What is parathyroid hormone (PTH)?

Parathyroid hormone (PTH) is a hormone that your parathyroid glands make and release to control the level of calcium in your blood, not your bones. Calcium is one of the most important and common minerals in your body. PTH also helps control the levels of phosphorus (a mineral) and vitamin D (a hormone) in your blood and bones.

Hormones are chemicals that coordinate different functions in your body by carrying messages through your blood to your organs, muscles and other tissues. These signals tell your body what to do and when to do it.

What are parathyroid glands?

Most people have four pea-sized parathyroid glands located behind their thyroid gland — the butterfly-shaped gland in your neck. Like your thyroid, your parathyroid glands are part of your endocrine system. Sometimes your parathyroid glands are located along your esophagus or in your chest. These are known as ectopic (in an abnormal place) parathyroid glands.

A gland is an organ that secretes (releases) certain substances for use inside your body or excretes substances out of your body. You have several different types of glands, including sweat glands, endocrine glands and salivary (spit) glands.

The main job of your parathyroid glands is to release parathyroid hormone (PTH). Sometimes, your parathyroid gland can release too little PTH, which results in low amounts of calcium in your blood (hypocalcemia), or too much PTH, resulting in high amounts of calcium in your blood (hypercalcemia). Both of these conditions can lead to serious health problems.

What is calcium and what does it do?

Calcium is one of the most important and common minerals in your body. Most of your calcium is stored in your bones, but you have and need it in your blood as well. The calcium in your blood has many important roles, including:

  • Helping your nerves work.
  • Helping to make your muscles squeeze together (contract) so you can move.
  • Helping your blood clot if you’re bleeding.
  • Helping your heart work properly.

How do vitamin D and phosphorus affect calcium levels in my blood?

Active vitamin D (calcitriol) helps to increase the amount of calcium your gut can absorb from the food you eat and release it into your bloodstream. Active vitamin D also prevents calcium loss from your kidneys. In your body, vitamin D (calcitriol) is actually a hormone rather than a vitamin.

Your skin mostly produces vitamin D from sun exposure — you also get some vitamin D from the food you eat. Your liver and kidneys transform that vitamin D into the active hormone, which is called calcitriol. Parathyroid hormone (PTH) increases the activity of the enzyme that produces active vitamin D.

The amount of phosphorous in your blood affects the calcium level in your blood. In your body, calcium and phosphorous react in opposite ways: As your blood calcium levels rise, phosphate levels drop — and vice versa.

What is the function of parathyroid hormone?

Your parathyroid gland releases parathyroid hormone (PTH) when your body detects low calcium levels in your blood. Parathyroid hormone regulates calcium levels in your blood by affecting the following parts of your body:

  • Bones: Parathyroid hormone stimulates the release of small amounts of calcium from your bones into your bloodstream.
  • Kidneys: Parathyroid hormone enables the production of active vitamin D (calcitriol) in your kidneys. PTH also signals your kidneys to retain calcium in your body rather than flushing it out through your urine.
  • Small intestine: Parathyroid hormone signals your small intestine to absorb more calcium from the food you eat.

Once your parathyroid glands release PTH when you have low blood calcium levels, the PTH is only active in your body for a few minutes. When your blood calcium levels rise, your parathyroid glands stop releasing PTH.

How does my body control parathyroid hormone levels?

Parathyroid hormone (PTH) levels are mainly controlled by a feedback loop of calcium levels in your blood to your parathyroid glands. In other words, low calcium levels in your blood stimulate parathyroid hormone release, whereas high calcium levels in your blood prevent your glands from releasing parathyroid hormone.

However, sometimes an issue with your parathyroid glands, such as a tumor or damage to the glands, can cause them to release too much or too little of PTH, regardless of the feedback loop.

What test checks parathyroid hormone levels?

Your healthcare provider can check your parathyroid hormone levels through a blood test. It involves using a needle to draw a blood sample from a vein in your arm. They then send the blood sample to a laboratory for testing.

What are normal parathyroid hormone levels?

Normal ranges for parathyroid hormone (PTH) levels can vary from lab to lab. Always reference the lab’s normal range on your blood test report.

In general, the normal range for the parathyroid hormone blood test known as “PTH, intact” is 15 to 65 picograms per milliliter (pg/mL). A picogram is one-trillionth of a gram.

If you need to get a parathyroid hormone level test, your healthcare provider will interpret your results and let you know if you need to get further testing.

What happens if parathyroid hormone levels are high?

When you have high levels of parathyroid hormone (PTH) in your blood, it causes you to have high levels of calcium in your blood (hypercalcemia) and low levels of phosphorous in your blood (hypophosphatemia), which cause certain symptoms and health conditions.

Symptoms of high parathyroid hormone levels

Since parathyroid hormone (PTH) mainly controls the amount of calcium in your blood, which has several important functions, the symptoms you’ll experience from high PTH levels are actually symptoms of high blood calcium levels. Symptoms of high blood calcium levels (hypercalcemia) include:

If you experience these symptoms of hypercalcemia, it’s important to contact your healthcare provider.

Causes of high parathyroid hormone levels

High parathyroid hormone (PTH) levels are primarily caused by hyperparathyroidism, which happens when your parathyroid glands are overactive and release too much PTH. In the United States, about 100,000 people develop hyperparathyroidism each year. It’s a treatable condition.

Causes of hyperparathyroidism include:

  • Parathyroid adenoma: A benign (noncancerous) growth (adenoma) forms on a single parathyroid gland and causes it to make excess PTH. This is the most common cause of hyperparathyroidism.
  • Hyperplasia: This happens when two or more of your parathyroid glands become enlarged and produce too much PTH.
  • Certain genetic conditions: Certain inherited conditions, such as multiple endocrine neoplasia type 1, can cause hyperparathyroidism.
  • Parathyroid cancer: Parathyroid cancer is rare, but it can cause hyperparathyroidism.

What happens if parathyroid hormones are low?

When you have low levels of parathyroid hormone (PTH) in your blood, it causes you to have low levels of calcium in your blood (hypocalcemia) and high levels of phosphorous in your blood (hyperphosphatemia), which cause certain symptoms and health conditions.

Symptoms of low parathyroid hormone levels

Since parathyroid hormone (PTH) mainly controls the amount of calcium in your blood, which has several important functions, the symptoms you’ll experience from low PTH levels are actually symptoms of low blood calcium levels. Symptoms of low blood calcium levels (hypocalcemia) include:

  • Tingling in your lips, fingers or feet.
  • Muscle cramps.
  • Dry skin and brittle fingernails.
  • “Brain fog” or confusion.
  • Seizures.
  • Irregular heart rhythm (arrhythmia).

If you’re experiencing these symptoms of hypocalcemia, it’s important to contact your healthcare provider.

When you have too much phosphorus in your blood due to low levels of PTH, it causes your body to pull calcium from your bones to try to keep your blood balanced. This can cause your bones to become weak and unhealthy, which puts you at a higher risk of bone fractures (breaks) and other issues.

Causes of low parathyroid hormone levels

Low parathyroid hormone (PTH) levels are primarily caused by hypoparathyroidism, which happens when your parathyroid glands are underactive and don’t release enough PTH. Hypoparathyroidism is rare and treatable.

Causes of hypoparathyroidism include:

  • Damage to your parathyroid glands: Approximately 75% of hypoparathyroidism cases are from accidental damage to your parathyroid glands from neck or thyroid surgery.
  • Certain genetic conditions: Genetic causes of hypoparathyroidism represent fewer than 10% of cases. The most common genetic cause is DiGeorge syndrome, a chromosomal genetic condition.
  • Certain autoimmune diseases: A disease called type 1 autoimmune polyglandular syndrome causes your immune system to attack your parathyroid glands, which causes chronic hypoparathyroidism. Addison’s disease and pernicious anemia can also cause hypoparathyroidism.
  • Low levels of magnesium: Your parathyroid glands need magnesium, a type of electrolyte in your blood, to function properly. Because of this, low levels of magnesium (hypomagnesemia) can cause hypoparathyroidism.

When should I see my doctor about my parathyroid hormone levels?

If you’re experiencing symptoms of hypercalcemia or hypocalcemia, it’s important to contact your healthcare provider.

A note from Cleveland Clinic

Parathyroid hormone is an important hormone that’s in charge of managing your blood calcium levels. If you’re experiencing symptoms of hypercalcemia or hypocalcemia, such as issues with your muscles and cognitive function, it’s important to contact your healthcare provider. They can run some simple tests to see if your parathyroid hormone levels are the culprit.

Last reviewed by a Cleveland Clinic medical professional on 12/21/2021.

References

  • Khan M, Jose A, Sharma S. Physiology, Parathyroid Hormone. (https://www.ncbi.nlm.nih.gov/books/NBK499940/) [Updated Sep 27, 2021]. In: StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing; 2021. Accessed 11/1/2021.
  • Lab Tests Online. Parathyroid Hormone (PTH). (https://labtestsonline.org/tests/parathyroid-hormone-pth) Accessed 11/1/2021.
  • Society for Endocrinology. Parathyroid Hormone. (https://www.yourhormones.info/hormones/parathyroid-hormone/) Accessed 11/1/2021.
  • Society for Endocrinology. Vitamin D. (https://www.yourhormones.info/hormones/vitamin-d/) Accessed 11/1/2021.

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