Microalbuminuria and renal morphology in the evaluation of subclinical lupus nephritis.

AIM AND METHOD: In an attempt to evaluate subclinical lupus nephropathy, we analyzed the clinical characteristics, determined the albumin excretion rate (AER) by radioimmunoassay and performed renal biopsy in 30 patients with systemic lupus erythematosus (SLE) who had no clinical signs of renal involvement (no urinary sediment abnormalities, absence of proteinuria, serum creatinine <1.3 mg/dl). All biopsies were classified according to a modified classification proposed by the WHO. RESULTS: Fifteen cases (50%) had mesangial glomerulonephritis (MGN) type IIb, 12 had MGN type IIa and 3 patients showed no changes on light microscopy (LM) or on immunofluorescence (IF) (type I). Anti-IgM-fluorescent deposits were found in 83% of the renal biopsies, being associated with less heavily stained deposits of IgG, IgA and C3. Patients with MGN type IIb showed lower mean age when compared to those of MGN type IIa (26.04 years vs. 36.3 years) (p<0.029); those patients also presented disease duration of 4.8 years and their mean AER was 39.9 microg/min. Six of the patients (6 of 15, 40%) showed positive anti-dsDNA antibodies, in contrast to patients with MGN type IIa who did not show positive anti-dsDNA antibodies (p<0.002). The group with abnormal AER presented lower mean age (p<0.029) and lower C3 levels (p<0.0098) when compared to the group with normal AER. CONCLUSION: The results suggest the high prevalence of MGN type IIb and IgM deposits on IF, despite the paucity of clinical and laboratory data on these patients. Furthermore, there is an association between MGN type IIb and positive anti-dsDNA antibodies and a relationship between abnormal AER and low C3 levels. The level of AER could not determine the presence or absence of renal disease on LM or IF in this population.