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Determinants of plasma PTH and their implication for defining a reference interval
Author(s) -
Rejnmark Lars,
Vestergaard Peter,
Heickendorff Lene,
Mosekilde Leif
Publication year - 2011
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.2010.03894.x
Subject(s) - endocrinology , medicine , vitamin d and neurology , confidence interval , population , parathyroid hormone , body mass index , calcium , chemistry , environmental health
Summary Background To improve the diagnostic sensitivity of PTH measurements, more data on the upper limit of the reference interval for PTH levels were requested at a recent international consensus conference. As PTH levels vary inversely with plasma 25‐hydroxyvitamin D (25OHD) levels and as vitamin D insufficiency is widespread, particular attention should be given to the influence of low vitamin D levels on the PTH reference interval. Aim, design and methods In a cross‐sectional design, including 2316 women aged 17–84, we determined 95% reference interval using a nonparametric approach and studied the effects of potential predictors on plasma PTH levels. Results PTH was a positive function of age, body weight and BMI and inversely associated with total daily calcium intake, smoking, plasma calcium levels and 25OHD levels, all of which explained 16% of the variability in plasma PTH levels. The threshold value for 25OHD levels below which PTH levels started to rise was 82 nmol/l. Plasma PTH levels varied inversely with the seasonal variations in 25OHD levels. Mean PTH level was 4·1 pmol/l with a reference interval equal to 2·0–8·6 pmol/l. Restricting the population in whom the reference interval was calculated to only women with 25OHD levels above 30 or 100 nmol/l lowered the upper limit of the reference interval to 8·4 and 7·1 pmol/l, respectively. Similar, stratification according to age, body mass index, smoking and calcium intake had only minor impact on the reference interval. Conclusion Indices with known effects on plasma PTH levels have only a minor impact on the upper levels of the normative reference interval in women with intact renal function.