Which laboratory tests and imaging studies are most useful in confirming a diagnosis of septic arthritis?

Laboratory tests most useful in confirming septic arthritis include:

• Synovial fluid analysis obtained by joint aspiration, including microscopy and culture, to identify causative organisms and confirm infection.
• Blood cultures may be helpful, especially if systemic infection is suspected.
• Routine blood tests such as inflammatory markers (e.g., CRP, ESR) and white blood cell count support the diagnosis but are not definitive.

Imaging studies useful in septic arthritis diagnosis include:

• X-ray of the affected joint to assess for joint space narrowing, bone destruction, or other changes.
• Ultrasound can be used to detect joint effusion and guide aspiration.
• Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) may be used for detailed assessment, especially if bone or soft tissue involvement is suspected.

These investigations help confirm septic arthritis by identifying infection in the joint and assessing the extent of joint and surrounding tissue involvement.

Note: Joint aspiration with synovial fluid analysis is the key diagnostic test to confirm septic arthritis and differentiate it from other causes of joint inflammation such as gout or bursitis NICE CKS,NICE NG51,NICE NG219,NICE NG33.