Glomerular filtration rate and urinary albumin excretion rate in systemic lupus erythematosus

Our objective was to more precisely determine glomerular function in patients with systemic lupus erythematosus (SLE), without abnormalities in renal function, as determined by standard clinical laboratory tests. Our long-term goal is to identify patients during clinical quiescence who may be at high risk of developing progression to renal failure from lupus nephritis. We studied three groups of subjects: 8 patients with SLE and a history of nephritis, now in remission; 25 patients with SLE, without clinical evidence of nephritis, now or in the past; and 5 healthy women (normal controls). At the time of study, urinalysis, serum creatinine and 24-hour urine total protein excretion were within the normal range in each subject. We measured glomerular filtration rate (GFR) by ¹²⁵I-iothalamate clearance. and albumin excretion rate (AER) by enzyme-linked immunosorbent assay (ELISA) in timed urine specimens. In addition, we compared 4-hour AER with 24-hour AER and spot urine albumin/creatinine ratio (A/C). Among patients with a history of nephritis now in remission, mean GFR was slightly but not significantly lower and mean GFR was elevated (p < 0.03). Among patients with SLE without a history of nephritis, mean GFR was normal, but the variance in GFR was greater than normal (p < 0.005). Seven patients without nephritis (28%) had either hyperfiltration or hypofiltration. Mean AER was normal, but 3 other patients (12%) had elevated AER. There was no correlation of GFR and AER among patients in either group. Correlations (r) of spot urine A/C and 24-hour AER with 4-hour AER were 0.93 (p < 0.001) and 0.88 (p < 0.001), respectively. We conclude that most patients with SLE and a history of nephritis now in remission have persistent abnormalities in glomerular function, and as many as 40% of patients without a history of nephritis also have subtle defects in glomerular function. Whether these abnormalities in glomerular function define a subset of patients at higher risk of developing renal failure, independent of disease activity, requires further study. Spot urine A/C is a valid measure of AER in SLE.