Diagnostic value of serum and synovial procalcitonin in acute arthritis: a prospective study of 42 patients.

OBJECTIVE To determine the diagnostic value of serum and synovial procalcitonin (PCT) for bacterial arthritis and to determine the cellular origin of synovial PCT. METHODS A prospective study enrolled 42 patients with acute arthritis including 11 bacterial arthritis, 18 rheumatoid arthritis and 13 crystal induced arthritis. Diagnostic values of serum and synovial PCT levels were determined by a immunoluminometric assay (Lumitest PCT) and compared to those of classical inflammatory markers (C-reactive protein, erythrocyte sedimentation rate, synovial fluid cellularity and both serum and synovial IL-6 and TNF alpha). Using fibroblast-like synoviocyte (FLS) cultures derived from rheumatoid arthritis (n = 4) and osteo-arthritis (n = 3) synovium, with or without stimulation by lipopolysaccharid or recombinant streptococcal protein 1/II, we attempted to determine whether synovial cells could be a source of PCT. RESULTS Serum PCT was the best parameter to distinguish patients with acute bacterial arthritis from patients with crystal induced arthritis or rheumatoid arthritis. In setting of an acute arthritis serum PCT (> 0.5 ng/mL) achieved 55% sensitivity and 94% specificity for the diagnosis of bacterial arthritis, while CRP (> 50 mg/L) had 100% sensitivity but poor specificity (40%). Serum PCT appeared to be higher in patients with septic arthritis resulting from "systemic infection" than in cases resulting from direct inoculation. Synovial PCT was not useful to discriminate between infectious and non infectious arthritis in clinical practice. PCT could not be detected at significant levels in the conditioned medium from fibroblast-like synoviocyte cultures. CONCLUSION Serum PCT is a poorly sensitive but specific marker of bacterial arthritis. Use of serum PCT in association with CRP could nevertheless be useful in an emergency situation for the diagnosis of bacterial arthritis.