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Serum intact parathyroid hormone and ionised calcium concentration in children with renal insufficiency
S E Ledermann1, A Johnson, M J Dillon
1Renal Unit, Hospital for Sick Children, London, UK.
Insights
Intact parathyroid hormone (i-PTH) assays are reliable in children with chronic renal insufficiency (CRI), independent of kidney function. Ionized calcium (PCa2+) levels correlate with total calcium but can be misleading due to anion complexing in CRI.
Area of Science:
- Pediatric Nephrology
- Endocrinology
- Clinical Chemistry
Background:
- Chronic renal insufficiency (CRI) in children presents complex metabolic challenges.
- Accurate assessment of mineral and bone disorders is crucial for managing pediatric CRI.
- Traditional parathyroid hormone (PTH) assays can be affected by renal function.
Purpose of the Study:
- To evaluate the utility of intact parathyroid hormone (i-PTH) assay in children with CRI.
- To assess the relationship between i-PTH, ionized calcium (PCa2+), and other biochemical markers.
- To investigate calcium complexing in pediatric CRI.
Main Methods:
- Utilized an immunoradiometric assay for i-PTH measurement.
- Measured plasma ionized calcium (PCa2+) and total calcium (tPCa).
- Analyzed correlations between i-PTH, PCa2+, plasma creatinine (PCr), albumin, tubular reabsorption of phosphate, and alkaline phosphatase.
Main Results:
- i-PTH showed poor correlation with PCr, indicating independence from renal function in treated children.
- i-PTH responded clearly to changes in low tPCa and PCa2+.
- A significant positive correlation was observed between tPCa, PCa2+, and the fraction of ionized calcium.
- Low PCa2+ with a low ionized fraction was frequent, suggesting calcium complexing by anions in CRI.
Conclusions:
- The i-PTH assay is a reliable tool for assessing parathyroid status in pediatric CRI, unaffected by renal function.
- Ionized calcium measurement is important, but anion complexing can complicate interpretation of total calcium levels in CRI.
- Further investigation into calcium-anion interactions in pediatric CRI is warranted.
Abstract:
We report our experience of the use of an immunoradiometric assay for intact parathyroid hormone (i-PTH) and the measurement of plasma ionised calcium concentration (PCa2+) in 73 children with chronic renal insufficiency (CRI); plasma creatinine concentration (PCr) 52-856 mumol/l. There was a poor correlation between i-PTH and PCr (r = 0.10, n = 552) compared with that for C-terminal PTH and PCr (r = 0.60, n = 248), suggesting that the i-PTH assay is independent of renal function in this group of treated children. A clear response of i-PTH to a low total plasma Ca (tPCa) and PCa2+ was observed. There was a significant positive correlation between both tPCa and PCa2+ (r = 0.50, n = 389) and the fraction of Ca2+ (the fraction of tCa which was ionised) and PCa2+ (r = 0.50, n = 389). The finding of a low or normal PCa2+ with a low calculated fraction of Ca2+ was frequently observed, i.e. the measured tPCa was unexpectedly high, suggesting complexing of Ca2+ by accumulated anions in CRI. There was a poor relationship between the plasma albumin concentration and both bound plus complexed Ca (tPCa minus PCa2+) and the fraction of Ca2+ (r = 0.15 and -0.17, respectively). The positive predictive value for a raised i-PTH of a tubular reabsorption of phosphate of less than 80% was 0.87, and of an alkaline phosphatase greater than 800 U/l was 0.37.(ABSTRACT TRUNCATED AT 250 WORDS)