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Technical Briefs |
1
Institute General Pathology and Oncology, Second School of Medicine of Naples, 80138 Naples, Italy
a address
correspondence to this author at: Istituto di Patologia Generale e Oncologia, Seconda Università degli Studi di Napoli, Via S. Andrea delle Dame 2, 80138 Napoli, Italy
Parathyroid hormone (PTH) plays an important role in calcium homeostasis by maintaining the concentration of ionized calcium within the precise limits necessary to achieve metabolic and neuroregulatory functions of this essential mineral (1)(2)(3). PTH produces calcium mobilization from the large skeletal stores into the extracellular fluid, increases absorption of dietary calcium, and decreases renal clearance of urinary calcium (3)(4). Serum PTH assays are an important aid in the assessment of calcium metabolism disorders. The aim of this study was to determine serum intact PTH in a large group of healthy children according to their ages.
We selected 794 healthy children (409 girls, 385 boys), ages 2–16 years, arriving for routine clinical check-ups in the Department of Pediatrics over 4 years (1994–1998). Sample sera were taken at 0800 from non-fasting children.
None of the subjects was receiving any medication, and all were ambulatory. All children with evidence of endocrine, hepatic, renal, or other known diseases were excluded from consideration. All subjects were free from diseases affecting the growth rate and bone metabolism. Phosphate and calcium values were within the reference ranges. A single venous blood sample was obtained, and serum was obtained by centrifugation and stored at -20 °C until assay.
This study was carried out in accordance with the ethics standards of the institution’s human investigation committee, and with the Helsinki Declaration of 1975 (as revised in 1983).
Serum intact PTH was assayed by a two-site immunoradiometric method (Nichols Institute). The assay precision was measured by assaying four samples at different concentrations (40, 60, 133, and 266 ng/L) 30 times in the same assay (mean CVs, 1.8%, 1.6%, 2.5%, and 3.4%, respectively) and 15 times over a 5-week period (mean CVs, 3.8%, 5.6%, 6.1%, and 7.2%, respectively). The minimum detectable concentration (1.0 ng/L) was obtained by 20 replicate measurements of the zero calibrator and calculating the 3 SD threshold for these measurements.
P values were determined using the Student t-test; no significant differences were found between the PTH results for boys and girls in any of the age groups.
The median values and percentiles for each group are shown in Table 1
. In all age groups, the median intact PTH concentrations were
17 ng/L. The mean intact serum PTH in boys and girls was 12.68
± 7.1 ng/L (range, 1.4–35.8 ng/L) and 13.9 ± 8.6 ng/L (range,
1.0–39.0 ng/L), respectively. The confidence intervals for all mean
values are shown in Fig. 1
.
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Serum intact PTH concentrations in healthy children were lower and in a narrower range than our adult (age range, 18–55 years) reference interval for the same assay (1.5–62.8 ng/L) (5)(6)(7).
In the girls, serum PTH concentrations increased after the 8th year and peaked at the 10th to the 14th year, decreasing slightly thereafter (P = 0.20). In contrast, serum PTH values in the boys increased persistently from the 8th until the 16th year.
No significant differences in serum PTH concentrations were seen between boys and girls; however, the girls’ serum PTH concentrations were slightly higher than boys from the 10th to the 12th year and from the 12th to the 14th year. These data could be related to changes in the need for calcium in girls for bone metabolism during puberty (8)(9).
Moreover, our data suggest that serum intact PTH concentrations in children covered narrower ranges than adult values.
With advancing age, PTH blood concentrations progressively increase, whereas calcium concentrations tend to decrease. The most likely explanation of this condition is a reduced intestinal absorption of calcium with an attendant decrease of calcium in blood and a reactive increase of PTH incretion. Calcitonin and vitamin D3 also decrease with age. Most likely, the vitamin D3 decrease is multifactorial, depending on reduced hydroxylation of vitamin D by kidney and liver, inadequate dietary intake, impaired intestinal absorption, and possibly reduced sun exposure.
Although we found no differences in serum intact PTH concentrations with age, our results nevertheless represent a useful set of reference values in children.
Acknowledgments
We thank Marisa Punzo, Angela Sglavo, and Bianca Tesone for excellent technical assistance in the assay procedure.
Footnotes
References
The following articles in journals at HighWire Press have cited this article:
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  C. J. Lamberg-Allardt and H. T Viljakainen 25-Hydroxyvitamin D and functional outcomes in adolescents Am. J. Clinical Nutrition, August 1, 2008; 88(2): 534S - 536S. [Abstract] [Full Text] [PDF]
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