Serum and urine nitrite and citrulline levels among patients with systemiclupus erythematosus: A possible addition to activity parameters?

Nitric oxide (NO) plays a significant role in the inflammatory process and has been implicated in several autoimmune disorders. This study was carried out prospectively to estimate the levels of nitrite and citrulline in the serum and urine, as surrogate markers of NO production, among patients with systemic lupus erythematosus (SLE). Forty-seven patients and 44 age-and se x-matched, healthy volunteers were studied. Nitrite and citrulline were mea sured in serum and urine by spectrophotometry. Median serum nitrite and cit rulline levels and urine citrulline levels were higher among patients as co mpared with controls (p < 0.05). Patients with skin involvement stood out a nd had higher median serum and urine citrulline levels (p < 0.05). Disease activity correlated with steroid dosage, serum nitrite levels, and serum an d urine citrulline levels (p < 0.05). Steroid dosage correlated with serum citrulline level (P < 0.05). Serum and urine citrulline levels correlated w ith each other (p < 0.01). In the subset of 13 individuals with renal invol vement, serum and urine citrulline levels correlated with each other (p < 0 .01) as did urine nitrite and citrulline levels (p < 0.05). NO production is increased among patients with SLE, and this increase corre lates with disease activity and dosage of steroids used. The addition of a urine test to measure NO production as a marker of disease activity using s imple spectrophotometry can be a valuable adjunct to other tests, can obvia te the need for drawing a blood sample for this purpose, and can be repeate d as often as necessary.