Insulin-like growth factor binding protein-2 as a novel biomarker for disease activity and renal pathology changes in lupus nephritis

Lupus nephritis (LN) is one of the most serious manifestations of systemic lupus erythematosus. Invasive renal biopsy remains the gold standard for the diagnosis and management of LN. The objective of this study is to validate serum insulin-like growth factor binding protein-2 (IGFBP-2) as a novel biomarker for clinical disease and renal pathology in LN. Eighty-five biopsy-proven lupus nephritis patients, 18 chronic kidney disease (CKD) patients and 20 healthy controls were recruited for enzyme-linked immunosorbent assay (ELISA) testing of serum IGFBP-2 levels. Compared to CKD patients of origins other than lupus or healthy controls, serum IGFBP-2 levels were elevated significantly in LN patients. Serum IGFBP-2 was able to discriminate LN patients from the other two groups of patients [area under the curve (AUC)=0·65, 95% confidence interval (CI)=0·52-0·78; P = 0·043 for LN versus CKD; 0·97, 95% CI=0·93-1·00; P < 0·0001 for LN versus healthy controls]. Serum IGFBP-2 was a potential indicator of both global disease activity and renal disease activity in LN patients, correlated with serum creatinine levels (r=0·658, P<0·001, n=85) and urine protein-to-creatinine levels (r=0·397, P<0·001, n=85). More importantly, in 19 concurrent patient samples, serum IGFBP-2 correlated with the chronicity index of renal pathology (r=0·576, P=0·01, n=19) but not renal pathological classification. In conclusion, serum IGFBP-2 is a promising biomarker for lupus nephritis, reflective of disease activity and chronicity changes in renal pathology.