Investigations and diagnosis in gout

• serum urate - may be raised
  • measure the serum urate level in people with symptoms and signs of gout to confirm the clinical diagnosis (serum urate level of 360 micromol/litre [6 mg/dl] or more) (1)
    • if serum urate level is below 360 micromol/litre (6 mg/dl) during a flare and gout is strongly suspected, repeat the serum urate level measurement at least 2 weeks after the flare has settled
• aspiration and polarized light examination of synovial fluid - shows negatively birefringent crystals
  • consider joint aspiration and microscopy of synovial fluid if a diagnosis of gout remains uncertain or unconfirmed (1)
• radiology
  • if joint aspiration cannot be carried out or the diagnosis of gout remains uncertain, consider imaging the affected joints with X-ray, ultrasound or dual-energy CT (1)
• leucocytosis and raised ESR and CRP during the acute attack

Notes:

• in gout serum urate levels may be normal during an acute attack and thus the optimal time for measurement is about two weeks after a flare resolves (2)
• other tests to consider (2):
  • assessment of other CV risk factors - fasting lipid profile and glucose
  • depending on the clinical scenario - FBC, blood film, B12 and TFTs as on occasion elevated serum urate levels may be seen in conditions such as lymphoproliferative and myloproliferative disorders, B12 deficiency, lead exposure and hypothyroidism
    
    
• EULAR recommendation for diagnosis of gout (3) The European League Against Rheumatism (EULAR) published the following evidence-based guidelines for the diagnosis of patients with gout (3):
  • rapid development of severe pain, swelling, and tenderness that reaches its maximum within 6 to 12 hours, especially with overlying erythema in acute monoarticular attacks of the lower extremities - is highly suggestive of crystal inflammation (although not specific for gout)
  • a clinical diagnosis alone is a reasonable alternative in patients with typical presentations of gout but a definite diagnosis of gout is made when of MSU crystals are demonstrated in synovial fluid or tophus aspirates constitutes
  • serum urate acid (SUA) levels do not confirm or exclude gout (although this is the most important risk factor for gout), since many people with hyperuricemia do not develop gout, and SUA levels may be normal during acute attacks.
  • a routine search for MSU crystals is always better to look for in synovial fluid samples that were obtained from the undiagnosed inflamed joints.
  • incase of a doubtful diagnosis, the best way to make a definite diagnosis is by identification of MSU crystals from asymptomatic joints,during the intercritical period.
  • since gout and sepsis may coexist with each other,it is always best to perform a gram staining and a culture of the synovial fluid even after MSU crystals have been identified in our diagnosis,to rule out septic arthritis.
  • assessment of renal UA excretion should, however, be considered in those with young-onset gout (aged < 25 years) or in patients with a family history of young-onset gout.In others,this test rarely needs to be done.
  • a high incidence of renal stones are present in people with gout hence,those with stones should have a lithogenic workup
  • radiographs are not used to confirm the diagnosis of early or acute gout and should be done only in the case of suspecting a fracture. But,this may be useful for differential diagnosis and may show typical features in gout.
  • it is highly important to assess the risk factors for gout,which includes:
    • features of metabolic syndrome ( hyperglycemia, hyperlipidemia, hypertension and obesity),
    • chronic kidney disease (CKD),
    • medications(diuretics)
    • family history
    • and lifestyle

Reference:

• 1. NICE (June 2022). Gout: diagnosis and management
• 2. Pulse (1/4/09), 29.
• 3. Hamburger M. 2011 Recommendations for the diagnosis and management of gout and hyperuricemia. Postgrad Med. 2011;123(6 Suppl 1):3-36.