Is serum uric acid a predictor of long-term renal outcome in lupus nephritis?

Background/objective: Recent studies observed an association between increased serum uric acid (SUA) levels and renal damage in lupus. However, the predictive value of UA for the development of long-term renal dysfunction in lupus nephritis (LN) is still unknown. The aim of this study was to evaluate if SUA may be a predictor of long-term renal outcome in LN.

Methods: Eighty biopsy-proven LN patients > 7 years of follow-up were selected. SUA levels were measured in sera stored at - 70 °C. All patients had serum stored from LN baseline, and 32 also had stored serum from 6 and 12 months after LN. Renal outcome was addressed after 7 years of follow-up to determine if SUA could be a predictor of long-term renal outcome. A good long-term renal outcome in 7 years was defined as a creatinine clearance (CrCl) ≥ 90.0 mL/min/1.73 m², and poor if CrCl < 90 mL/min/1.73 m². Patients were divided in two groups according to the renal outcome to assess whether SUA levels at different time points of follow-up could differentiate such groups. An ROC curve was plotted to assess accuracy.

Results: SUA levels at baseline and 6 months were not able to differentiate good from poor long-term renal outcomes in LN (respectively p = 0.37, p = 0.28), but at 12 months (p = 0.02), they could clearly differentiate the two groups. ROC curve (12 months) accuracy was 0.76. SUA cutoff was 6.05 mg/dL (sensitivity = 0.67, specificity = 0.89, positive predictive value = 0.85, negative predictive value = 0.73).

Conclusion: SUA levels < 6.05 mg/dL at 12 months of follow-up is a predictor of good long-term renal outcome in lupus nephritis.

Key points: • Previous studies reported an association between increased serum uric acid level and short-term renal damage in lupus patients. • The predictive value of serum uric acid for the development of long-term renal dysfunction in lupus nephritis was never assessed. • At 12 months of follow-up serum uric acid clearly differentiated good from poor long-term renal outcome in lupus nephritis. • SUA level < 6.05 mg/dL at 12 months of follow-up was a predictor of good long-term renal outcome in lupus nephritis.