Lack of specificity of the limulus lysate test in the diagnosis of pyogenic arthritis.

The diagnosis of pyogenic arthritis may be difficult to confirm since culture results are sometimes negative. This study attempted to evaluate the utility of the limulus lysate assay for the early detection of pyogenic arthritis due to gram-negative organisms. Seven-one specimens of synovial fluid from 46 patients were evaluated for reactivity in the limulus test, pyrogenic responses in rabbits, total white blood cell count, total neutrophil count, total red blood cell count, and protein and glucose concentrations. All patients with culture-proven septic arthritis or presumptive septic arthritis had joint fluid specimens that yielded a positive result in the limulus assay (12 patients). However, 52.9% of patients (18 of 34) who had a nonseptic cause for their joint effusion also had a joint fluid specimen that was positive in the limulus test. A positive limulus test result showed a significant correlation with an elevated total white blood cell count (P less than 0.0005), an elevated absolute neutrophil count (P less than 0.0005), and a decreased concentration of glucose (P less than 0.005) in synovial fluid, and the production of fever in rabbits after injection of synovial fluid (P less than 0.05). Thus, this study suggests that a positive result in the limulus test on joint fluid is nonspecific for a septic process, but a negative result would be evidence against it.