Parathyroid hormone (PTH) is the hormone released by the four parathyroid glands in the neck to keep blood calcium inside a narrow range, by pulling calcium out of bone, holding onto it in the kidney and switching on the active form of vitamin D. It is the body’s main minute-to-minute calcium thermostat. A PTH result is close to meaningless on its own: it is read together with calcium, because the same number can be normal, alarming or reassuring depending on what calcium is doing at the same time.
What it measures
The blood test almost always reports intact PTH – the whole, biologically active molecule – from a routine venous draw. The hormone has a short half-life and is secreted in pulses, so labs often ask for a morning sample and a calcium level drawn at the same time. Some centers also measure PTH during surgery to confirm an overactive gland has been removed.
The glands sense free calcium directly. When it falls, PTH rises within minutes: it frees calcium from bone, reduces calcium loss in the urine, and tells the kidney to convert stored vitamin D into its active form so the gut absorbs more. When calcium rises, PTH is switched off. A full reference on the test and its interpretation is Parathyroid hormone (PTH), and the partner value it is always read beside is Calcium (total and ionized).
Typical values
Many labs report the intact PTH interval as roughly 10-65 pg/mL (about 1-7 pmol/L), but this is one of the most assay-dependent tests in routine use. Ranges differ between analyzers and run higher with age and reduced kidney function. Use the interval printed on your own report, and compare results over time only within the same laboratory.
The pattern that matters is the pairing with calcium:
| Calcium | PTH | What that pattern usually points to |
|---|---|---|
| High | High, or normal when it should be suppressed | Primary hyperparathyroidism – one gland acting on its own |
| High | Low | A cause outside the parathyroids, including cancer-related high calcium |
| Low or low-normal | High | Secondary hyperparathyroidism – the glands compensating for vitamin D deficiency, poor calcium intake or chronic kidney disease |
| Low | Low | Hypoparathyroidism, often after neck surgery, sometimes with severe magnesium depletion |
Why it matters for longevity
PTH matters because of what chronic elevation does to the skeleton and the vasculature. Sustained high PTH keeps bone turnover switched on, and primary hyperparathyroidism is associated with lower bone density, fractures and kidney stones – a condition that is diagnosable and surgically treatable, which is why an unexplained high calcium should never be filed away. In chronic kidney disease, secondary hyperparathyroidism is part of the mineral and bone disorder linked with vascular calcification and higher cardiovascular mortality.
In older adults without overt disease, higher PTH has been associated in observational studies with fracture risk and cardiovascular events. Association is not causation: high PTH often marks low vitamin D, poor kidney function or low calcium intake, and those may be doing the damage.
What changes it
The largest correctable driver of a mildly high PTH is vitamin D deficiency; correcting it, when it is genuinely low, usually brings PTH down, and Vitamin D is measured alongside PTH for exactly that reason. Adequate dietary calcium works the same way – a low intake keeps the glands working harder than they need to. Declining kidney function raises PTH, as does severe magnesium depletion, which can paradoxically block PTH release and leave calcium low and stubborn. Lithium and thiazide diuretics can nudge calcium and PTH upward.
Nothing you do at the gym or the dinner table fixes a single overactive gland: that is an endocrine problem, assessed with imaging and often resolved by surgery. What you control is the background – vitamin D status, calcium intake, kidney health and the medication list.
Related reading
- How to Strengthen Bones and Prevent Osteoporosis
- Vitamin D and Longevity: Who Needs a Supplement
- Which Blood Tests Reflect Aging and How to Read Them
- Calcium
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.