How different urinary albumin excretion rates can predict progression to nephropathy and the effect of treatment in hypertensive diabetics

Abstract

Hypothesis The efficacy of a treatment in a clinical trial depends in part on where the cut-off point is placed for the test result used to select patients for the trial, and this applies to irbesartan in the Irbesartan Microalbuminuria II (IRMA II) trial for preventing nephropathy. Patients and methods Patients in the IRMA II trial were stratified into different pre-treatment albumin excretion rate (AER) ranges to compare the proportion of patients starting in these different ranges (i) that progressed to develop nephropathy within 24 months and (ii) whose AER was over 40 µg/minute at three months. Results The proportion of patients with pre-treatment AER values between 20 and 40 µg/minute progressing to develop nephropathy was 1.25% in the placebo group and 0.78% in the irbesartan group, while for pre-treatment AER values between 41 and 200 µg/minute, 24.4% and 11.2% develop nephropathy respectively in the placebo and irbesartan groups. In patients with a pre-treatment AER of 20 to 30 µg/minute, 32.5% and 13.6% respectively in the placebo and irbesartan groups had a value exceeding 40 µg/minute at three months. Conclusions The data demonstrate that irbesartan is effective in reducing the onset of nephropathy within two years when the pre-treatment AER is above 40 µg/minute, but if the AER is below this level it progresses unusually to nephropathy within two years. Irbesartan also slows progression of AER to over 40 µg/minute for patients with pre-treatment AER values at or above 20 µg/minute and these patients should be treated.