hypokalemia. Immunoelectron microscopy has also detected lysozyme within the granules of both normal and leukemic eosinophils. However, elevated serum lysozyme levels alone may not conclusively indicate monocytic differentiation in acute myelogenous leukemia cases with eosinophilia. Importantly, serum lysozyme levels have also been utilized to predict central nervous system involvement in these types of leukemias.
In addition to leukemia, elevated serum lysozyme levels have been observed in various conditions, including tuberculosis and sarcoidosis. In a recent study, the sensitivity of serum lysozyme for predicting sarcoidosis was found to be 79%, significantly higher than the 59% sensitivity for serum angiotensin-converting enzyme (ACE) in the same study. Furthermore, lysozyme levels were shown to increase with the number of organs involved in sarcoidosis, although its specificity for the condition is lower compared to serum ACE. A turbidimetric method for measuring serum lysozyme activity has proven useful for distinguishing between infection and rejection in transplant recipients, further underscoring its diagnostic versatility.
Lysozyme, Serum
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