What is the appropriate work‑up for a patient in whom gout is suspected?

Gout Work-Up

The work-up for suspected gout should prioritize joint aspiration with synovial fluid analysis for monosodium urate (MSU) crystal identification as the definitive diagnostic test, but when this is not feasible, combine clinical diagnostic criteria with ultrasound imaging to achieve diagnostic accuracy exceeding 80%. 1, 2

Step 1: Joint Aspiration and Synovial Fluid Analysis (Gold Standard)

Perform arthrocentesis whenever possible, particularly in the following scenarios:

• First suspected gout attack 2
• Atypical clinical presentation 2
• Septic arthritis cannot be clinically excluded 1, 2
• Diagnosis remains uncertain after clinical assessment 1

Key technical points:

• MSU crystals appear as needle-shaped, negatively birefringent crystals under polarized light microscopy with sensitivity 63-78% and specificity 93-100% 2
• Always perform Gram stain and culture even when MSU crystals are identified, as gout and septic arthritis can coexist 2
• Synovial fluid can detect MSU crystals in approximately 70% of patients during intercritical periods 2
• Joint aspiration is technically difficult in smaller joints and rarely performed in primary care settings 2

Step 2: Clinical Diagnosis (When Aspiration Not Feasible)

Use the following highly suggestive clinical features to achieve >80% diagnostic accuracy:

• Monoarticular involvement of the first metatarsophalangeal joint (podagra) with sensitivity 96%, specificity 97%, likelihood ratio 30.64 2
• Rapid onset of severe pain reaching maximum intensity within 6-12 hours 2
• Erythema over the affected joint 1, 2
• Previous similar acute arthritis episodes 1, 2
• Male gender 1
• Associated cardiovascular diseases 1
• Presence of hyperuricemia 1, 2

Critical caveat: Do not diagnose gout based on hyperuricemia alone—approximately 10% of patients with acute gout have normal serum uric acid levels during an attack, and only 22% of asymptomatic patients with serum uric acid >9 mg/dL develop gout over 5 years. 1, 2

Step 3: Imaging Studies (When Clinical Diagnosis Uncertain)

Ultrasound is the preferred first-line imaging modality:

• Sensitivity 74-83% and specificity 88% for detecting the "double contour sign" on cartilage surfaces 2
• Sensitivity 65% and specificity 80% for detecting tophi 2
• Always scan the first metatarsophalangeal joint bilaterally, even if asymptomatic 2
• Performs better in late disease (>2 years duration) with 63% sensitivity compared to 50% in early disease 2
• Can assess inflammation, making it superior to DECT for monitoring disease activity 2

Dual-Energy CT (DECT) as second-line imaging:

• Sensitivity 85-100% and specificity 83-92% for detecting MSU crystal deposition 1, 2
• More expensive and involves radiation exposure 2
• Less sensitive in patients with shorter history of flares (<2 years) 2
• Consider when ultrasound is negative but clinical suspicion remains high in patients with disease duration >2 years 2

Plain radiographs have limited diagnostic value:

• Useful only for assessing chronic structural damage and ruling out alternative diagnoses 1, 2
• Should not be the primary diagnostic imaging modality 2

Step 4: Laboratory Evaluation

Essential laboratory tests:

• Serum uric acid level: Measure immediately, but recognize that hyperuricemia alone has only 53-61% specificity for gout, and normal levels do not exclude acute gout 2
• Inflammatory markers (ESR, CRP) and complete blood count: Assess inflammation severity and rule out infection 2
• Renal function (creatinine, eGFR): Essential for treatment planning and identifying chronic kidney disease as a risk factor 2
• 24-hour urinary uric acid excretion: Indicated in patients with family history of young-onset gout, onset under age 25, or history of renal calculi 2

Step 5: Risk Factor and Comorbidity Assessment

Screen for modifiable risk factors:

• Chronic kidney disease (relative risk 4.95) 1, 2
• Obesity (relative risk 3.81) 1, 2
• Hypertension (relative risk 3.93) 1, 2
• Medications: diuretics (relative risk 1.72), low-dose aspirin, cyclosporine, tacrolimus 1, 2
• Alcohol consumption, particularly beer and spirits 1
• Diet high in meat, shellfish, and high-fructose corn syrup 1, 2

Systematically assess for associated comorbidities:

• Renal impairment 1
• Ischemic heart disease 1
• Heart failure 1
• Diabetes 1
• Dyslipidemia 1

Common Pitfalls to Avoid

• Do not rely on serum uric acid alone for diagnosis—it may be normal during acute attacks and many patients with hyperuricemia never develop gout 2
• Do not skip Gram stain and culture when crystals are identified—septic arthritis and gout can coexist 2
• Do not use plain radiographs as the primary diagnostic tool—they provide no information on crystal deposition or acute inflammation 2
• Do not assume ultrasound will be positive in early disease (<2 years)—sensitivity is only 50% for double contour sign in this population 2
• Ensure imaging is performed and interpreted by trained healthcare professionals to ensure accuracy 2