Prognostic value of urinary interleukin 6 in patients with IgA nephropathy: an 8-year follow-up study

We evaluated the significance of urinary IL-6 levels in the prediction of long-term renal outcome in patients with IgA nephropathy (IgAN). Fifty-nine patients with biopsy-proven IgAN were enrolled in this study. All patients had a creatinine clearance (Ccr) greater than 80 ml/min and normal serum creatinine concentration (Scr) on enrollment and were followed for 8.07 +/- 1.72 years. Twenty- four-hour urine samples were obtained and urinary IL-6 was measured by ELISA. Fifteen patients exhibited a worsening of renal function (progressor). Renal function of the remaining 44 patients was stable during follow-up (non-progressor). The urinary IL-6 levels of progressors on enrollment were significantly higher than those of non-progressors (3.8 +/- 3.8 and 1.8 +/- 1.5 ng/day, respectively, p = 0.0138). We calculated the risk ratio for the progression to renal failure. Patients with a urinary IL-6 level greater than 2.5 ng/day at diagnosis had a 7.8-fold higher risk for the progression of the disease (95% CI 1.31-46.47, p = 0.024) compared with those whose urinary IL-6 level was less than 1.0 ng/day. In conclusion, urinary IL-6 levels could be used as a predictor of long-term renal outcome in patients with IgAN. Patients with a urinary IL-6 level greater than 2.5 ng/day at diagnosis may have a worse prognosis.