Individual kidney glomerular filtration rate in the interpretation of non-diagnostic curves on captopril renography

Captopril renography is known to have low sensitivity in the detection of renovascular disease in patients with bilateral renovascular disease and in patients with unilateral renovascular disease with a small kidney. In these groups of patients, we have tried to make the standard captopril renogram more objective by simultaneously estimating the individual kidney glomerular filtration rate (IKGFR). Twenty-five patients (10 bilateral, 15 unilateral) with angiographically proven renal artery stenosis (RAS) were studied. Ten renal units in five hypertensive patients with normal renal arteries were used as controls. A fall of more than 10% in IKGFR post-captorpril was considered a positive result. The sensitivities of renogram and IKGFR in patients with bilateral RAS were 52.9% and 88.2% respectively. In patients with unilateral RAS, the sensitivities of renogram and IKGFR were 30% and 80% respectively. A significant fall in IKGFR was noted in eight of the 15 ‘normal’ renal units of the unilateral RAS group. In conclusion, individual kidney GFR estimation in combination with captopril renography improved significantly the sensitivity in patients with symmetrical bilateral RAS and unilateral RAS with a small, poorly functioning kidney. A fall in GFR in the normal counterpart of a unilateral RAS kidney may be indicative of ongoing damage in the non-involved kidney.