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Renal magnesium handling in infants and children
G Ariceta1, J Rodríguez-Soriano, A Vallo
1Department of Paediatrics, Hospital de Cruces and Basque University School of Medicine, Bilbao, Pais Vasco, Spain.
Insights
Infants show higher plasma magnesium levels and a higher urine magnesium to creatinine ratio compared to children. This indicates no renal immaturity in magnesium handling during infancy.
Area of Science:
- Pediatric Nephrology
- Mineral Metabolism
- Human Physiology
Background:
- Renal magnesium (Mg) handling in infants and children is not well understood.
- Recent advancements allow measurement of diffusible plasma Mg fractions.
Purpose of the Study:
- To assess Mg homeostasis in healthy infants and children.
- To compare Mg handling between infants and children.
Main Methods:
- Measured total and ultrafilterable plasma Mg in 45 infants (1-12 months) and 63 children (1-15 years).
- Analyzed urine magnesium to creatinine ratio (Umg/Ucr) and fractional Mg excretion.
- Determined renal Mg threshold during Mg infusion in six children.
Main Results:
- Infants had significantly higher total and ultrafilterable plasma Mg than children.
- The Umg/Ucr ratio was significantly higher in infants.
- Fractional Mg excretion was similar between infants and children.
- Renal Mg threshold in children approximated adult values.
Conclusions:
- Infants do not exhibit functional immaturity in renal tubular Mg reabsorption.
- Higher Umg/Ucr in infants is likely due to lower urinary creatinine excretion per lean body mass, not increased Mg excretion.
Abstract:
Renal handling of magnesium (Mg) has been incompletely studied during infancy and childhood due to the difficulty, until recently, of measuring the diffusible fraction of plasma Mg. In the present investigation this methodology has been used to assess Mg homeostasis in 45 healthy infants, aged 1 to 12 months, and in 63 healthy children, aged 1 to 15 years. When compared to children, infants had significantly higher plasma values (mean +/- SD) for both total (0.76 +/- 0.08 versus 0.70 +/- 0.06 mmol l-1; p < 0.001) and ultrafilterable Mg (0.51 +/- 0.07 versus 0.49 +/- 0.04 mmol l-1; p < 0.05). No significant correlations were present between values of plasma Mg and plasma concentrations of calcium, creatinine, total protein or albumin. The ratio Umg/Ucr, calculated in the second morning urine (median, 3rd-97th centiles), was also significantly higher during infancy (0.023, 0.009-0.07 versus 0.015, 0.006-0.04; p < 0.001). On the contrary, fractional excretion of Mg (median, 3rd-97th centiles) was identical in both age groups and did not correlate significantly with age (infants: 3.2, 1.0-7.8%, children 3.4, 1.6-8.1%; p = NS). During a Mg infusion, carried out in six children, we could establish an approximative value for renal Mg threshold (plasma ultrafilterable Mg = 0.50 mmol l-1) close to that found in adults. These results indicate that no functional immaturity is present during infancy for renal tubular reabsorption of Mg and that the high Umg/Ucr ratio observed in this age group is a phenomenon not dependent on a higher urinary Mg excretion but probably related to a lower urinary creatinine excretion per unit of lean body mass.