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 chief differential diagnosis is between gout and septic joint
    • Cell count – may see predominantly polymorphonuclear cells; absolute count usually <50,000
    • Crystals – gold standard for diagnosis is presence of uric acid crystals in fluid
    • Gram stain – rule out septic arthritis
    • Culture – rule out septic arthritis
  • Serum uric acid – may be elevated; however, lack of elevation does not rule out gout
    • Elevated in only 50% of those with acute attacks
    • Best time to measure may be 2 weeks after a flare-up
    • If performed during acute attack and normal, repeat when joint normalizes
  • CBC – modest leukocytosis may be present
    • May be helpful in discriminating septic joint from gout if significant leukocytosis is present
  • BUN and creatinine – 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

Differential Diagnosis

Monitoring

  • Therapeutic goals based on initial uric acid levels
    • Attempt to decrease to <6 mg/dL

Clinical Background

Gout is a type of arthritis caused by hyperuricemia (high serum uric acid) leading to deposits of urate crystals in tissues and joints.

Epidemiology

  • Prevalence – 2% in males >30 years and females >50 years
  • Age – unusual <30 years
  • Sex – M>F; 4-9:1

Risk Factors

  • Hyperuricemia
  • Obesity
  • Diuretic therapy
  • High purine diet
  • Alcohol use
  • Common triggers in patients with a history of gout – trauma, surgery, psoriasis exacerbations, diuresis, starting or stopping allopurinol, infections

Pathophysiology

  • Uric acid – final byproduct of purine metabolism; poorly soluble
  • Hyperuricemia (common in gout) – caused by altered purine metabolism leading to increased levels of urate
    • Decreased excretion, increased production, or a combination of factors may be involved
    • When solubility limits exceeded, monosodium urate crystals can deposit in joints, kidneys, and soft tissues

Clinical Presentation

  • Usually involves single joint
    • More common in lower extremities – typical joints include first metatarsophalangeal, midfoot, ankle
  • Pain, erythema, and swelling of joint – abrupt onset; usually takes <24 hours to go from no pain to maximum pain
  • May cause fever, leukocytosis, and/or cellulitis over joint
  • Chronic gout
    • Tophi – nodular mass of urate crystals in soft tissue
    • Joint erosion and destruction
    • More susceptible to septic joints – knee and olecranon bursa common

Treatment

  • Acute therapy – includes nonsteroidal anti-inflammatory drugs (NSAIDS), steroids, and colchicine
  • Chronic therapy – includes urate-lowering drugs, dietary adjustment, adequate fluid intake

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

Use to aid in differentiating gout from septic arthritis

   
Gram Stain 0060101
Method: Stain/Microscopy

Rule out septic arthritis

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

Rule out septic arthritis

   
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 performed during acute attack and normal, repeat when joint normalizes

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

May aid in differentiating gout from septic joint if significant leukocytosis is present

   
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

   
Additional Tests Available
 
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Uric Acid, Urine 0020481
Method: Quantitative Spectrophotometry
Uric Acid, Body Fluid 0020513
Method: Quantitative Spectrophotometry