A 62-year-old man presents with acute monoarthritis of the right knee. Joint fluid aspiration shows negatively birefringent needle-shaped crystals on polarised light microscopy. Serum uric acid is 5.8 mg/dL (normal). Which statement is most accurate?
- A Serum uric acid can be normal or even low during an acute gout attack due to uricosuric effects of acute inflammation and cortisol release; crystal identification confirms the diagnosis ✓
- B A normal serum uric acid at the time of an acute attack excludes gout
- C Negatively birefringent crystals indicate calcium pyrophosphate deposition, not gout
- D The patient must have a baseline serum uric acid > 7 mg/dL to be diagnosed with gout
Correct answer: A. Serum uric acid can be normal or even low during an acute gout attack due to uricosuric effects of acute inflammation and cortisol release; crystal identification confirms the diagnosis
Explanation
Serum uric acid frequently falls during acute gout attacks due to the uricosuric effects of ACTH and cortisol released in response to inflammation; thus a normal level does not exclude gout. Crystal identification — negatively birefringent needle-shaped monosodium urate crystals — remains the diagnostic gold standard. Calcium pyrophosphate crystals are weakly positively birefringent and rhomboid-shaped.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.