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Serum ionized calcium concentrations in normal neonates
J L Loughead1, F Mimouni, R C Tsang
1Department of Pediatrics, University of Cincinnati College of Medicine, OH 45267-0541.
Insights
Newer electrode technology reveals higher normal serum ionized calcium (iCa) levels in newborns. Current reference ranges, established with older methods, may not accurately reflect typical iCa concentrations in neonates during the first 24 hours of life.
Area of Science:
- Clinical Chemistry
- Neonatal Medicine
- Biomedical Engineering
Background:
- Adult serum ionized calcium (iCa) concentrations are higher with modern ion-selective electrodes (ISEs) than with older ones.
- Existing neonatal normative ranges for iCa were established using outdated electrodes and lack standardization for age and conditions.
Purpose of the Study:
- To determine accurate neonatal normative ranges for serum iCa concentrations using contemporary ISE technology.
- To compare new iCa ranges with previously published reference values for neonates.
Main Methods:
- Serum iCa concentrations were measured in 30 term infants at birth, 2 hours, and 24 hours of age.
- Infants were carefully screened to minimize confounding factors affecting iCa levels.
- Measurements utilized newer, highly sensitive, ion-selective electrodes.
Main Results:
- Mean serum iCa concentrations showed a decline from birth (1.45 mmol/L) to 2 hours (1.33 mmol/L) and 24 hours (1.23 mmol/L).
- The 95% confidence interval for iCa at 24 hours ranged from 1.10 to 1.36 mmol/L.
- Normal neonatal iCa ranges derived from newer ISEs are higher than previously published reference values.
Conclusions:
- Current reference ranges for neonatal serum iCa may be inaccurate due to the use of older electrode technology.
- Higher normal iCa concentrations are observed in neonates when measured with modern, sensitive ISEs.
- Revised normative data are needed for accurate clinical assessment of neonatal iCa.
Abstract:
Adult serum ionized calcium (iCa) concentrations are higher when using the newer, highly sensitive, ion-selective electrodes compared with older electrodes. Currently used neonatal normative ranges were established using older electrodes and not under standardized conditions or age. Thirty term infants, carefully screened to exclude confounding factors that could affect serum iCa concentration, were studied at birth and 2 and 24 hours of age for serum iCa concentrations. Mean concentrations declined from 1.45 mmol/L (5.82 mg/dL) at birth to 1.33 mmol/L (5.34 mg/dL) at 2 hours to 1.23 mmol/L (4.92 mg/dL) at 24 hours. The 95% confidence limits at 24 hours ranged from 1.10 to 1.36 mmol/L (4.40 to 5.44 mg/dL). Using newer ion-selective electrodes, normal neonatal ranges for iCa concentrations during the first 24 hours of age are higher than published references.