BACKGROUND: Systemic lupus erythematosus (SLE) leads to renal lesions, which may be clinically silent in patients with little or no proteinuria. Early detection of these lesions may improve prognosis, but early markers are controversial. This study aimed to determine renal marker proteins associated with renal lesion severity in patients with lupus nephropathy (LN) and little or no proteinuria.

MATERIAL AND METHODS: Patients with LN and little or no proteinuria (<0.5 g/24 hours) (n=187) that underwent kidney biopsy were grouped according to: low severity (Class I or II; n=116) versus high severity (Class III, IV, or V; n=71). Disease status was determined according to the SLE disease activity index (SLEDAI). Renal marker proteins (serum β2-macroglobulin, urinary β2-macroglobulin, albumin, IgG, and α1-macroglobulin) were measured using radioimmunoassay.

RESULTS: Compared with the low severity group, patients in the high severity group had higher urinary albumin (11.60±8.94 versus 7.08±10.07 µg/mL, p=0.008) and urinary IgG (13.21±9.35 versus 8.74±8.90 µg/mL, p=0.007) levels. Multivariate conditional logistic regression analysis showed that urinary albumin (odds ratio (OR)=1.417, 95% confidence interval (95% CI): 1.145–1.895, p=0.001) and SLEDAI (OR=2.004, 95% CI: 1.264–3.178, p=0.003) were independently associated with severe renal lesions in these patients. Using an optimal cutoff point of urinary albumin of 7.53 µg/mL resulted in 67% sensitivity and 82% specificity for the detection of high severity renal lesions.

CONCLUSIONS: Urinary albumin levels and SLEDAI were independently associated with histological severity of renal lesions in patients with LN and little or no proteinuria. These parameters could be used to help select patients for renal biopsy.

Keywords: lupus nephritis, Proteinuria