Tubular function disturbances in chronic glomerulonephritis and their significance for identifying tubulointerstitial lesions.

The tubular and tubulointerstitial renal functions of 237 patients with chronic glomerulonephritis and functional compensation corresponding to their plasma creatinine levels were investigated and the results were compared with the light microscopic findings obtained by examination of kidney interstices obtained by biopsy. Pronounced structural interstitial lesions (TiC) were found in 30% of the cases. Investigation of the predictive values of tubular function data in respect of the presence or exclusion of TiC showed that, although individual parameters of the renal function permit the exclusion of TiC disturbances with a high degree of certainty, the diagnostic value can be enhanced by considering pairs of such parameters. Five parameter combinations were found to have the highest predictive value regarding the diagnosis of TiC. These were disturbed concentration capacity accompanied by reduced ammonia excretion or total acid excretion, reduced water diuresis accompanied by disturbed ammonia excretion or total acid elimination; and, finally, the total acid excretion and maximum dilution capacity. The highest predictive values for the exclusion of TiC are shown by inconspicuous concentration capacity accompanied by normal ammonia excretion, total acid excretion, water diuresis, free water clearance or urine dilution capacity.