Sequential renography in acute urinary tract obstruction due to stone disease.

A group of 76 patients with urographically proven acute calculus obstruction was studied prospectively using 99mTc-DTPA renography to see if kidneys at risk of irreversible renal damage could be identified. There was a statistically significant relationship between the presence of obstruction on renography and the subsequent requirement for intervention, but not with the degree of obstruction (partial or severe). Stones over 5 mm in size are highly likely to cause obstruction, a drop in relative renal function and require intervention. In all, 14 patients sustained a drop in relative renal function of greater than 7% on renography and 12 of these returned to normal limits when their calculi had been passed or removed. The 2 kidneys whose function remained impaired had fallen below 25% of overall renal function and both patients had received prior treatment for their calculi. No patient who presented de novo suffered any permanent loss of ipsilateral renal function. The results confirm that the criteria for intervention were well founded and emphasise the importance of achieving a stone-free state after primary treatment. Renography is recommended for stones over 5 mm in size, those in the middle and upper ureter and for those patients discharged with a stone in situ.