The biphasic nature of renal functional recovery following relief of chronic obstructive uropathy.

Twenty-one patients with chronic obstructive uropathy due to high pressure chronic retention of urine underwent renal functional assessment both during the period of obstruction and repeatedly up to 3 months following its relief. Glomerular filtration rate (GFR) was determined using clearance of 99mTc-DTPA and iohexol. Creatinine, water, urea and electrolyte excretion was assessed from timed urine collections. Excretion of water, urea and electrolyte was normal during obstruction but increased dramatically immediately following relief (e.g. sodium 110 to 234 mmol/24 h). Values returned to normal by 2 weeks (sodium excretion 148 mmol/24 h). No further significant changes occurred up to 3 months. Mean 99mTc-DTPA and iohexol clearances during obstruction were 59.0 and 50.5 ml/min respectively. Following relief of obstruction, no significant improvement occurred at 2 weeks but did at 3 months (mean = 68.4 and 55.7 ml/min). Mean creatinine clearance during obstruction was 32.5 ml/min. This improved 2 days following relief to 46 ml/min. No further improvement was seen until 3 months (mean = 57.3 ml/min). It was concluded that recovery of renal function from obstructive injury occurs in two phases, an early tubular phase lasting up to 2 weeks and a later, predominantly glomerular phase, between 2 weeks and 3 months. There is some disparity between creatinine clearance and more accurate measurements of GFR which may be explained by tubular excretion of creatinine in the early phase of recovery.