Lactic acid concentrations in the synovial fluid of 84 patients with acute monoarticular arthritis were determined by gas liquid chromatography. Lactic acid values in 27 cases of nongonococcal septic arthritis were strikingly higher (mean 1170 mg/100 ml) than in 45 cases of inflammatory or degenerative arthritis (mean 34 mg/100 ml), as well as in 12 cases of gonococcal arthritis (mean 27 mg/ 100 ml). With the proper equipment, determination of lactic acid can be a relatively rapid, reliable procedure. Synovial fluid lactic acid concentrations therefore can be used as a rapid, supplemental diagnostic aid in differentiating nongonococcal septic arthritis from both gonococcal and nonseptic acute arthritis.

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The concentration of lactic acid in cerebrospinal fluid (CSF) was determined by gas-liquid chromatography in 205 samples of CSF from 97 patients with or without infections of the central nervous system. Patients without infection or those with nonbacterial (presumably viral) meningitis consistently had low concentrations of lactic acid in CSF (i.e., less than or equal to 35 mg/100 ml), whereas patients with bacterial or tuberculosis meningitis consistently had concentrations of lactic acid in CSF of greater than 35 mg/100 ml. There was no overlap in concentrations of lactic acid between these two groups. Further, lactic acid concentrations in CSF from patients partially treated for meningitis were generally greater than 35 mg/100 ml through the third day of therapy and, thereafter, progressively declined to less than 20 mg/100 ml by the seventh to 10th day of therapy. Relapse of bacterial infection was consistently documented by a recurrence of an increased concentration of lactic acid in CSF. Preliminary experience with determination of the concentration of lactic acid in CSF suggests that it may be useful in distinguishing bacterial (with or without positive cultures) and tuberculous meningitis from meningitis due to nonbacterial causes.