Uses of Uric Acid and Urate in Clinical Medicine
Uric acid and urate primarily serve as diagnostic and monitoring markers for gout management, with their measurement being essential for diagnosis, treatment decisions, and monitoring therapeutic efficacy.
Diagnostic Uses
Serum uric acid (SUA) measurement helps identify hyperuricemia, a key risk factor for gout, though hyperuricemia alone has limited diagnostic value since some individuals may develop gout without raised SUA or may have normal SUA during an acute attack 1
SUA levels can be used to assess the risk of gout progression, as higher urate levels correlate with increased risk of acute gout flares (odds ratio 1.35) 1
Renal uric acid excretion determination is recommended in selected gout patients, especially those with family history of young-onset gout (before age 25) or renal calculi, to identify overproducers versus underexcreters of uric acid 1
Therapeutic Target
SUA serves as the primary therapeutic target in gout management, with treatment aimed at maintaining levels below the saturation point for monosodium urate (360 μmol/L or 6 mg/dL) to promote crystal dissolution and prevent crystal formation 1, 2
For patients with tophi, a more aggressive target of below 300 μmol/L (5 mg/dL) may be appropriate to accelerate crystal dissolution 3
Monitoring SUA levels is essential to assess the efficacy of urate-lowering therapy and guide dose adjustments of medications like allopurinol 2, 4
Pharmacological Considerations
Allopurinol and other xanthine oxidase inhibitors reduce both serum and urinary uric acid levels by inhibiting the formation of uric acid, unlike uricosuric agents which lower SUA by increasing urinary excretion 5
Probenecid and other uricosuric agents work by inhibiting the tubular reabsorption of urate, thus increasing urinary excretion of uric acid and decreasing serum urate levels 6
The combination of allopurinol with uricosuric agents may be useful in some patients to achieve minimum serum uric acid levels, provided the total urinary uric acid load does not exceed the patient's renal function capacity 5
Monitoring Disease Activity
Regular monitoring of SUA levels (every 6 months) is recommended for patients with gout to ensure continued maintenance below the target of 360 μmol/L 2
SUA levels correlate with gout disease activity - patients with levels less than 357 μmol/L (<6.0 mg/dL) have approximately 5% risk for acute gout attacks, whereas those with levels at or above 357 μmol/L have risks of about 10-15% 1
Potential Non-Articular Impacts
Monitoring SUA may help assess risk for kidney disease, as retrospective data shows patients with gout and high versus low serum urate levels had about a 2-fold difference in new diagnoses of kidney disease (9% vs. 5% at year 3) 1
Uric acid and urate monitoring is important in patients with urolithiasis, as xanthine crystalluria can occur in rare cases, particularly in patients with excessive uric acid production 5
Common Pitfalls in Uric Acid Interpretation
Relying solely on SUA for gout diagnosis is problematic as levels may be normal during acute attacks due to increased renal excretion 1
Discontinuing urate-lowering therapy after achieving symptom control based on normalized SUA is a significant error, as this leads to recurrence of gout flares in approximately 87% of patients within 5 years 2, 4
Underestimating the need for lifelong monitoring of SUA based on temporary symptomatic improvement can lead to suboptimal management 3