What the parathyroid hormone (PTH) test shows
Parathyroid hormone comes from four small glands behind the thyroid and is the body’s main controller of blood calcium. When calcium dips, the glands release PTH, which raises it by freeing calcium from bone, making the kidneys keep calcium while flushing out phosphate, and switching on active vitamin D to absorb more from food. As calcium recovers, PTH switches off — the negative-feedback loop StatPearls calls the core of calcium balance.
Because of that loop, a PTH result means little on its own: it must be read next to calcium, since the same number can be normal, too high or too low depending on what calcium is doing. MedlinePlus notes a calcium test is almost always ordered with it.
It also differs from its neighbours. The standard assay is “intact” PTH (iPTH), the whole active hormone; calcitonin, from the thyroid, lowers calcium but matters little in humans; and vitamin D is PTH’s partner, since PTH activates it and low vitamin D is a common reason PTH runs high.
Parathyroid hormone normal range
Intact PTH is reported in pg/mL, numerically identical to the SI unit ng/L (1 pg/mL = 1 ng/L), so US and European reports with the same figure mean the same thing. A widely used adult band is roughly 10–65 pg/mL, though exact numbers depend on the assay and lab.
| Group | Orientation, pg/mL (= ng/L) |
|---|---|
| Adults (typical intact-PTH assay) | ~10–65 |
| Older adults (60+) | often in the upper half |
| Children and teenagers | age-specific — use your lab’s range |
| Any age | interpret only with a same-day calcium |
One idea matters more than the number: PTH is judged against calcium, not the range alone. MedlinePlus notes that a PTH inside the “normal” band is still inappropriate — and abnormal — if calcium is high at the same time. Reference ranges depend on the lab, sex and age — always read your result against your own report.
Why parathyroid hormone is high
A high PTH is common, and calcium tells you which of two very different situations you are in.
- High PTH with high calcium — primary hyperparathyroidism. The glands are overactive on their own, usually a single benign adenoma (about 80–85% of cases), per StatPearls. The commonest cause of a high calcium on routine bloods, it is often silent but can cause kidney stones, thinning bones and fatigue.
- High PTH with low or normal calcium — secondary hyperparathyroidism. The glands work correctly, defending calcium against something pulling it down: most often vitamin D deficiency, then chronic kidney disease, where failing kidneys retain phosphate and cannot activate vitamin D, as StatPearls and the KDIGO guidelines describe. Low calcium intake and malabsorption act the same way.
When is it urgent? The PTH is not the emergency — the calcium is. A markedly high calcium (above ~14 mg/dL) with confusion, vomiting or extreme thirst is a hypercalcemic crisis needing same-day care.
Why parathyroid hormone is low
A low PTH is less common but often more pressing, because it appears with a falling calcium the glands can no longer defend. Again, calcium sets the meaning.
- Low PTH with low calcium — hypoparathyroidism. The glands cannot make enough hormone. By far the commonest cause is neck surgery — thyroid or parathyroid operations that damage or remove the glands — which StatPearls links to about three-quarters of cases; it may be temporary or permanent. Autoimmune damage, absent glands or radiation cause the rest.
- A magnesium problem. Very low, or very high, blood magnesium stops the glands releasing PTH — a functional hypoparathyroidism that corrects only once magnesium is put right, so magnesium is checked in any unexplained low calcium.
- Low PTH with high calcium — the correct response. When calcium is high from something other than the parathyroids — a cancer, too much vitamin D or sarcoidosis — healthy glands switch PTH off, so a low PTH here is reassuring and points the search outward.
When is it urgent? Falling calcium causes tingling around the mouth and fingers, muscle cramps and, if severe, spasms of the hands and feet or seizures — especially soon after neck surgery, these need urgent assessment.
What to test alongside
PTH is one leg of a small calcium-metabolism panel and is rarely read alone:
- Calcium (corrected for albumin, or ionized) — the number PTH is always read against.
- Phosphate — moves opposite to calcium: high in kidney disease and hypoparathyroidism, low in primary hyperparathyroidism.
- Magnesium — too little or too much shuts PTH release off.
- Vitamin D — deficiency is the leading cause of a raised PTH.
- Creatinine — flags the kidney disease behind most secondary hyperparathyroidism.
- TSH and free T4 — thyroid checks from the same neck region, since thyroid surgery is the top cause of a low PTH.
- Estradiol and testosterone — sex hormones whose decline, like excess PTH, drives bone loss in an osteoporosis work-up.
What to do about an abnormal result
- Don’t self-treat. Do not start or stop calcium or vitamin D on your own to “correct” a number — the right move depends on the calcium-PTH pattern, and guessing can make things worse.
- Get the pair, then repeat it. An abnormal PTH means little without a same-day calcium, and one odd result is usually rechecked — often with vitamin D, phosphate and magnesium — before any label sticks.
- For high PTH: the doctor sorts high calcium (primary hyperparathyroidism, possibly an endocrine surgeon) from low or normal calcium (secondary — usually vitamin D deficiency or kidney disease, managed medically).
- For low PTH: the focus is protecting calcium, especially soon after neck surgery; lasting hypoparathyroidism is managed by an endocrinologist with active vitamin D and calcium.
- See your GP or primary-care physician first. They order the calcium-PTH pair and decide whether an endocrinologist, endocrine surgeon or kidney specialist is the right next stop.
Mini-FAQ
Why is calcium always tested together with PTH?
PTH only makes sense next to calcium, because the parathyroid glands’ whole job is to hold calcium steady. The same PTH number can be normal, too high or too low depending on whether calcium is high, normal or low, so labs read the pair together.
What is a normal PTH level?
Most labs put intact PTH around 10–65 pg/mL (10–65 ng/L), but the exact range and assay vary. A value inside the range can still be inappropriate — a normal PTH is effectively too high if your calcium is elevated.
What does a high PTH usually mean?
With high calcium, it usually means primary hyperparathyroidism — most often a single benign parathyroid tumour. With low or normal calcium, a high PTH is usually a healthy reaction to vitamin D deficiency or kidney disease (secondary hyperparathyroidism).
What does a low PTH mean?
If calcium is also low, the glands are underactive (hypoparathyroidism), most often after thyroid or neck surgery. If calcium is high, a low PTH is the correct response to calcium arriving from another source, such as a cancer or too much vitamin D.
Is an abnormal PTH an emergency?
The PTH number itself is rarely the emergency — the calcium is. Very high calcium (confusion, vomiting, extreme thirst) or very low calcium (numbness, tingling, cramps or spasms) needs same-day care.
