Filtration fraction: an index of renal disease activity in patients with systemic lupus erythematosus.

Renal plasma flow (RPF) and glomerular filtration rate (GFR) were estimated by 125I hippuran and 51Cr EDTA clearances using a single shot technique on two occasions at one-year intervals in 22 patients fulfilling the ARA criteria for systemic lupus erythematosus (SLE). All these patients had histologically proven renal disease. Filtration fraction was a better parameter than proteinuria, urinary sediment or GFR for recognising diffuse proliferative glomerulonephritis with a sensitivity of 61 per cent and a specificity of 88 per cent. After one year all the patients with an initially low filtration fraction (FF) had significantly changed their GFR, which demonstrates that this parameter indicates the presence of an active renal lesion.