Prospective study of serum and urinary nitrate levels in patients with systemic lupus erythematosus

OBJECTIVE: To study prospectively whether serum and urinary nitrate levels are related to lupus activity. METHODS: Fifty patients with systemic lupus erythematosus (SLE) were studied prospectively for 2 yr. Every 4 months, the SLE Disease Activity Index (SLEDAI) was administered to the patients, and blood and 24 h urine samples were obtained; 88 healthy controls were also studied. Nitrate levels were measured by the Greiss method. Statistical analyses were performed using standard parametric and non-parametric tests, and analysis of serial measurements. RESULTS: Twelve patients suffered infections, 12 active nephritis and 17 episodes of non-renal activity. By analysis of serial measurements, serum and urinary nitrate levels did not correlate with SLEDAI. C-Reactive protein (CRP) levels, presence of infection and creatinine clearance weakly influenced nitrate levels. CONCLUSIONS: In SLE, serum and urinary nitrate levels do not parallel lupus activity. Other variables, related or not to SLE, seem to affect these levels.