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

• Published in: Kidney international Vol. 34; no. 6; pp. 809 - 816
• Main Authors: Molina, Enrique, Herrera, José, Rodríguez-Iturbe, Bernardo
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 01.12.1988; Nature Publishing
• Subjects: Biological and medical sciences; Child; Creatinine - metabolism; Diuresis; Female; Glomerular Filtration Rate; Glomerulonephritis; Humans; Kidney - physiology; Kidney Diseases - physiopathology; Male; Medical sciences; Nephrology. Urinary tract diseases; Nephropathies. Renovascular diseases. Renal failure; Reference Values; Human; School age; Urinary system disease; Glomerular filtration; Nephropathy; Child
• ISSN: 0085-2538; 1523-1755
• DOI: 10.1038/ki.1988.254

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 < 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 < 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. Normal limits (ml · min-1 · 1.73m-2) for stimulated CCr are 76.4 to 220.5 (10 and 90 percentiles), with a median of 134.5. There were no age-related differences. Unstimulated CCr was higher in males (P < 0.001); but stimulated CCr was similar in both sexes. The renal functional reserve had a negative correlation (R = - 0.542, P < 0.0001) with unstimulated CCr and a positive correlation (R = 0.611, P < 0.0001) with the stimulated CCr. A nomograph was constructed with the 10 and 90 percentiles of the unstimulated and stimulated CCr and renal functional reserve. Studies done in 21 patients with CCr ranging from 25ml · min-1 · 1.73m-2 to 142ml · min-1 · 1.73m-2 demonstrated that absent or diminished renal functional reserve is present in patients with renal disease and normal baseline CCr. Dietary protein restriction was associated with a fall in baseline glomerular filtration, but the stimulated levels remained unchanged and, consequently, the renal functional reserve increased. Determination of stimulated GFR and renal functional reserve may be useful in following the effects of therapeutic intervention in the pre-azotemic stage of renal disease.