Original ArticleReference Range for Serum Parathyroid Hormone
Section snippets
INTRODUCTION AND BACKGROUND
The earliest radioimmunoassay for parathyroid hormone (PTH) used polyclonal antisera directed against intact PTH(1-84) (1). Most early assays were directed against the middle or C-terminus of the PTH peptide (2). Investigators soon found that several fragments of PTH in serum were derived from the parathyroid glands and from peripheral metabolism of PTH(1-84) (3., 4., 5., 6., 7., 8., 9., 10., 11.). The later development of a 2-site radioimmunometric assay allowed measurement of primarily intact
Study Participants
Participants were recruited from advertising in the local media and through a direct mail campaign. Exclusion characteristics consisted of any chronic illness, including hypertension, diabetes, or morbid obesity, any past history of illness or use of medication known to affect bone metabolism, any use of oral contraceptives or hormone replacement therapy, or a history of hysterectomy. After telephone screening, women were further excluded from the study because of abnormal results of blood
Predictors of PTH—Univariate and Multivariate Analysis
In Table 1, we provide descriptive statistics of all continuous variables and the univariate correlations with PTH. Mean PTH was significantly higher in black study subjects (38.9 ± 14.0 pg/mL) than in white study subjects (35.8 ± 12.6 pg/mL) (P < 0.02). Increasing PTH was also significantly correlated with increasing BMI (Fig. 1), increasing age (Fig. 2), decreasing dietary calcium, increasing serum creatinine, and decreasing 25-OHD (Fig. 3). The largest correlation was between PTH and BMI (r =
DISCUSSION
The current study confirms the manufacturer’s reference range for serum PTH with use of the Allegro radioimmunometric assay and establishes that its upper limit should not be lowered from 65 pg/mL. Our study participants were healthy volunteers recruited through a direct mail campaign. Volunteers with chronic illness, morbid obesity, hypertension, diabetes, thyroid disease, or osteoporosis were excluded from the study. They were further found to be healthy by a thorough history and physical
CONCLUSION
The data in this healthy female population suggest that the upper limit of the reference range for PTH with use of the intact Allegro radioimmunometric assay should not be lowered. Instead, in patients with normal serum calcium levels and PTH in the upper reference range, clinicians should consider whether they have higher PTH values because of increased body weight, advanced age, reduced renal function, low dietary calcium intake, or low serum 25-OHD levels. When these variables are not
ACKNOWLEDGMENT
This research was funded by the National Institute of Aging (RO1 AG15325), National Institutes of Health. We thank Sharon Sprintz, RT, and Jane Moore, RN, for their expertise and Audrey Gallo-Neglia for preparation of the manuscript.
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