The sensitivity of function tests in detecting renal damage in the rat

The possible value of assessing organ function in long-term feeding tests is discussed. The sensitivity of the concentration test, phenol red test, dilution test, urine cell and albumin estimation, C in, C pah, Tm pah, and serum urea determinations, relative kidney weight, and histopathologic examination, in detecting functional impairment or structural damage, were investigated in groups of rats treated to cause acute and longer-term renal damage. Renal tubular damage was caused by administration of uranyl nitrate or sodium phosphate and by choline-deficient diet; and damage primarily to the glomeruli, by injections of nephrotoxic serum. The effects of a reduced food intake were studied in one group of rats. Histologic examination was the most sensitive method of detecting renal damage. Relative kidney weight was increased in most groups of rats with renal injury. Decrease in the rate of body weight gain and the appearance of the organs at autopsy were insensitive criteria in detecting renal damage. Estimation of urine cell and albumin contents was a valuable indication of renal integrity and the concentration test was the most sensitive of the function tests examined. The kidneys of rats fed on a restricted amount of diet appeared to be normal when examined by histologic techniques, but tests indicated that they functioned less efficiently than in control animals. The necessity for using control animals of a suitable nutritional status, when examining and interpreting the results of function and renal weight studies, is emphasized.