Fractional excretion of high- and low-molecular weight proteins and outcome in primary focal segmental glomerulosclerosis.

Abstract

AIMS: Predicting prognosis in patients with a nephrotic syndrome due to primary FSGS remains difficult. Recently, it was suggested that the fractional excretion (FE) of IgG (threshold 0.14%) predicts remission, progression to renal failure and response to therapy in FSGS. In the present study, we evaluated the usefulness of FE IgG to guide treatment of patients with primary FSGS in clinical practice. METHODS: From 1995 onward, FE of IgG was measured in 32 adult patients with biopsy-proven primary FSGS. In addition, we quantified 24-hour proteinuria, selectivity index (SI) and FE of albumin, IgG, transferrin and beta2-microglobulin (beta2m). We evaluated outcome in patients with FE IgG above and below 0.14%. Receiver-operating curves were used to determine the best cut-off values for other urinary proteins in predicting remission, response to therapy and renal survival. RESULTS: Mean age was 45 +/- 17 years, serum creatinine 128 +/- 58 micromol/l, proteinuria 10.3 +/- 4.7 g/day and serum albumin 18 +/- 7 g/l. Twenty-three patients received immunosuppressive therapy (9 prednisone and 14 prednisone and cyclophosphamide). After a median follow-up of 58.3 (4.9-127.6) months, 17 patients were in remission (10 complete, 7 partial), 6 patients still had a nephrotic syndrome, renal failure developed in 6 patients, and 3 patients had died. Remission rate was similar in patients with FE IgG less or greater than 0.14%. More patients with FE IgG > 0.14% had received immunosuppressive therapy. Additional analysis revealed that the predictive value of FE of albumin, transferrin and beta2m was low. In untreated patients, FE beta2m < 1% predicted a better renal survival. CONCLUSIONS: Our data indicate that a FE IgG > 0.14% is not invariably associated with a poor outcome in patients with primary FSGS. Therefore, high FE IgG should not lead to therapeutic nihilism. Low FE beta2m predicted a good prognosis without immunosuppressive therapy.