What labs should I order when suspecting gout?

Laboratory Tests for Suspected Gout

When suspecting gout, synovial fluid analysis for monosodium urate (MSU) crystals should be the primary diagnostic test ordered, as it is the gold standard for definitive diagnosis of gout. 1

Diagnostic Approach

Step 1: Synovial Fluid Analysis

• Synovial fluid aspiration and examination for MSU crystals is the definitive diagnostic test for gout 1
• Should be performed in any patient with undiagnosed inflammatory arthritis 1
• Gram stain and culture of synovial fluid should also be performed when septic arthritis is suspected, as gout and sepsis may coexist 1

Step 2: Serum Laboratory Tests

If synovial fluid analysis is not feasible, order:

1. Serum uric acid level

   • Important to note: A normal serum uric acid level does not exclude gout, especially during acute attacks 1
   • Hyperuricemia alone is insufficient for diagnosis as many people with elevated uric acid levels never develop gout 1

2. Additional laboratory tests to assess for comorbidities and risk factors:

   • Complete blood count
   • Renal function tests (BUN, creatinine)
   • Liver function tests
   • Lipid profile
   • Fasting glucose 1

3. In selected patients:

   • Renal uric acid excretion (24-hour urine collection for uric acid) - particularly in patients with:
     • Family history of young-onset gout
     • Onset of gout under age 25
     • History of renal calculi 1

Clinical Correlation

When synovial fluid analysis is not possible, clinical features that support a diagnosis of gout include:

• Monoarticular involvement of first metatarsophalangeal joint (podagra) or ankle
• Previous similar acute arthritis episodes
• Rapid onset of severe pain and swelling (maximum within 24 hours)
• Erythema over the affected joint
• Male gender
• Associated cardiovascular diseases
• Hyperuricemia 1

Imaging Considerations

If clinical diagnosis remains uncertain and crystal identification is not possible:

• Ultrasound - more helpful than plain radiographs for acute gout:

  • Look for "double contour sign" (hyperechoic irregular enhancement over cartilage)
  • Can detect tophi not evident on clinical examination 1

• Plain radiographs - limited value for early or acute gout but may show typical features in chronic gout 1

Common Pitfalls to Avoid

1. Relying solely on serum uric acid levels - both false positives (hyperuricemia without gout) and false negatives (normal levels during acute attacks) are common 1

2. Failing to rule out infection - always consider septic arthritis, which may coexist with gout 1

3. Missing comorbidities - systematic assessment for associated conditions is essential, including obesity, renal impairment, hypertension, heart disease, diabetes, and dyslipidemia 1

4. Delaying diagnosis - missed or delayed diagnosis can result in longer hospitalizations and poorer outcomes 1

By following this structured approach to laboratory testing for suspected gout, you can achieve accurate diagnosis and appropriate management of this common inflammatory arthritis.