Lactic acid can be formed as a "blind alley" in the metabolic degradation of glucose, especially under anaerobic conditions.

The presence of bacterial infection in a closed body cavity induces elevated levels of lactic acid, as is evident in bacterial and fungal infections in the meninges, joints, peritoneum, and pleura. Although measurement of lactate levels is not a test without faults, it is still a valuable tool in the early recognition of bacterial infections of various body cavities and can assist in the differentiation between infectious and noninfectious conditions.

False-positive readings can be obtained with severe anoxia of the CNS, and with irritation of the peritoneal or pleural cavities due to metastases. False-negative values can be obtained in gonococcal arthritis. Table 1 presents accepted normal values for lactic acid in various body sites and the levels of lactic acid than can signify the presence of infection. Further work is still needed to provide better understanding of the mechanisms that cause changes in concentrations of lactic acid.

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Brook I. (1981) The importance of lactic acid levels in body fluids in the detection of bacterial infections. Rev Infect Dis. 1981 May-Jun;3(3):470-8.