In suspected septic arthritis, what is the most urgent initial diagnostic step?

• A. Joint aspiration for synovial fluid analysis and culture
• B. MRI of the joint
• C. X-ray of the joint
• D. Serum uric acid

Answer: (A)

The key idea is that confirming infection quickly is essential in suspected septic arthritis to prevent rapid joint damage and to guide targeted therapy. The most urgent initial step is obtaining joint fluid through aspiration for synovial fluid analysis and culture. Analyzing the fluid directly provides definitive evidence of infection, shows the cell count and neutrophil predominance, and allows Gram stain and culture to identify the organism and its sensitivities. This information is what drives appropriate antibiotic treatment and helps distinguish septic arthritis from inflammatory or crystal-induced arthritis.

Imaging like MRI or X-ray won’t confirm infection promptly or definitively; they can show a joint effusion or structural changes but are not diagnostic in the acute setting. Serum uric acid isn’t reliable for diagnosing septic arthritis and can be misleading.