Parathyroid hormone (PTH)
Hormone from the parathyroid glands that controls the calcium level in the blood
Also known as
Definition
Parathyroid hormone (PTH) is made by the four small parathyroid glands in the neck. When the calcium level in the blood drops, they release PTH: it tells the bones to release calcium, helps the intestines absorb calcium from food and makes the kidneys lose less calcium through urine. PTH also affects phosphate and vitamin D. Because PTH follows the calcium level, the result is usually read together with calcium.
| Parameter | Value |
|---|---|
| Unit | pg/mL (ng/L) |
| Reference Range | Adults: typically 10–65 pg/mL (equal to 10–65 ng/L). Labs may differ and some use other measuring methods; the reference range in your own report is what counts. Discuss your results with your doctor. |
Agree on your personal target range with your doctor.
1 pg/mL equals exactly 1 ng/L. Some labs report PTH in pmol/L: 1 pg/mL equals about 0.106 pmol/L (molar mass of intact PTH roughly 9.4 kDa), so 10–65 pg/mL is about 1.1–6.9 pmol/L.
↓ What a low value means
If PTH is low and calcium is also low, it can mean the parathyroid glands are not making enough hormone (hypoparathyroidism). Possible associations include damage from neck surgery or radiation, certain autoimmune disorders, rare genetic causes such as DiGeorge syndrome, serious illness and a low magnesium level. MedlinePlus also lists long-term very high intake of calcium or vitamin D from supplements or calcium-containing antacids, cancers that have spread to the bone and release calcium there, and sarcoidosis or tuberculosis, usually when these raise the calcium level. Interpretation is up to your doctor.
↑ What a high value means
A high PTH level is called hyperparathyroidism; which type it may be depends mainly on the calcium level. If calcium is also high, it is called primary hyperparathyroidism; the most common cause is a benign growth in one parathyroid gland (adenoma), less often enlarged glands, inherited conditions or, very rarely, cancer. If calcium is low instead, it is called secondary hyperparathyroidism: the glands make more PTH to raise calcium. Possible associations include a lack of vitamin D, phosphate or magnesium, too little calcium in the diet, absorption problems in the gut and kidney disease. Rarely, pregnancy or breastfeeding may play a role, as may the body not responding to PTH (pseudohypoparathyroidism). Interpretation is up to your doctor.
When to test
The test is usually ordered after an abnormal calcium result, for symptoms that may fit too much or too little calcium, to clarify a low phosphate result, for severe unexplained osteoporosis, for chronic kidney disease and to monitor known parathyroid disorders. Usually no special preparation is needed; some practices ask you to fast or to come at a certain time of day.
Frequently asked questions
Why is PTH almost always measured together with calcium? +
Because PTH follows the calcium level: when calcium drops, the parathyroid glands release more PTH; once calcium is back in the normal range, PTH falls. Only comparing both values shows whether the glands are responding appropriately. According to MedlinePlus, even a PTH value within the reference range can be inappropriate if calcium is high at the same time.
What is the difference between primary and secondary hyperparathyroidism? +
In both, PTH is high. In the primary type, calcium is also high, and the cause usually lies in the parathyroid glands themselves. In the secondary type, calcium is low: the glands work correctly and make more PTH because a cause outside them, such as vitamin D deficiency or kidney disease, keeps calcium low. Your doctor determines which type applies.
Why should PTH be measured at the same lab when possible? +
Labs partly use different measuring methods and sample types, so reference ranges differ slightly. MedlinePlus recommends using the same lab for repeat tests when possible so that results can be compared reliably over time.
How is vitamin D connected to PTH? +
Besides calcium and phosphate, PTH also affects the vitamin D level. In turn, vitamin D deficiency can be associated with low calcium and high PTH. That is why calcium, phosphate and vitamin D are often measured together with PTH. Discuss the combination of your results with your doctor.
Parathyroid hormone (PTH)
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.