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[A study of serum phosphorus and renal phosphate excretion in children of different age groups]
1Department of Pediatrics, Tri-Service General Hospital, Taipei, Taiwan, R.O.C.
Insights
Serum phosphorus concentration is highest in neonates and decreases with age in Chinese children, similar to foreign findings. Increased intestinal absorption and lower kidney filtration may cause high phosphorus levels.
Area of Science:
- Pediatric Endocrinology
- Renal Physiology
- Nutritional Biochemistry
Background:
- High serum phosphorus concentrations have been reported in foreign children.
- Understanding ethnic variations and contributing factors is crucial for pediatric health.
Purpose of the Study:
- To compare serum phosphorus levels in ethnic Chinese children with foreign data.
- To investigate potential causes of elevated serum phosphorus concentrations in children.
Main Methods:
- Studied 1,189 individuals: neonates (2-7 days), children (6-18 years), and adults.
- Measured serum phosphorus concentration and calculated maximal tubular phosphate reabsorption rates.
- Utilized Walton-Bijvoet nomogram and side-rule method for renal phosphate threshold determination.
Main Results:
- Serum phosphorus concentration was highest in neonates and decreased with age, with no significant sex differences.
- Renal phosphate threshold concentration followed a similar age-related decline.
- Neonate phosphorus levels: 7.20-7.65 mg/dl; children (6-11 yrs): 5.14-5.50 mg/dl; adolescents (12-18 yrs): 4.31-4.96 mg/dl.
Conclusions:
- Age-dependent changes in serum phosphorus and renal phosphate threshold observed in Chinese children align with international findings.
- Potential factors for high serum phosphorus include increased intestinal phosphorus absorption, low glomerular filtration rate (GFR), and reduced phosphorus clearance.
- Enhanced intestinal absorption of phosphorus is a significant factor, particularly for growing children.
Abstract:
To further elucidate the data of high serum phosphorus concentration reported for foreign children, this study compared the values of serum phosphorus concentration in ethnic Chinese children with foreigners' results, and investigated the potential causes of high serum phosphorus concentration. This study included 33 healthy term male neonates from 2-3 days to 5-7 days old, 1,094 children of 6-18 years old (elementary school-senior high school) and 62 adults. A total of 1,189 persons were studied. Value of serum phosphorus concentration showed no significant difference between boys and girls, and no age dependency; there was notable change in serum phosphorus concentration in growing children of different ages. The mean values of serum phosphorus concentration of neonates aged 2-3 days and 5-7 days (7.20 mg/dl and 7.65 mg/dl, respectively) were the highest; boys aged 6-11 years 5.15-5.50 mg/dl and girls aged 6-11 years 5.14-5.28 mg/dl were the second; boys aged 12-18 years 4.31-4.94 mg/dl and girls aged 12-18 years 4.44-4.96 mg/dl were the lowest. These findings are similar to the conclusions of foreign reports that the older the subjects of the study, the less their serum phosphorus concentration. The maximal transport rates of tubular phosphate reabsorption were determined from a Walton-Bijvoet nomogram using the side-rule method they recommend. The renal phosphate threshold concentration of neonates aged 2-3 days 8.41 mg/100 ml GFR and 5-7 days 7.76 mg/dl GFR was also the highest; boys aged 6-11 years 5.84-6.32 mg/dl GFR and girls aged 6-11 years 5.82-6.10 mg/dl GFR and 5.44-6.10 mg/dl GFR was the second; adult males 3.51 mg/dl GFR and adult females 3.62 mg/dl GFR was the lowest. Increased intestinal absorption of phosphorus, low GFR and low clearance of phosphorus might be the contributing factors to cause high serum phosphorus concentration. Although high renal phosphate threshold capacity is important, increased absorption of phosphorus by G-I tract seems to be another factor in accordance with the need of phosphorus of the growing body cells.