What are the steps involved in a gout workup?

Gout Workup

The workup for gout follows a three-step diagnostic approach: first, attempt joint aspiration for monosodium urate (MSU) crystal identification via polarized light microscopy (the gold standard); if not feasible, make a clinical diagnosis based on characteristic features plus hyperuricemia; and if diagnosis remains uncertain, use ultrasound imaging to detect MSU crystal deposition. 1

Step 1: Crystal Identification (Gold Standard)

Perform arthrocentesis and synovial fluid analysis whenever possible, as MSU crystal identification has 100% specificity and 84% sensitivity for diagnosing gout. 2, 3

• Aspirate the affected joint and examine synovial fluid under polarized light microscopy for needle-shaped, negatively birefringent MSU crystals 2
• Always perform Gram stain and culture even when MSU crystals are identified, as gout and septic arthritis can coexist 2, 3
• During intercritical periods, synovial fluid analysis can still detect MSU crystals in approximately 70% of patients with known gout 3
• If septic arthritis cannot be excluded clinically, joint aspiration is mandatory regardless of gout suspicion 2

Step 2: Clinical Diagnosis (When Crystal Identification Not Feasible)

When joint aspiration is not possible or practical, diagnose gout clinically using the ACR/EULAR classification criteria, which have 92% sensitivity and 89% specificity when imaging is included. 2

Key Clinical Features to Assess:

• Monoarticular arthritis affecting the first metatarsophalangeal joint (podagra) 2, 3
• Rapid onset of severe pain reaching maximum intensity within 24 hours 2
• Erythema over the affected joint 2
• History of previous similar attacks 2, 3
• Male gender 2, 3
• Presence of tophi (odds ratio 7.29 for diagnosis) 2
• Resolution of pain by 2 weeks (odds ratio 3.58) 2
• Cardiovascular comorbidities 2

Laboratory Testing:

• Measure serum uric acid (SUA), though hyperuricemia alone is not diagnostic 2, 3
• A cut-off of 6 mg/dL has moderate sensitivity (67%) and specificity (78%) 3
• Note that SUA can be normal or low during acute attacks, so a normal level does not exclude gout 3

Step 3: Imaging (When Diagnosis Remains Uncertain)

Use ultrasound as the preferred imaging modality when crystal identification is not possible and clinical diagnosis is uncertain. 1

Ultrasound Findings:

• Screen affected joints plus both first metatarsophalangeal joints and knees (common sites for MSU deposition) 1
• Look for the "double contour sign" at cartilage surfaces, which has 74% sensitivity and 88% specificity (odds ratio 7.23) 2, 3
• Ultrasound can detect tophi not evident on clinical examination 3
• Sensitivity ranges from 37-100% and specificity from 68-97% for detecting MSU crystal deposition 2
• Ultrasound can facilitate joint aspiration in joints with urate deposits but no clinical effusion 1

Alternative Imaging:

• Dual-Energy CT (DECT) has 85-100% sensitivity and 83-92% specificity but is expensive, involves radiation, and is less sensitive in early disease 2, 3
• Consider DECT only when ultrasound is not feasible or for technically complicated cases (e.g., spinal gout) 1
• Plain radiographs have limited value for acute gout but can identify chronic changes and rule out other conditions 2, 3

Essential Risk Factor Assessment

Once gout is diagnosed, systematically evaluate all modifiable and non-modifiable risk factors for hyperuricemia. 1, 3

Medical Risk Factors to Identify:

• Chronic kidney disease 1, 3
• Medications: diuretics, low-dose aspirin, cyclosporine, tacrolimus 1, 3
• Overweight/obesity 1, 3

Lifestyle Risk Factors:

• Excess alcohol consumption (particularly beer and spirits) 1, 3
• Diet high in meat and shellfish 1, 3
• Non-diet sodas and high-fructose corn syrup consumption 2, 3

Special Testing:

• Measure 24-hour urinary uric acid excretion in patients with family history of young-onset gout, gout onset before age 25, or history of renal calculi 3

Mandatory Comorbidity Screening

Systematically assess for associated comorbidities in all patients with gout, as these have therapeutic implications and affect mortality. 1, 3

Screen for:

• Obesity 1, 3
• Renal impairment 1, 3
• Hypertension 1, 3
• Ischemic heart disease 1, 3
• Heart failure 1, 3
• Diabetes 1, 3
• Dyslipidemia 1, 3

Critical Pitfalls to Avoid

• Do not rely solely on serum uric acid levels for diagnosis—they can be normal during acute attacks 3
• Do not skip Gram stain and culture when MSU crystals are found, as septic arthritis can coexist 2, 3
• Do not use clinical algorithms alone when septic arthritis cannot be excluded—the relatively low specificity increases risk of missed septic joint 2
• Do not order DECT in early disease, as sensitivity is poor in patients with shorter disease duration 2