Objective  To explore the role of urinary osteopontin (uOPN) in predicting clinical responses to induction therapy and renal prognosis in adults with lupus nephritis (LN).

Methods  A total of 53 type Ⅲ/Ⅳ LN adults were recruited. At the same time, 24 healthy volunteers visiting our hospital for physical examination in the same period were selected as healthy control group. Levels of uOPN were determined by enzyme-linked immunosorbent assay (ELISA). Renal biopsies were performed at baseline and after induction therapy. According to the criteria of American College of Rheumatology (ACR), they were divided into two groups of clinical response or non-response. Patients with ≥50% improvement in renal activity index scores were selected as histological response group.

Results  Baseline and post-treatment levels of uOPN were significantly higher in LN patients than those in healthy controls 2.33(1.84, 2.83)mg/L, 2.07(1.55, 2.72)mg/L vs 0.94(0.70, 1.46)mg/L(P<0.05). And baseline uOPN in type Ⅳ LN patients were significantly higher than those with type Ⅲ LN 2.39(1.93, 3.07)mg/L vs 1.87(1.57, 2.45)mg/L, P=0.005. As compared with clinical/histological response subgroup, baseline uOPN 3.06(1.92, 3.41)mg/L vs 2.46(2.24, 3.10)mg/L , 3.12(2.03, 3.35)mg/L vs 2.47(2.15, 3.13)mg/L and OPN level post-treatment 3.04(1.56, 3.63)mg/L vs 2.37(1.82, 2.65)mg/L, 3.09(1.76, 3.57)mg/L vs 2.30(1.79, 2.68)mg/L were higher in non-response subgroup (P<0.05). Furthermore, only clinical/histological response subgroup demonstrated a lower level of OPN 2.37 (1.82, 2.65)mg/L vs 2.46 (2.24, 3.10)mg/L, 2.30(1.79, 2.68)mg/L vs 2.47 (2.15, 3.13)mg/L from baseline post-treatment (P<0.05) while non-response group showed no significant change before and after treatment (P>0.05). Multivariate Logistic regression analysis revealed that baseline uOPN was an independent predictor of histological response to LN induction therapy (P<0.05). ROC curve analysis indicated that the area under the curve (AUC) of baseline uOPN level in predicting histological response to induction therapy was 0.721(95%CI:0.550-0.892) with a specificity of 55.6% and a sensitivity of 81.8% in LN patients.

Conclusions  Reflecting renal activity in adults with type Ⅲ/Ⅳ LN, uOPN may predict histological responses to induction therapy. Elevated level of uOPN post-treatment may reflect the progression of renal injury and worse renal prognosis.