D-lactic acid in synovial fluid. A rapid diagnostic test for bacterial synovitis.

OBJECTIVE

To analyze the usefulness of D-lactic acid levels in synovial fluid (SF) as a rapid test to support the early diagnosis of bacterial arthritis (BA).

METHODS

A simple modification of the enzyme method used for measuring L-lactic acid was used to analyze levels of D-lactic acid in SF from 20 cases of BA. Results were compared with those from 99 noninfectious arthritis, which included 90 inflammatory SF samples. Total white blood cell count (WBC), percentage of polymorphonuclears (% PMN) and gram stains were also determined.

RESULTS

D-lactic acid levels were significantly higher in BA than in noninfectious arthritis. Using a cutoff value of 0.05 mM, 85% of the SF samples from BA had a positive test for D-lactic acid compared with 4% of the control group. The overall sensitivity of the assay was 85% with a specificity of 96%, showing a positive predictive value for BA of 81% and a negative predictive value of 97%.

CONCLUSION

The data presented suggest that D-lactic acid is an accurate, easy test that can be carried out in any laboratory, to support the early diagnosis of BA.