Diagnosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

The diagnosis of gout is based upon the identification of intracellular monosodium urate (MSU) crystals in the synovial fluid aspirate of an affected joint, under polarizing light microscopy. But when this is not possible, a clinical diagnosis can be deduced with the help of classical clinical features, including the history and physical examination, laboratory findings, and various imaging studies.

Diagnosis of acute gout

• While the favored approach is to find MSU crystals in the synovial fluid aspirate of an affected joint, in clinical practice a crystal evaluation is routinely not done.
• When a patient is presenting with classic symptoms of rapid onset (within 24 hours), podagra, swelling, and erythema, supported by the presence of hyperuricemia, a clinical diagnosis of gout can easily be concluded.
• When an arthrocentesis is done, synovial fluid should be examined readily under routine light and polarizing light microscopy and looked for negatively birefringent needle-shaped MSU crystals.
• In addition, testing for cell counts with differential, gram staining and culture should also be done on the aspirate.
• The sensitivity of this technique in demonstrating negatively birefringent intra- and extracellular crystals in patients with gout flares is at least 85 percent, and the specificity for gout is 100 percent. . The sensitivity of can be further improved by examination of the sediment in a centrifuged specimen.

Accuracy of diagnostic criteria for gout among patients who had synovial fluid analysis

	Criteria	Sensitivity	Specificity
ARA (ACR)	6 of 12 criteria	70%	79%
Rome	2 of 4 criteria: • Painful joint swelling, abrupt onset, Clearing in 1-2 weeks initially • Serum uric acid: >7 in males; >6 in females • Presence of tophi • Urate crystals in synovial fluid or tissues	70%	83%
New York	2 of 5 criteria: • 2 attacks of painful limb joint swelling • Abrupt onset and remission in 1—2 weeks initially • First MTP attack • Presence of a tophus • Response to colchicine-major reduction in inflammation within 48 h	67%	89%

Several sets of diagnostic criteria exit (see table).

The serum uric acid level during an attack of gout

	Sensitivity	Specificity
> 5.88 mg/dl	95%	53%
≥ 6 mg/dl	86%	?
≥ 8 mg/dl	68%	?

A clinical prediction rule (online link) found that the following predicted urate crystals by aspiration:

• Male
• Onset within one day
• Joint redness
• First metatarsaophalangeal joint
• Previous arthritis attack per patient
• History of hypertension or 1 or more cardiovascular diseases
• Serum uric acid level > 5.88 mg/dl

However, among patients with high scores, 20% did not have crystals. Only one of 381 patients had bacterial arthritis.

 Diagnosis of intercritical and tophaceous gout

• In patients where a diagnosis of gout wasn’t ascertained during an acute flare, a synovial fluid analysis identifying urate crystals from the previously affected joints would allow a late establishment of the disease.
• Urate crystals are present in synovial fluid of all untreated gouty patients and in approximately 70 percent of those under urate-lowering therapy. 8624633 10577299 444319
• For tophaceous gout, demonstration of urate crystals in aspirates of tophi provides an easy way to confirm the diagnosis 10834006

 Clinical diagnosis “rule” for acute gout

• In patients with acute gout where a diagnosis couldn’t be confirmed due to a negative synovial fluid analysis for MSU crystals, a clinical diagnostic approach can be implemented. 20625017
• This approach utilizes a set of clinical parameters with a scoring value. The parameters are derived from history, clinical presentation, and the laboratory findings. 25231179
• This approach has been shown to improve the accuracy of diagnosis without joint fluid analysis of a gout flare in primary care practice settings 20625017
• The model uses seven variables to calculate a total score to distinguish three levels of risk for gout. These are:
  1. Male sex (2 points)
  2. Previous patient-reported arthritis flare (2 points)
  3. Onset within one day (0.5 points)
  4. Joint redness (1 point)
  5. First metatarsal phalangeal joint involvement (2.5 points)
  6. Hypertension or at least one cardiovascular disease (1.5 points)
  7. Serum urate level greater than 5.88 mg/dL (3.5 points)

• Based upon the total score, patients can be identified as having low (≤4 points), intermediate (>4 to <8 points), or high (≥8 points) probability of having acute gout.
• In patients with an intermediate score (>4 but <8 points), a preliminary diagnosis of gout may be made for the purpose of clinical management based upon a prevalent clinical features favoring gout.
• This diagnostic approach is not recommended for patients presenting with oligoarticular and polyarticular arthritis, as it was developed studying patients with monoarthritis seen by family physicians.