Serum iPTH range in a reference population: From an integrated approach to vitamin D prevalence impact evaluation

Characterisation of parathyroid hormone concentration in extremely preterm or very low birthweight infants in routine clinical screening for metabolic bone disease: A service evaluation cohort study

AIM

To characterise parathyroid hormone (PTH) concentrations in infants at high risk for metabolic bone disease, in order to assist clinical decisions around the use of PTH for screening.

METHODS

Infants born under 28 weeks' postmenstrual age or with birthweight under 1.5 kg in a tertiary neonatal unit in the UK were included. Clinical guidance was to assess PTH concentration in the first 3 weeks after birth. Clinical information was extracted from prospective records.

RESULTS

Sixty-four infants had mean birth gestation of 26 weeks and birthweight of 882 g. Median PTH (sent on median day 18 of life) was 9.2 pmol/L (interquartile range 5.3-17 pmol/L). Sixty-seven per cent of infants had a PTH greater than 7 pmol/L. For 22% of the infants, raised PTH was not accompanied by abnormal phosphate or alkaline phosphatase. Eighty-nine per cent of infants tested were insufficient or deficient for 25-hydroxyvitamin D.

CONCLUSIONS

Universal screening highlights the high frequency of high PTH in this high-risk population, implying a need for calcium supplementation. A considerable number of infants would not be identified as showing potential signs of metabolic bone disease if the assessment excludes the use of PTH. The high level of 25-hydroxyvitamin D deficiency may be a confounder.

Threshold of 25(OH)D and consequently adjusted parathyroid hormone reference intervals: data mining for relationship between vitamin D and parathyroid hormone

PURPOSE

By recruiting reference population, we aimed to (1): estimate the 25(OH)D threshold that maximally inhibits the PTH, which can be defined as the cutoff value for vitamin D sufficiency; (2) establish the PTH reference interval (RI) in population with sufficient vitamin D.

METHODS

Study data were retrieved from LIS (Laboratory Information Management System) under literature suggested criteria, and outliers were excluded using Tukey fence method. Locally weighted regression (LOESS) and segmented regression (SR) were conducted to estimate the threshold of 25(OH)D. Multivariate linear regression was performed to evaluate the associations between PTH concentration and variables including 25(OH)D, gender, age, estimated glomerular filtration rate (EGFR), body mass index (BMI), albumin-adjusted serum calcium (aCa), serum phosphate(P), serum magnesium(Mg), and blood collection season. Z test was adopted to evaluate whether the reference interval should be stratified by determinants such as age and gender.

RESULTS

A total of 64,979 apparently healthy subjects were recruited in this study, with median (Q1, Q3) 25(OH)D of 45.33 (36.15, 57.50) nmol/L and median (Q1, Q3) PTH of 42.19 (34.24, 52.20) ng/L. The segmented regression determined the 25(OH)D threshold of 55 nmol/L above which PTH would somewhat plateau and of 22 nmol/L below which PTH would rise steeply. Multivariate linear regression suggested that gender, EGFR, and BMI were independently associated with PTH concentrations. The PTH RI was calculated as 22.17-72.72 ng/L for subjects with 25(OH)D ≥ 55 nmol/L with no necessity of stratification according to gender, age, menopausal status nor season.

CONCLUSION

This study reported 25(OH)D thresholds of vitamin D sufficiency at 55 nmol/L and vitamin D deficiency at 22 nmol/L, and consequently established PTH RIs in subjects with sufficient vitamin D for northern China population for the first time.

UK Reference Intervals for Parathyroid Hormone Using Abbott Methods

Background: Diagnosis of hyperparathyroidism requires measurement of parathyroid hormone (PTH) in the context of the plasma calcium and other factors, such as vitamin D status and renal function. Accurate classification depends upon an appropriate population reference interval. We examined local population plasma PTH reference intervals at four different UK sites using a common platform. Methods: Plasma PTH results were extracted from laboratory information systems at four different UK sites, all using the Abbott Architect i2000 method. We included only people with normal adjusted serum calcium, magnesium, vitamin D, and renal function. Following outlier rejection lower and upper reference limits were derived. Results: An overall reference interval for plasma PTH of 3.0-13.7 pmol/L was observed using a non-parametric approach compared to 2.9-14.1 pmol/L using a parametric approach, notably higher than the manufacturer's representative range of 1.6-7.2 pmol/L. We also noted statistically significant differences (p < 0.00001) between some sites with upper limits ranging from 11.5 to 15.8 pmol/L which may be due to different population characteristics of each group. Conclusion: Locally derived reference intervals may be beneficial for UK populations and revised upper thresholds are necessary when using the Abbott PTH method to avoid inappropriate classification of patients as having hyperparathyroidism.

Threshold for Relationship between Vitamin D and Parathyroid Hormone in Chinese Women of Childbearing Age

Background: The aim of this study was to assess the relationship between serum 25-hydroxyvitamin D [25(OH)D] and serum intact parathyroid hormone (PTH) in Chinese childbearing women, and to estimate the optimum threshold of 25(OH)D that maximally inhibits the PTH, which is considered to be the optimal status for vitamin D sufficiency. Methods: Serum samples were selected from the biological samples' bank of the Chinese Chronic Diseases and Nutrition Survey (CCDNS) 2015. The serum 25(OH)D concentration was determined by liquid chromatography tandem mass spectrometry and the serum PTH was determined by electronic chemiluminescence. Simple linear and partial correlation analysis, locally weighted regression smooth scatterplot (LOESS), nonlinear least squares estimation (NLS), and segmented regression (SR) were utilized to estimate the relationship of 25(OH)D and PTH, and to determine the threshold of 25(OH)D. Results: A total of 1568 serum samples of 25(OH)D concentration and PTH concentration were analyzed. A significant inverse relationship between 25(OH)D and PTH concentration was observed below 15.25 (14.22-16.28) ng/mL, and PTH decreased slowly with the increase of 25(OH)D above 16.75 (15.43-18.06) ng/mL after adjusting by age, latitude, city type, season, corrected calcium, and phosphorus. A very short plateau of PTH was found at 15.25 ng/mL and 16.75 ng/mL in terms of 25(OH)D according to LOESS, NLS, and SR. Conclusions: The serum 25(OH)D was negatively correlated with the serum PTH. The threshold of VitD sufficiency was found in the range of 14.22-18.06 ng/mL in terms of serum 25(OH)D concentration for Chinese childbearing women aged 18-44 years old.