How to Diagnose Gout: Exams and Analyses

Gout diagnosis requires a rigorous medical approach combining clinical exams and biological analyses. According to Health Insurance, gout affects approximately 600,000 people in France, with prevalence constantly increasing. This inflammatory condition, caused by the accumulation of sodium urate crystals in the joints, can be diagnosed with precision thanks to several complementary exams.

Early and accurate diagnosis allows for rapid implementation of appropriate treatment and prevents long-term joint complications. High Health Authority recommendations emphasize the importance of a structured diagnostic approach to distinguish gout from other inflammatory arthropathies.

This article details the various available exams, their indications, their limitations and the interpretation of results to establish reliable gout diagnosis.

Clinical Exam: First Step in Diagnosis

Thorough Medical History

Medical history forms the basis of gout diagnosis. The physician looks for:

• Family history: gout has a genetic component in 20% of cases
• Risk factors: obesity, high blood pressure, diabetes, kidney failure
• Eating habits: alcohol consumption, foods rich in purines
• Medications: diuretics, low-dose aspirin, cyclosporine
• Comorbidities: metabolic syndrome, cardiovascular diseases

Physical Exam of the Joint

Physical examination helps identify characteristic signs:

• Acute monoarthritis: involvement of a single joint initially
• Typical location: big toe (podagra) in 50% of first episodes
• Inflammatory signs: intense pain, redness, heat, swelling
• Tophi: visible urate deposits under the skin (advanced stages)

The typical gout attack begins suddenly, often at night, with maximum pain in 6 to 12 hours.

To effectively manage an acute attack, consult our guide to emergency measures during a gout attack.

Biological Analyses: Uric Acid Testing

Serum Uric Acid: Reference Exam

Serum uric acid testing (uricemia) is the main biological exam:

• Normal values:
  • Men: < 70 mg/L (420 μmol/L)
  • Women: < 60 mg/L (360 μmol/L)
• Hyperuricemia: > 70 mg/L in men, > 60 mg/L in women
• Crystallization threshold: risk of crystal formation > 80 mg/L

Timing of Sample Collection

The timing of testing significantly influences results:

• During attack: uric acid can be normal or decreased (30% of cases)
• After attack: ideal sampling 4-6 weeks after the attack
• Sampling conditions: patient fasting, avoid physical exertion

24-Hour Urine Uric Acid Testing

24-hour uricosurial helps guide treatment:

• Normal values: 300-700 mg/24h under normal diet
• Overproduction: > 700 mg/24h (enzymatic deficiency, cell breakdown)
• Underelimination: < 300 mg/24h (kidney failure, genetic)

According to a study published on PubMed in 2023, uricosurial analysis allows optimization of therapeutic choice between uric acid-lowering drugs.

Joint Aspiration and Synovial Fluid Analysis

Technique and Indications

Joint aspiration remains the reference exam for confirmed diagnosis:

• Sterile technique: performed by an experienced physician
• Indications: first episode, diagnostic doubt, suspected septic arthritis
• Contraindications: skin infection in the area, bleeding disorders

Synovial Fluid Analysis

Several parameters are analyzed:

Parameter	Normal Values	Gout
Appearance	Transparent	Turbid, purulent
Viscosity	High	Decreased
White blood cells	< 200/mm³	10,000-50,000/mm³
Neutrophils	< 25%	> 90%
Crystals	Absent	Sodium urate

Identification of Urate Crystals

Polarized light examination allows specific identification:

• Shape: needle-shaped crystals (acicular)
• Birefringence: strongly negative
• Location: intracellular (neutrophils) and extracellular
• Color: yellow when parallel to compensator axis

The presence of sodium urate crystals in synovial fluid confirms gout diagnosis with 100% specificity.

Medical Imaging Exams

Standard X-rays

X-rays provide information about disease progression:

• Acute phase: often normal or soft tissue edema
• Chronic phase: erosions resembling nail marks