Sensitive or specific enough for diagnosis???
Additional Information
Gold standard diagnosis remains crystal analysis by polarized light microscopy.
Why can’t we reply on the serum uric acid level?
Elevated uric acid is common and affects >20% of men and 4% of women. The majority of these individuals never develop gout.
This was seen in a large meta-analysis, of asymptomatic patients with hyperuricemia over 15 years of follow-up.
Incidence of gout by baseline serum urate: 1.1% (95% CI 0.9–1.4) for <6 mg/dL, rising in a concentration-dependent way to 49% (95% CI 31–67) for ?10 mg/dL.
As only about half of those with serum urate ?10 mg/dL develop clinically evident gout over 15 years, this implies that prolonged hyperuricemia and additional factors are needed for gout to clinically manifest.
What about during a flare?
A normal value during a flare actually has limited negative predictive value.
Serum urate frequently falls into the "normal" range during an acute attack, due to the uric acid lowering effect of the acute-phase inflammatory response and increased renal excretion
How to use the serum value:
As one component of clinical diagnosis.
When crystal analysis is unavailable, serum urate contributes to validated diagnostic algorithms such as the Janssens diagnostic rule. The rule relies heavily on the uric acid value as it receives the single largest weight in the scoring system.
This clinical prediction rule combines male sex, hx of a prior attack, onset within 1 day, joint redness, first MTP involvement, hypertension/cardiovascular disease, and high serum urate.
A score <4 rules out gout in >97% of patients
https://www.mdcalc.com/calc/2175/acute-gout-diagnosis-rule
Take home: Use serum uric acid level to support (not establish) the diagnosis and to guide therapy. BUT, confirm with joint aspiration and crystal analysis whenever feasible, especially to exclude septic arthritis or pseudo gout.
References
Dalbeth N, Phipps-Green A, Frampton C, Neogi T, Taylor WJ, Merriman TR. Relationship between serum urate concentration and clinically evident incident gout: an individual participant data analysis. Ann Rheum Dis. 2018 Jul;77(7):1048-1052. doi: 10.1136/annrheumdis-2017-212288. Epub 2018 Feb 20.