What is the diagnostic workup for gout?

Diagnostic Workup for Gout

Gold Standard Diagnosis

Synovial fluid aspiration with identification of monosodium urate (MSU) crystals under polarized light microscopy remains the definitive diagnostic test for gout, with sensitivity and specificity approaching 100% when performed by experienced operators. 1

• MSU crystals appear as needle-shaped, negatively birefringent crystals under polarizing microscopy 1
• Even when MSU crystals are identified, perform Gram stain and culture simultaneously, as gout and septic arthritis may coexist 1
• Joint aspiration is technically difficult and painful in smaller joints, which limits its routine use in primary care settings 2

Clinical Diagnostic Approach (When Aspiration Not Feasible)

High-Yield Clinical Features

When joint aspiration is not feasible, clinical diagnosis relies on highly suggestive features that include monoarticular arthritis affecting the first metatarsophalangeal joint (podagra), rapid onset of severe pain reaching maximum intensity within 24 hours, erythema over the affected joint, male gender, history of previous similar attacks, and cardiovascular comorbidities. 1

Validated Clinical Algorithms

• The 2015 ACR/EULAR Gout Classification Criteria provide the most robust clinical diagnostic framework, with sensitivity of 92% and specificity of 89% (including imaging) or 85% and 78% (excluding imaging). 2
• Entry criterion: at least 1 episode of swelling, pain, or tenderness in a peripheral joint 2
• If MSU crystals not identified, apply hierarchical scoring system across clinical, laboratory, and imaging domains 2
• Score ≥8 points is diagnostic for gout 2
• Key high-value features include presence of tophi (OR 7.29), resolution of pain by 2 weeks (OR 3.58), and double contour sign on ultrasound (OR 7.23) 2

Clinical Algorithms Performance

• Multiple clinical algorithms demonstrate sensitivities and specificities >80% for diagnosing early-onset gout compared to synovial fluid analysis 2
• These algorithms have high sensitivity in patients with recent-onset attacks—the population most likely seen in primary, urgent, or emergency care settings 2
• Critical caveat: The relatively low specificity of clinical algorithms raises risk for missed diagnosis of septic arthritis, which has similar initial presentation. 2
• If septic arthritis is in the differential diagnosis, aspiration for Gram stain and culture remains essential regardless of clinical suspicion for gout 2

Laboratory Testing

Serum Uric Acid

• Serum uric acid measurement is essential but not diagnostic on its own 1
• Many patients with hyperuricemia never develop gout 1
• Serum uric acid may be normal during an acute gout attack, limiting its diagnostic utility in the acute setting 1
• Contributes variable points to ACR/EULAR criteria based on level (including negative points for lower values) 2

Imaging Studies

Ultrasound

Ultrasound is the preferred initial imaging modality when available, with the "double contour sign" having 95% specificity and considered pathognomonic when present. 3

• Overall ultrasound sensitivity ranges from 37% to 100% and specificity from 68% to 97% 1, 3
• The double contour sign (hyperechoic irregular enhancement over superficial margin of hyaline cartilage) has pooled sensitivity of 74% and specificity of 88% 1, 3
• Additional ultrasound features include tophi and hyperechoic aggregates within joint space or synovium 3
• When characteristic ultrasound features are identified, synovial fluid analysis is not needed to confirm gout diagnosis per EULAR guidelines 3

Important limitation: Sensitivity is significantly lower (as low as 37%) in patients with recent-onset acute gout due to lower crystal burden. 3

Dual-Energy CT (DECT)

• DECT sensitivity ranges from 85% to 100% and specificity from 83% to 92% for detecting MSU crystal deposition 2, 1
• Less sensitive in patients with shorter history of flares compared to longer disease duration 2
• All false-negative results in one study occurred in patients with recent-onset acute gout 2
• False-positive results may occur in patients with advanced osteoarthritis of the knee 2

Plain Radiography

• Limited value for diagnosing acute gout flares 1
• Useful for identifying chronic changes and ruling out other conditions 1
• No studies assessed sole use of plain radiography for gout diagnosis 2

Essential Comorbidity Assessment

Systematically evaluate for associated comorbidities including obesity, renal impairment, hypertension, ischemic heart disease, heart failure, diabetes, and dyslipidemia. 1

Risk Factor Evaluation

• Chronic kidney disease 1
• Overweight/obesity 1
• Medications: diuretics, low-dose aspirin, cyclosporine, tacrolimus 1
• Alcohol consumption (especially beer) 1
• Diet high in meat and shellfish 1
• Non-diet sodas and high-fructose corn syrup consumption 1

Diagnostic Algorithm Summary

1. First-line approach: Attempt synovial fluid aspiration with MSU crystal identification if technically feasible and safe 1
2. If aspiration not feasible or unsuccessful: Apply 2015 ACR/EULAR Classification Criteria scoring system incorporating clinical features, serum uric acid, and imaging findings 2
3. Consider ultrasound as preferred imaging modality if available, looking specifically for double contour sign 3
4. If septic arthritis cannot be excluded clinically: Joint aspiration with Gram stain and culture is mandatory regardless of gout suspicion 2, 1
5. DECT may be considered in patients with longer disease duration when diagnosis remains uncertain, but has limited sensitivity in early disease 2