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Renal handling of calcium in the early newborn period
Insights
Newborn kidney function in preterm and fullterm infants shows that urinary calcium excretion increases with gestational age and is not impaired, suggesting it doesn't cause neonatal hypocalcemia.
Area of Science:
- Neonatal Physiology
- Renal Function in Infants
- Calcium Metabolism
Background:
- Neonatal hypocalcemia is a common concern in preterm infants.
- Understanding renal handling of calcium in newborns is crucial for managing calcium balance.
- Previous studies have not fully elucidated calcium excretion patterns in relation to gestational age and renal function.
Purpose of the Study:
- To investigate urinary calcium excretion in well preterm and fullterm infants within the first 48 hours of life.
- To determine the relationship between urinary calcium excretion and gestational age, serum calcium, glomerular filtration rate, and cyclic AMP.
- To assess the kidney's ability to conserve calcium compared to sodium in early neonatal life.
Main Methods:
- Studied two matched groups of 28 clinically well preterm and fullterm infants.
- Analyzed urinary calcium excretion in relation to gestational age (28-40 weeks).
- Correlated urinary calcium with serum calcium, glomerular filtration rate, and urinary cyclic AMP.
Main Results:
- Urinary calcium excretion positively correlated with gestational age, serum calcium, glomerular filtration rate, and urinary cyclic AMP.
- Calcium excretion was independent of sodium and calcium intake, and urinary sodium and phosphate excretion.
- Fractional calcium excretion was <1.0% in infants ≤32 weeks gestation, unlike sodium excretion (>2.5%).
Conclusions:
- The newborn kidney in preterm infants (≤32 weeks gestation) does not show impaired calcium conservation.
- Neither calcium intake nor excretion appears to significantly affect urinary calcium in well newborns.
- Excess calcium excretion or serum phosphate levels are unlikely contributors to early neonatal hypocalcemia.
Abstract:
Urinary calcium excretion was studied in two matched groups of 28 clinically-well preterm and fullterm infants between 24 and 48 hours of life. In the developmental period from 28 to 40 weeks gestation, urinary calcium excretion was positively correlated to the gestational age (r = 0.583, P less than 0.01), serum calcium levels (r = 0.512, P less than 0.01), the rate of glomerular filtration (r = 0.715, P less than 0.001), and urinary cyclic AMP excretion (r = 0.717, P less than 0.001). Urinary calcium excretion was independent of sodium and calcium intake, and urinary sodium and phosphate excretion. The mean fractional total calcium excretion and fractional ionized calcium excretion in babies less than or equal to 32 weeks was less than 1.0%, compared to greater than 2.5% for sodium. Serum calcium levels were positively correlated with gestational age (r = 0.803, P less than 0.001), and serum phosphate levels (r = 0.85, P less than 0.001). Whole blood ionized calcium levels were positively correlated to gestational age (r = 0.625, P less than 0.001), and serum total calcium levels (r = 0.440, P less than 0.05). The newborn kidney in babies less than or equal to 32 weeks gestation, did not have impaired conservation of calcium as for sodium; and neither sodium nor calcium intake appeared to affect urinary calcium excretion in the well newborn infant. Probably neither excess excretion of calcium nor serum phosphate levels contribute to early neonatal hypocalcemia.