Pth
Parathyroid hormone, which regulates calcium and phosphate. Interpreted together with calcium and vitamin D.
Typical reference range
| Range | Unit |
|---|---|
| 1.6–6.9 | pmol/l |
What Pth measures
PTH (parathyroid hormone) is made by the four small parathyroid glands in the neck. It is the main regulator of blood calcium, and, together with vitamin D, it also helps manage phosphate and bone turnover.
Because of this, PTH is almost always read together with calcium, and often alongside vitamin D and phosphate. The meaning of a single PTH value depends heavily on what calcium is doing at the same moment, so the two are best interpreted as a pair rather than in isolation.
- Regulates blood calcium as its main job
- Works with vitamin D on phosphate and bone
- Interpreted in the context of calcium, not alone
A clinician looks at the whole picture rather than one number.
What a high Pth can mean
A high PTH result can point in different directions depending on what calcium is doing at the same time, which is why the two are paired.
- With high calcium, a high PTH can suggest primary hyperparathyroidism, where a gland is overactive and driving calcium up.
- With low or normal calcium, a high PTH is often the body responding appropriately to low calcium or low vitamin D. This pattern is sometimes called secondary hyperparathyroidism.
- It can also reflect the effects of kidney disease on calcium and phosphate balance.
Because these possibilities look similar on paper, the calcium value is the key companion to PTH here. Clinician interpretation is essential, and follow-up may include repeat testing plus vitamin D, phosphate, and kidney measures. Discuss any high result with a clinician.
What a low Pth can mean
A low PTH result is also read alongside calcium, since the same number can mean different things.
- With high calcium, a low PTH can suggest the calcium is coming from a source outside the parathyroid glands, so the glands appropriately switch themselves off.
- With low calcium, a low PTH can suggest underactive parathyroid glands (hypoparathyroidism). This sometimes follows neck or thyroid surgery, or relates to a magnesium disturbance affecting how the glands work.
As with a high result, the calcium value is the essential companion to a low PTH, and phosphate, vitamin D, and magnesium may be reviewed too. A single reading rarely tells the whole story on its own, so it is best to discuss a low PTH with a clinician who can interpret it in context.
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