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In Reply: Our search of the literature identified 6 studies^1-5 that address synovial fluid lactic acid as a clinical test for septic arthritis. Previous studies⁶ suggest that although synovial lactic acid dehydrogenase (LDH) by enzymatic analysis may be sensitive for detecting bacterial infection, it is not specific, and elevated synovial LDH levels may be observed in noninfectious inflammatory and crystal-induced arthropathies, such as rheumatoid arthritis and gout.

The identified studies were heterogeneous in their measurement of lactic acid. Brook et al,¹ Gratacós et al,² and Riordan et al⁵ evaluated lactic acid concentration by gas liquid chromatography, while Mossman et al³ and Shmerling et al⁴ assessed LDH by enzymatic analysis. Furthermore, Gratacós et al evaluated D-lactic acid, an optical isomer of L-lactic acid. The other studies did not identify if they were referring to D-lactic acid, L-lactic acid, or both. Most studies of synovial lactic acid were . . . [Full Text of this Article]

Mary E. Margaretten, MD
mary.margaretten@ucsf.edu
Division of Rheumatology

Jeffrey Kohlwes, MD, MPH; Stephen Bent, MD
Department of Medicine
University of California
San Francisco

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