Investigations for acute inflammatory monoarthritis in adults

For detailed advice on the utility of investigations for suspected inflammatory monoarthritis, see Investigations for musculoskeletal symptoms in adults.

Note: Urgent joint aspiration and synovial fluid analysis is the most important investigation in acute inflammatory monoarthritis.

Urgent joint aspiration and synovial fluid analysis is the most important investigation for acute inflammatory monoarthritis. This is to exclude septic arthritis, assess for crystals or blood, or define other significant inflammatory arthropathy. See Utility of joint aspiration and synovial fluid analysis for rheumatological diseases for a detailed discussion.

For people with a suspected haemarthrosis (who are usually anticoagulated or have haemophilia), seek expert advice from a haematologist before joint aspiration because the patient will require preprocedural coagulation-factor replacement.

Blood investigation results are usually nonspecific in acute monoarthritis. Pitfalls in the interpretation of blood investigation results for acute monoarthritis in adults include:

  • normal white cell count (WCC), serum C-reactive protein (CRP) concentration or erythrocyte sedimentation rate (ESR) do not exclude infection, especially in older or immunocompromised patients
  • blood cultures are only positive in about 50% of cases of nongonococcal septic arthritis
  • testing for autoantibodies, such as rheumatoid factor (RF) and antinuclear antibodies (ANA), is rarely helpful in differentiating an acute monoarthritis
  • normal serum uric acid concentration may be seen in people with acute gout; conversely, hyperuricaemia alone is insufficient to diagnose gout.

If reactive arthritis associated with a sexually transmitted infection (STI) is suspected, consider investigating for an STI.

Plain X-ray may be indicated if a monoarthritis is associated with trauma (eg to rule out a juxta-articular fracture). If initial imaging is normal but the suspicion of a fracture or acute internal derangement remains, more specialised imaging may be warranted. See Utility of imaging for rheumatological diseases for more detail.