Parathyroid hormone (PTH) is secreted in response to small changes in circulating calcium concentration allowing tightly regulated homeostasis.
Autonomous secretion of PTH, as characterised by primary hyperparathyroidism, leads to hypercalcaemia and potential end organ damage (osteoporosis and renal calculi). An association has been noted with cardiovascular disease although causality remains unclear (1).
Over the last decade, a new entity has been identified characterised by high PTH yet normal calcium and vitamin D. The aetiology and pathological consequences of this remains uncertain.
Aim
To describe the normal reference range for PTH by age.
Methods
Data from 445 female participants within the Barwon Statistical Division (as detailed in the Geelong Osteoporosis Study) was extracted for PTH, 25-hydroxy vitamin D (25(OH)D) and calcium concentrations. Analysis of serum 25(OH)D was performed using equilibrium radioimmunoassay following extraction using acetonitrile (Incstar, Stillwater, MN, USA). Intact PTH concentration was anlysed using chemiluminescent enzyme assay (Immulite; Diagnostic Products Corp., Los Angeles, CA, USA). Participants with calcium and 25(OH)D outside normal reference range (calcium 2.15–2.55 mmol/L; 25(OH)D ≥ 50 nmol/L) were excluded.
After log transformation, mean values according to decades of age were analysed using linear regression (Graph Pad Prism 5). Reference range for each decade was specified as 95% confidence interval.
Results
PTH increased with age (p<0.05) whilst a trend was observed for decreasing 25(OH)D (p=0.05). No significant correlation was observed between age and calcium.
PTH reference ranges are shown in the table:
|
Number of participants |
87 |
109 |
71 |
53 |
47 |
47 |
41 |
|
|
Age range (years) |
20-29 |
30-39 |
40-49 |
50-59 |
60-69 |
70-79 |
80-90 |
|
|
Ref range (pmol/L) |
Lower limit |
0.63 |
1.4 |
1.6 |
2 |
2 |
3.1 |
1.7 |
|
Upper limit |
6.9 |
7.2 |
6.6 |
8.3 |
7.6 |
8.7 |
18.5 |
Conclusion
Within this cohort, PTH reference range varies according to age, possibly because of down regulated activation and altered metabolism of Vitamin D.