What is the diagnostic approach for an adult patient with suspected gout?

How to Diagnose Gout

Synovial fluid analysis with polarized light microscopy to identify monosodium urate (MSU) crystals remains the gold standard for diagnosing gout, but when this is not feasible, clinical diagnosis using validated criteria combined with ultrasound imaging provides an accurate alternative approach. 1, 2

Three-Step Diagnostic Algorithm

Step 1: Joint Aspiration and Synovial Fluid Analysis (When Feasible)

Perform arthrocentesis when:

• Septic arthritis cannot be clinically excluded 1, 2
• The clinical presentation is atypical or uncertain 3
• This is the patient's first suspected gout attack 1

What to look for:

• Needle-shaped, negatively birefringent MSU crystals under polarizing microscopy (sensitivity and specificity approaching 100%) 2, 3
• Always perform Gram stain and culture even when crystals are identified, as gout and septic arthritis coexist in 5-10% of cases 4

Key limitation: Joint aspiration is technically difficult in smaller joints and rarely performed in primary care settings where most gout is diagnosed 1, 2

Step 2: Clinical Diagnosis (When Joint Aspiration Not Performed)

Use the ACR/EULAR 2015 classification criteria (score ≥8 diagnostic):

• Sensitivity 92%, specificity 89% with imaging 2
• Sensitivity 85%, specificity 78% without imaging 2

High-value clinical features that strongly suggest gout:

• Podagra (first metatarsophalangeal joint involvement) - most characteristic presentation 2
• Maximum pain intensity reached within 6-24 hours - highly specific for crystal inflammation 2
• Erythema over the affected joint 2
• History of previous similar attacks with complete resolution 2
• Male sex and cardiovascular comorbidities (hypertension, obesity, chronic kidney disease) 1, 2

Important caveat about serum uric acid:

• Hyperuricemia alone has only 53-61% specificity and should NOT be used to diagnose gout 2
• However, normal serum uric acid during an acute flare essentially rules out gout (very low likelihood ratio) 2

Critical pitfall: Clinical algorithms have relatively low specificity, raising the risk of missing septic arthritis, which presents similarly 2

Step 3: Imaging (When Clinical Diagnosis Uncertain and Crystal Identification Not Possible)

Ultrasound is the first-line imaging modality: 2, 3

• "Double contour sign" on cartilage surfaces: sensitivity 74%, specificity 88% 2, 3
• Always scan the first metatarsophalangeal joint bilaterally, even if asymptomatic, as this is the most common site for MSU deposition 1, 2
• Performs better in disease duration >2 years (63% sensitivity) versus <2 years (50% sensitivity) 2
• Can also assess inflammation using Doppler mode 1

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

• Sensitivity 85-100%, specificity 83-92% for detecting MSU crystal deposits 2, 3
• Most accurate in patients with disease duration >2 years 3
• Consider when ultrasound is inconclusive or unavailable 2
• More expensive, involves radiation exposure, and less sensitive in early disease 1, 2

Plain radiography has limited value:

• Cannot detect MSU crystals or acute inflammation 2
• Only useful for identifying chronic structural damage in long-standing gout 2

When imaging findings are definitive (double contour sign on ultrasound or MSU deposits on DECT), synovial fluid analysis is not needed to confirm diagnosis 2

Systematic Assessment After Diagnosis

Screen for modifiable risk factors: 1

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

Screen for associated comorbidities: 1

• Renal impairment
• Hypertension
• Ischemic heart disease and heart failure
• Diabetes and dyslipidemia

Common Pitfalls to Avoid

• Do not diagnose gout based on hyperuricemia alone - specificity is too low 2
• Do not skip Gram stain and culture when crystals are found - coexistent septic arthritis occurs in 5-10% 4
• Do not rely solely on clinical diagnosis when septic arthritis cannot be excluded - joint aspiration is mandatory 2
• Do not use ultrasound as the sole diagnostic test in early disease (<2 years) - sensitivity drops to 50% 2
• Do not assume imaging abnormalities always correlate with symptoms - 15-25% of people with asymptomatic hyperuricemia have asymptomatic MSU deposits 2