Does aging alone result in increased PTH levels? (#70)
Background: It is known that parathyroid hormone (PTH) levels increase with age, but it is uncertain whether this is independent of age-related changes in renal function, calcium balance and vitamin D status (1, 2). This is important because elevated PTH is associated with adverse outcomes in epidemiological studies (3, 4).
Aim: The aim of this study was to examine whether age alone is an independent predictor of PTH after correcting for variables known to alter PTH levels (calcium, vitamin D and renal function).
Method: We undertook a retrospective cross-sectional analysis from two pathology laboratories of 38,000 fasting metabolic bone studies, a standardised panel which includes measurement of plasma ionised Calcium (iCa), PTH, creatinine, 25(OH)vitamin D (25(OH)D) collected after an overnight fast and before taking any medications. Estimated glomerular filtration rate (eGFR) was calculated using the MDRD equation. We excluded subjects with ionised hypercalcaemia, 25(OH)D levels below <25nmol/L or eGFR <30 ml/min/m^2 and those taking antiresorptive therapy. The data were analysed by 20 year age bands (20-39, 40-59, 60-79, 80+). The relationship between age group and PTH was evaluated by linear regression analysis, with eGFR, iCa and 25(OH)D levels as covariates.
Results: The mean PTH increased steadily across age groups from 20-39 yrs upwards (Table). After adjustment for eGFR, iCa and 25(OH)D, there were significant differences between all age group pairs (all p<0.0001; adjusted significance level is α'=0.0083).
Conclusion: This study demonstrated an age related increase in PTH whilst controlling for confounding factors. In view of our findings, adoption of age-specific PTH reference intervals may need to be considered.
- Arabi A, Baddoura R, El-Rassi R, Fuleihan GE-H. Age but not gender modulates the relationship between PTH and vitamin D. Bone 2010; 47:408-412.
- Need AG, O'Loughlin PD, Morris HA, Horowitz M, Nordin BEC. The effects of age and other variables on serum parathyroid hormone in postmenopausal women attending an osteoporosis center. J Clin Endocrinol Metab 2004; 89:1646-1649.
- Sambrook PN, Chen JS, March LM, Cameron ID, Cumming RG, Lord SR, Schwarz J, Seibel MJ. Serum parathyroid hormone is associated with increased mortality independent of 25-Hydroxy vitamin D status, bone mass, and renal function in the frail and very old: A cohort study. J Clin Endocrinol Metab 2004; 89:5477-5481.
- Bjorkman MP, Sorva AJ, Tilvis RS. Elevated serum parathyroid hormone predicts impaired survival prognosis in a general aged population. Eur J Endocrinol 2008; 42:267-270.