Parathormone, bone alkaline phosphatase and 25-hydroxyvitamin D status in a large cohort of 1200 children and teenagers.

Objectives: 25-Hydroxyvitamin D (25(OH)D), parathyroid hormone (PTH) and bone alkaline phosphatase (BALP) are biomarkers of calcium/phosphate metabolism and bone turnover. Although vitamin D deficiency is a well-known cause of secondary hyperparathyroidism, few studies have considered vitamin D status when establishing reference ranges. In this study, we report PTH levels according to the vitamin D status and BALP levels in a large cohort of 1200 children. Additionally, we provide PTH pediatric reference values according to 25(OH)D status as well as BALP pediatric reference ranges.Methods: Serum samples from 1200 children (equally distributed from 5 months to 20 years old) who underwent blood sampling for allergy exploration were used to quantify 25(OH)D, PTH and BALP.Results: The percentage of vitamin D deficient children (<20 ng/ml) progressively increased during childhood starting from 7% in the 0 to 2 year-old subgroup to a mean of at least 50% among teenagers. PTH levels inversely mirrored 25(OH)D concentrations for all age and gender subgroups, and 25(OH)D deficient subgroups presented higher PTH levels than their non-deficient counterparts. In the non-deficient 25(OH)D population, PTH levels were the highest at 11 years old for girls and 14 years old for boys. BALP results were slightly increased during childhood and showed a constant decrease during teenage years starting from 12 years old for girls and 14 years old for boys.Conclusion: Our results highlight the inverse relationship between PTH and 25(OH)D in children and the need for a well characterized 25(OH)D population to establish pediatric reference ranges for PTH.

Simultaneous measurement of 25(OH)-vitamin D and 24,25(OH)2-vitamin D to define cut-offs for CYP24A1 mutation and vitamin D deficiency in a population of 1200 young subjects.

Background Simultaneous measurement of 25(OH)D and 24,25(OH)2D is a new tool for predicting vitamin D deficiency and allows evaluating CYP24A1 lack of function. Interpretation of 24,25(OH)2D should be performed according to 25(OH)D levels and a ratio, called the vitamin D metabolite ratio (VMR) has been proposed for such a purpose. Unfortunately, the VMR can be expressed in different ways and cannot be used if 24,25(OH)2D concentrations are undetectable. Here, we propose evaluating the enzyme activity taking into consideration the probability that a normal population presents undetectable 24,25(OH)2D concentrations according to 25(OH)D levels. We thus retrospectively measured 25(OH)D and 24,25(OH)2D in a population of 1200 young subjects to evaluate the 25(OH)D threshold above which the enzyme was induced. Methods Serum samples from 1200 infants, children, adolescent and young adults were used to simultaneously quantify 25(OH)D and 24,25(OH)2D by LCMS/MS. Results Median (interquartile range [IQR]) levels were 20.6 (14.4-27.2) ng/mL for 25(OH)D. 172 subjects (14.3%) presented 24,25(OH)2D values below the LOQ. When 25(OH)D values were <11 ng/mL, 63.1% of subjects presented undetectable 24,25(OH)2D concentrations. Percentage decreased with increasing 25(OH)D values to become 19.7% for 25(OH)D comprised between 12 and 15 ng/mL, 5.1% for 25(OH)D between 16 and 20 and 0.7% for 25(OH)D >21 ng/mL. Conclusions We suggest using a statistical approach to evaluate CYP24A1 function according to 25(OH)D concentrations. Our results also show that vitamin D deficiency, as defined biochemically, could be around 20 ng/mL in infants, children, adolescent and young adults and that vitamin D deficiency could be evaluated on a more individual basis.

IDS iSYS automated intact procollagen-1-N-terminus pro-peptide assay: method evaluation and reference intervals in adults and children.

BACKGROUND: We carried out a technical evaluation of the Immunodiagnostic Systems (IDS) automated intact procollagen-I N-terminus propeptide (PINP) assay on the iSYS platform, and established reference intervals for PINP in both adults and children. METHODS: Assay imprecision, recovery and interference were studied. Serum and plasma values were compared, and PINP stability was assessed. Using 828 specimens, IDS iSYS intact PINP and Roche E170 total PINP values were compared. Specimens from 597 adults and 485 children and adolescents were used to establish reference intervals for intact PINP. RESULTS: The method demonstrated good recovery and acceptable imprecision. The assay was unaffected by icterus and lipaemia, but haemolysis decreased measured PINP. Serum and plasma values were comparable. There was a non-linear relation between IDS intact and Roche total PINP values. Pre- and post-menopausal women had comparable PINP values, but there was a difference between women of different age groups. Serum PINP in men showed a decline in young age up to 45 years, but remained steady thereafter. Separate reference intervals were established for four age groups in women and for two age groups in men. Data for children were partitioned into four-year age groups, and these showed PINP to be high with no major gender differences until 12 years of age. Thereafter, values in females decreased in 13-16 years age groups and further in 17-20 years age groups, whereas PINP increased in boys of 13-16 years of age with a subsequent decline at 17-20 years. CONCLUSIONS: The IDS iSYS PINP intact assay appears to be reliable. We have established gender- and age-related reference intervals for children and adults based on a relatively large healthy North European population.

Technical and clinical evaluation of the VITROS® Immunodiagnostic Products 25-OH Vitamin D Total Assay--comparison with marketed automated immunoassays and a liquid chromatography-tandem mass spectrometry method.

BACKGROUND: The study was conducted to evaluate the technical and clinical performance of the VITROS® Immunodiagnostic Products 25-OH Vitamin D Total Assay, and compare it with the performance of five marketed automated assays and a liquid chromatography/mass spectrometry reference method (LC-MS/MS). METHODS: Three hundred patient serum samples were used to compare the correlation of the VITROS® 25-OH Vitamin D Total Assay with both the other immunoassays and the LC-MS/MS method, using Passing-Bablok regression and Bland-Altman analyses. Concordance of the diagnosis of vitamin D status was calculated to test the agreement between the different assays. In addition, samples containing vitamin D2 were used to test the assay's ability to detect the D2 form of the vitamin. RESULTS AND CONCLUSIONS: These results from the VITROS® 25-OH Vitamin D Total Assay generally correlated well with those from most of the marketed immunoassays. Cross-reactivity of the D2 form was calculated as being close to 100%. Additionally, we found substantial variability in performance amongst the various assays, which suggests the need for optimisation and recalibration of commercial methods.

Analytical evaluation of the new Abbott Architect 25-OH vitamin D assay.

OBJECTIVES: Validation of the Architect 25-OH vitamin D assay. DESIGN AND METHODS: Determination of repeatability, reproducibility, accuracy profile and 25(OH)-vitamin D2 recovery on native samples. Comparison with DiaSorin Liaison and RIA. RESULTS AND CONCLUSION: Coefficients of variation: <6% (13.6 ng/mL) and 2.2% (78.1 ng/mL). Functional sensitivity: 5 ng/mL. Accuracy profile shows that the method is validated between 13.6 and 78.1 ng/mL. Recovery of 25(OH)D2: 75,8%( 95% CI: 61.9-89.7%). Good correlation with DiaSorin RIA and Liaison <50 ng/mL; above this threshold a systematic positive bias was observed.

Analytical validation of the Liaison Calcitonin_II-Gen (DiaSorin).

BACKGROUND: We validated the DiaSorin Liaison Calcitonin_II-Gen, an improved method for calcitonin (CT) measurements, compared this method with the Cisbio_h-CT kit and established the reference range of CT in a normal adult population. METHODS: We determined the precision, functional sensitivity, traceability to the 2nd IS 89/620, linearity and measurement uncertainty, accuracy profile and ß-expectation limits. We evaluated the specificity, the susceptibility to human anti-animal antibodies (HAMA), hook-effect and carry over. To establish a reference range, we selected 267 adults without renal insufficiency presenting with normal thyroid stimulating hormone (TSH), free thyroxin (T4) and calcium concentrations and without anti-thyroglobulin antibodies as our "reference" healthy population. We compared the method with Cisbio on 250 consecutive and 45 samples from a post-pentagastrin stimulation test. RESULTS: Precision (expressed as CV) was < 10% for the measurement range, functional sensitivity: 5.3 ng/L and the method was found linear until to a 1/10 dilution. Uncertainty ranged from 25% to 7.2%, and the risk that one result falls out of the ± 20% acceptance limits was < 5% between 2.9 and 1513 ng/L. The Bland and Altman plot showed no systematic bias between the two methods. The test is still prone to HAMA influence, does not present any hook-effect, although carry over was observed. Ninety-five percent of our adult reference population showed CT concentrations < 7.4 ng/L, with an important gender difference: 95% of the men showed CT values < 9.8 ng/L, whereas 95% of women were < 4.0 ng/L. CONCLUSIONS: The Liaison Calcitonin_II-Gen is an analytically robust method. The important difference in gender observed in our population might lead to re-evaluation of the generally used "10 ng/L" cut-off in a multicentre prospective study.

Analytical validation of serum bone alkaline phosphatase (BAP OSTASE) on Liaison.

BACKGROUND: The goal of this study was to validate the DiaSorin Liaison BAP OSTASE, a new method for measurement of bone alkaline phosphatase (BAP), and to compare this method with the Beckman-Coulter Access Ostase. We also wanted to establish the reference range for BAP in adults and children. METHODS: We determined the precision, functional sensitivity, recovery, linearity and measurement uncertainty, accuracy profile and beta-expectation limits. We defined an adult reference interval using individuals with 25-OH vitamin D >80 nmol/L, parathormone <58 ng/L, and normal calcium, phosphorous and estimated glomerular filtration rate. Each adult subclass (men/non-menopausal women/menopause women) contained 120 individuals. We also determined the 2.5th and 97.5th percentiles from a population of 450 children, stratified according to age and gender. RESULTS: The results of the validation showed: precision <6%, functional sensitivity <0.74 microg/L, mean recovery 98.8+/-4.2% and good linearity. Relative uncertainty ranged from 9.0% to 12.9%, and the risk of one result falling out of the +/-15% acceptance limits was <5% for concentrations between 7 and 94 microg/L. The Bland-Altman plot showed no systematic bias between the two methods. In adults, we did not find any statistical difference between the different subclasses. The upper limit of normality observed in the entire population (n=360) was 21.3 microg/L (90% CI: 18.3-24.2 microg/L). CONCLUSIONS: The Liaison BAP OSTASE is a robust method, and is completely validated between 7 and 93 microg/L: in this range, 95% of the values obtained will be within +/-15% of the true value.