Synovial Fluid For AFB

Function

This test involves the microscopic examination (smear) and culture of synovial fluid (joint fluid) to detect Acid-Fast Bacilli (AFB), primarily Mycobacterium tuberculosis. Tuberculous arthritis is a form of extrapulmonary tuberculosis that affects the joints, usually the knee or hip.

Why it is Ordered

It is ordered for patients with chronic monoarthritis (inflammation of a single joint) that does not respond to standard treatments for rheumatoid arthritis or common bacterial infections. Symptoms include joint swelling, pain, and restricted range of motion, often without significant fever.

Associated Conditions

• Tuberculous Arthritis: A slow-progressing infection of the joint space.
• Non-tuberculous Mycobacterial (NTM) Infection: Less common, but can occur after trauma or surgery.
• Systemic Tuberculosis: If joint AFB is positive, it often indicates the patient has a primary focus of infection in the lungs.

Summary

Identifying AFB in synovial fluid is diagnostic for mycobacterial joint disease, which requires a specific and prolonged course of anti-tubercular medications compared to standard septic arthritis.