Hyperuricemia - Gout

Diagnosis

Indications for Testing

  • Swollen, erythematous joint(s)

Criteria for Diagnosis

  • Diagnosis based on criteria from the American College of Rheumatology (Wallace, 1977); however, recent guidelines from the European League Against Rheumatism (EULAR) (Zhang, 2006) may be more applicable

Laboratory Testing

  • Synovial fluid examination
    • Essential if main differential diagnosis is between gout and septic joint – otherwise not used very often
    • Cell count – predominance of polymorphonuclear cells
      • Absolute WBC cell count usually <50,000
    • Crystals – presence of uric acid crystals in fluid as viewed by polarized light microscopy is diagnostic
    • Gram stain and culture to rule out septic arthritis
  • Serum uric acid – may be elevated; lack of elevation does not rule out gout
    • Elevated in only 50% of patients during an acute attack
    • Best time to measure may be ≥2 weeks after an acute attack
    • If normal value detected during acute attack, repeat when joint normalizes
  • CBC – modest leukocytosis may be present
    • Significant leukocytosis suggests septic joint
  • BUN and creatinine – to evaluate renal function
    • Drugs used to treat acute and chronic gout may affect renal function

Imaging Studies

  •  Acute gout – not useful
  • Chronic gout – may demonstrate tophi; erosive joint disease

Differential Diagnosis

  • Calcium pyrophosphate dihydrate disease (pseudogout)
  • Reactive arthritis (eg, Campylobacter jejuni)
  • Septic arthritis
  • Cellulitis
  • Osteoarthritis
  • Rheumatoid arthritis
  • Internal ligament derangement
  • Hemarthropathy
  • Traumatic arthritis

Monitoring

  • Therapeutic goals are usually based on initial uric acid levels with attempts to normalize (<6 mg/dL)

Clinical Background

Gout is a type of arthritis caused by hyperuricemia leading to deposits of monosodium urate crystals in tissues and joints.

Epidemiology

  • Prevalence – >8 million Americans yearly (Hainer, 2014)
  • Age – unusual <30 years; peaks at 12% >80 years
  • Sex – M>F; 4-9:1

Risk Factors

  • Obesity (BMI ≥30 kg/m2)
  • Diuretic therapy (loop diuretics have highest risk)
  • Diet high in fructose corn syrup (eg, sweetened beverages)
  • High purine diet (red mean, wild game, or organ meats)
    • Nuts, oats, asparagus, legumes are high in purine but don’t seem to increase risk
  • Alcohol consumption  (particularly beer)
  • Male sex (female sex hormones increase uric acid excretion)
  • Common acute attack triggers in patients with preestablished gout
    • Trauma
    • Surgery
    • Psoriasis exacerbations
    • Diuresis
    • Starting or stopping allopurinol
    • Infections

Pathophysiology

  • Uric acid – final byproduct of purine metabolism; poorly soluble
  • Hyperuricemia – often caused by altered purine metabolism, leads to increased levels of uratic acid
    • Decreased excretion, increased production, or a combination of factors may be involved as etiology of hyperuricemia
    • When solubility limits are exceeded, monosodium urate crystals precipitate in joints, kidneys, and soft tissues
      • Crystal deposition triggers immune activation with release of inflammatory cytokines and neutrophils
      • Tophi may form at joint space – monosodium urate crystals in a matrix of lipids, protein, and mucopolysaccharides

Clinical Presentation

  • Typically a clinical diagnosis
  • Monoarticular arthritis
    • More common in lower extremities – typical joints include first metatarsophalangeal, midfoot, ankle
  • Pain, erythema, and swelling of joint – abrupt onset; commonly takes <24 hours to go from asymptomatic to maximum pain
  • May cause fever, leukocytosis, and/or cellulitis over joint
  • Chronic gout
    • Tophi – subcutaneous nodules
    • Joint erosion and destruction
    • Sepsis in joints – knee and olecranon bursa most common
    • Increased susceptibility

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Cell Count, Body Fluid 0095019
Method: Cell Count/Differential

Aid in differentiation of gout from septic arthritis

   
Gram Stain 0060101
Method: Stain/Microscopy

Aid in differentiation of gout from septic arthritis

   
Body Fluid Culture and Gram Stain 0060108
Method: Stain/Culture/Identification

Aid in differentiation of gout from septic arthritis

Anaerobe culture is NOT included with this order

 
Uric Acid, Serum or Plasma 0020026
Method: Quantitative Spectrophotometry

Aids in diagnosis of gout

Lack of elevation does not rule out gout (may also be normal during acute attack)

If normal when performed during acute attack, repeat testing when joint normalizes

CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

Aid in differentiation of gout from septic arthritis

   
Additional Tests Available
 
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Urea Nitrogen, Serum or Plasma 0020023
Method: Quantitative Spectrophotometry

Assess renal function in gout

Creatinine, Serum or Plasma 0020025
Method: Quantitative Enzymatic

Assess renal function in gout

Uric Acid, Urine 0020481
Method: Quantitative Spectrophotometry
Uric Acid, Body Fluid 0020513
Method: Quantitative Spectrophotometry