The renal functional reserve in health and renal disease in school age children.

The capacity to increase the glomerular filtration rate (GFR) in response to stimuli is a characteristic of the healthy kidney. To establish normal limits of this functional reserve is of clinical relevance because its loss may be the earliest indication of renal damage. For this purpose we have used a method applicable in clinical practice: one-hour clearances of creatinine (CCr) done under water diuresis, before (unstimulated) and two hours after (stimulated) a test meat meal, taking a single postmeal blood sample. Urine collection was done by voluntary voiding under direct supervision. In studies done in 14 control subjects, inulin clearance (CIn)/CCr ratios were (mean +/- SEM) 1.04 +/- 0.05 and 0.96 +/- 0.03, in unstimulated and stimulated clearances, respectively. In studies repeated at three to nine week intervals, we found a variation coefficient (mean +/- SEM) of 24.5 +/- 3.11% and 9.25 +/- 1.43% (P less than 0.001) for the unstimulated and stimulated CCr, respectively. The corresponding values for CIn were 19.3 +/- 2.36% and 9.17 +/- 1.19% (P less than 0.001), suggesting that stimulated GFR values are more stable. Unstimulated and stimulated GFR and renal functional reserve (stimulated CCr - unstimulated CCr) were studied in 260 school aged children, ages 6 to 16 years (140 boys and 120 girls). The distribution of the renal functional reserve was approximately Gaussian but the distribution of the urinary creatinine excretion, unstimulated and stimulated GFR had considerable positive skewness.(ABSTRACT TRUNCATED AT 250 WORDS)