Typical Uric Acid Levels During Gout Flares
Serum uric acid levels during an acute gout flare are often normal or even low—approximately 10-63% of patients with acute gout attacks have serum uric acid levels below 6 mg/dL, making serum uric acid an unreliable diagnostic marker during acute episodes. 1, 2
Why Uric Acid Levels Drop During Flares
Serum uric acid behaves as a negative acute phase reactant during acute inflammation, temporarily decreasing when measured during gout attacks compared to intercritical periods. 1 The proposed mechanisms include:
- Increased renal excretion of uric acid occurs during acute inflammatory episodes 1
- Acute inflammation and stress cause temporary lowering of serum uric acid levels 1
- Studies have documented that 55% of patients with acute gout and normal serum uric acid had increased urinary uric acid excretion 2
Actual Levels Observed During Flares
The evidence shows a wide range of serum uric acid levels during acute attacks:
- Approximately 63.3% of patients with acute gout attacks had normal serum uric acid levels in one clinical study 2
- Roughly 10% of people with gout have serum uric acid levels below 6 mg/dL during flares 1
- Mean serum uric acid during acute gout was 8.4 ± 1.1 mg/dL in one cohort, but this included many patients with elevated levels 3
- Patients may have serum uric acid "even within the normal range" when measured during acute attacks 1
Critical Clinical Implications
The EULAR guidelines explicitly state that serum uric acid levels do not confirm or exclude gout (strength of recommendation: 95% CI 92-99), as many people with hyperuricemia never develop gout, and patients with crystal-proven gout may have normal levels during acute attacks. 1
Common Diagnostic Pitfalls to Avoid:
- Never rule out gout based solely on normal serum uric acid levels, especially during an acute attack 4, 5
- Serum uric acid has limited diagnostic value during acute gout flares and should preferably be measured at distance from a flare 1
- The diagnosis of acute gout should not be excluded in the presence of normal serum uric acid levels if clinical manifestations or positive response to colchicine are suggestive 2
When to Measure Serum Uric Acid
For diagnostic purposes, serum uric acid should be measured during the intercritical period (between attacks) rather than during acute flares, as levels are typically higher when inflammation has resolved. 1
For monitoring treatment efficacy, regular serum uric acid measurements are essential to ensure target levels below 6 mg/dL (360 μmol/L) are maintained, or below 5 mg/dL (300 μmol/L) in severe gout with tophi. 4, 6, 7
Reference Values for Context
While not diagnostic during flares, understanding baseline hyperuricemia thresholds is important:
- Upper limit of normal is approximately 7 mg/dL for men and postmenopausal women, and 6 mg/dL for premenopausal women 7
- Hyperuricemia is defined as serum uric acid >6.8 mg/dL, which is the saturation point for monosodium urate crystal formation 8
- Treatment target is <6 mg/dL to prevent crystal formation and promote dissolution 7, 8, 9