Standard Operating Procedure: Serum Uric Acid

1. Purpose and Scope

To measure serum uric acid (urate) concentration for the diagnosis and monitoring of hyperuricemia, gout, nephrolithiasis, and tumor lysis risk, and to guide urate-lowering therapy.

2. Specimen Requirements

• Type: Serum (morning fasting preferred; uric acid varies little with food but fasting improves comparison with reference data).
• Volume: Minimum 1 mL.
• Stability: Stable up to 48 hours refrigerated; avoid prolonged storage at room temperature.
• Rejection: Hemolyzed samples are acceptable for uric acid but should be flagged; grossly lipemic samples should be ultracentrifuged before analysis.
• Note: Thiazide diuretics and loop diuretics raise serum urate; these medications should be recorded for interpretive purposes.

3. Safety and Precautions

• Standard PPE. All samples are potentially infectious.
• Dispose of waste in biohazard containers.

4. Equipment and Reagents

• Automated chemistry analyzer (spectrophotometric).
• Uricase-peroxidase reagent kit (Tinder/Trinder chromogen) or uricase end-point method.
• Two levels of quality control material.

5. Step-by-Step Procedure

1. Centrifuge the clotted specimen at 3000-3500 rpm for 10 minutes.
2. Load serum onto the analyzer per instrument instructions.
3. Run two levels of quality control before patient samples.
4. Verify calibration linearity within the measuring range; dilute and re-run results above the upper linearity limit.
5. Release results after QC acceptance.

6. Quality Control

• Run 2 levels of control daily for each assay.
• Participate in an external quality assessment (EQA) program.
• Verify control values fall within acceptable target ranges before patient reporting.

7. Decision limits

• Gout treatment target: With urate-lowering therapy, it is generally recommended to treat to a serum urate below 6.0 mg/dL (360 µmol/L), and below 5.0 mg/dL (300 µmol/L) in patients with tophi, using clinical judgement and applicable society guidance (e.g. ACR 2020).
• Acute gout: Serum urate may be normal (or even low) during an acute flare because urate redistributes; 'treatment to target' does not apply to the immediate flare period.
• Tumor lysis risk: Hyperuricemia in the setting of cancer chemotherapy should prompt monitoring for tumor lysis syndrome; thresholds are part of oncologic protocols rather than a single laboratory interval.

8. Reporting Results

• Report results with the assay-specific reference range and flag values above the upper reference limit.
• Interpret uric acid in the context of renal function (uric acid accumulates in chronic kidney disease) and relevant medications.
• Note the sex-specific reference intervals (adult male vs adult female) shown in the canonical panel below.