Parathormone: What is it? Function, Tests, Associated Diseases and Treatments

Also called parathyroid hormone or PTH, it is produced by the parathyroid glands.

Most people have 4 pea-sized parathyroid glands embedded in the back of the thyroid gland , but variations in their location and number sometimes occur.

PTH regulates the levels of calcium, phosphorus and magnesium in the blood.

Because calcium balance plays a critical role in many bodily functions, including muscle movement and nerve impulses, calcium levels are tightly controlled to stay within a narrow concentration range in the blood.

Function

The main function of PTH is to increase calcium levels when they are too low. It activates the release of calcium from the bones into the blood, decreases the loss of calcium in the urine and increases the absorption of calcium from food.

Measuring parathyroid hormone levels can help find the cause of inadequate calcium levels and can be used to monitor the progression of some diseases.

Parathyroid hormone increases calcium in the blood:

Through the bones

The bones act as reservoirs for calcium, releasing calcium into the bloodstream when blood levels are low and absorbing calcium when they are high. PTH tells bone cells what action is necessary.

The parathyroid glands have calcium sensors. When calcium is low, the glands release more PTH. High PTH levels signal the bones to release more calcium into the blood.

When calcium levels in the blood are high, the parathyroid glands release less PTH. Low PTH levels signal the bones to take calcium from the blood.

Through the kidneys

As the blood is filtered through the kidneys, some molecules are returned to the blood and others are eliminated from the body in the urine. Parathyroid hormone influences the net balance of how much calcium and phosphorus is removed and how much is retained during that process.

When PTH is high, the kidneys absorb less calcium. When PTH is low, more calcium is excreted in the urine, lowering the concentration of calcium in the blood.

Through the intestines

Parathyroid hormone activates the kidneys to convert vitamin D from its inactive form to its active form (1,25-dihydroxyvitamin D or calcitriol). In its active form, vitamin D increases the absorption of calcium in the intestines.

Higher levels of PTH lead to an increase in active vitamin D, which leads to an increase in intestinal absorption of calcium, which leads to a higher concentration of calcium in the blood.

Parathyroid hormone and calcitonin

Calcitonin is produced in the thyroid gland and helps maintain blood levels of calcium. If calcium levels are too high, calcitonin lowers them.

Calcitonin is produced in response to high levels of calcium in the blood.

Basically, calcitonin has the opposite effect to PTH. Both hormones are responsible for maintaining healthy levels of calcium in the blood.

Parathyroid hormone test

The level of parathyroid hormone can be measured by a blood test, and typically ranges from 10 to 65 ng / L.

Different labs may use different test methods, so normal ranges may vary.

Therefore, although laboratories will provide the range of normal values ​​for their methodology, direct comparison of values ​​from different laboratories may be inappropriate.

Normal biological variation in parathyroid hormone levels

Normally, PTH is released at low levels throughout the day and at pulses of higher levels a few times per hour.

An analysis of 3.6 million blood tests showed that vitamin D and PTH levels vary seasonally. When vitamin D levels drop, PTH levels rise, after about 4 weeks of vitamin D levels.

On average, men’s vitamin D levels are lower and PTH levels are higher than women’s levels.

Parathyroid hormone levels can also increase during and after exercise, depending on its duration and intensity.

Parathyroid hormone levels may differ between populations

In one study, Mexicans and African Americans were found to have higher PTH than whites. However, both white and black Americans were found to have a higher incidence of primary hyperparathyroidism (abnormally high PTH) than Mexican-Americans in another study.

Additionally, vitamin D deficiencies affected PTH levels differently in African Americans than in the other two groups.

While PTH levels continued to decline with vitamin D levels greater than 20 ng / ml in whites and Mexican Americans, they did not follow the same pattern with vitamin D greater than 20 ng / ml in blacks.

Parathyroid hormone levels are higher with obesity

As total body fat increases, parathyroid hormone levels increase. The effect of obesity on PTH levels is seen even when controlling for the decrease in vitamin D levels associated with more body fat.

Increased waist size in women carries an increased risk of developing hyperparathyroidism (abnormally high PTH).

One study found that both leptin and PTH levels increase with increasing body mass. However, only in people with higher levels of leptin (greater than 10 ng / ml) was the decrease in vitamin D associated with an increase in PTH.

Leptin appears to affect PTH levels, and both leptin and PTH regulate the conversion of vitamin D to its active form.

High parathyroid hormone (hyperparathyroidism)

Hyperparathyroidism is the condition of abnormally high levels of parathyroid hormone in the blood.

High levels of parathyroid hormone have been associated with the following symptoms and health problems:

  • Renal disease.
  • Kidney stones
  • Osteoporosis.
  • Pain in the bones, joints, or muscles.
  • High blood pressure.
  • Hardening of the arteries (arteriosclerosis).
  • Heart-related disorders.
  • Colon polyps (adenomas).
  • Inflammation.
  • Fatigue.
  • Depression.
  • Brain fog.
  • Cystic fibrosis.
  • Liver disease.
  • Primary aldosteronism (high levels of aldosterone).

Causes of abnormally high parathyroid hormone levels

Dietary deficiencies

Abnormally low levels of calcium in the blood increase parathyroid hormone levels. Dietary deficiencies in calcium or vitamin D are the most direct causes of low blood calcium levels.

Supplementation with vitamin D and K, as well as calcium, can lower PTH levels and improve bone strength in women with osteoporosis.

Health problems that cause low calcium levels

Chronic kidney disease can affect kidney function, which can decrease the amount of calcium reabsorbed by the kidneys during blood filtration. The resulting low blood calcium levels indicate that the parathyroid glands release more PTH, causing abnormally high levels of the hormone in the blood.

Primary aldosteronism (high levels of aldosterone) can cause elevated PTH levels. High aldosterone levels cause the kidneys to release more calcium into the urine, lower blood calcium levels, and trigger the parathyroid glands to release more PTH.

Poor absorption of nutrients by the intestines can lead to low levels of calcium in the blood, which could trigger more release of PTH.

Malfunction of the parathyroid gland

The most common problem with the parathyroid glands is the excessive release of PTH despite normal or even high levels of calcium in the blood. This is known as primary hyperparathyroidism.

Parathyroid gland dysfunctions are most commonly caused by a benign tumor (adenoma). The second most common cause is increased cell growth in the parathyroid gland (hyperplasia). Cancer of the parathyroid glands is responsible for about 1% of cases.

Some drugs

High levels of parathyroid hormone can be a side effect of high-dose lithium treatment for bipolar disorder.

Furosemide, a diuretic used to treat fluid build-up and high blood pressure, increases PTH levels.

Genes

Increased PTH levels are associated with genetic variations in or near genes involved in vitamin D production and calcium and phosphate transport, including these SNPs:

  • rs6127099 (upstream of CYP24A1).
  • rs4074995 (within RGS14).
  • rs219779 (adjacent to CLDN14).
  • rs4443100 (near RTDR1).
  • rs73186030 (cerca de CASR).

Hyperparathyroidism has also been associated with mutations in:

  • CDC73.
  • GCM2.

How to lower parathyroid hormone levels

If high PTH levels are caused by nutritional deficiencies, levels can return to normal by taking calcium and vitamin D supplements.

However, high PTH is most often caused by parathyroid gland tumors or chronic kidney disease. In that case, the underlying condition needs treatment.

Ways to lower PTH levels or reduce the risk of developing hyperparathyroidism include:

  • Calcium supplements.
  • Vitamin D supplements and sun exposure.
  • Weightloss.
  • Exercise.
  • Reduce inflammation.
  • Low parathyroid hormone (hypoparathyroidism)

Hypoparathyroidism is the condition of low or inappropriately normal levels of parathyroid hormone in the blood.

If calcium levels in the blood are low, the parathyroid glands normally release extra PTH. Therefore, PTH levels in the normal range are considered inappropriate when calcium levels in the blood remain low.

Hypoparathyroidism generally leads to low calcium levels and high phosphate content in the blood.

Causes of low parathyroid hormone

Surgery

About 75% of hypoparathyroidism cases are the result of neck surgery, such as removal of the thyroid or parathyroid glands.

Hypoparathyroidism resulting from surgery can cause a rapid decrease in calcium levels that requires immediate attention. In general, postsurgical hypoparathyroidism is defined as having blood calcium less than 8.0 mg / dL and PTH less than 15 ng / L.

About 75% of hypoparathyroidism cases after surgery are transient (temporary) and PTH levels return to normal in less than 6 months.

Low levels of vitamin D before surgery can increase the risk of postsurgical hypoparathyroidism.

To minimize risk, it is recommended that blood levels of vitamin D before surgery be at least 20 ng / dL.

Magnesium imbalance

High and very low levels of magnesium decrease PTH levels in the blood.

Autoimmune disorders

Hypoparathyroidism often occurs as part of autoimmune poliendocrine syndrome, which is a genetic disorder.

In addition to that, autoantibodies against some parathyroid-related proteins have been identified in patients with hypoparathyroidism with no other known causes, such as calcium sensing receptor (CaSR) and leucine-rich repeat protein NACHT 5 (NALP5).

Some drugs

Digoxin, which is used to treat atrial fibrillation, lowers parathyroid hormone levels.

Genes

These genetic disorders and their related genes are associated with hypoparathyroidism:

  • Autoimmune poliendocrinopathy syndrome type 1 (AIRE).
  • DiGeorge syndrome types 1 (TBX1) and 2 (NEBL).
  • Hypoparathyroidism-deafness-renal dysplasia syndrome (GATA3).
  • Kenny-Caffey syndrome type 1 (TBCE) and 2 (FAM111A).
  • Síndrome de CHARGE ( CHD7 , SEMA3E ).
  • Bartter syndrome, type 5 (CASR).

Mutations in these genes have been associated with hypoparathyroidism:

  • GCM2.
  • PTH (parathyroid hormone gene).
  • FHL1.

Hypoparathyroidism treatment

Hypoparathyroidism is most often treated with supplements of calcium (1,000 to 9,000 mg / day) and vitamin D (0.25 to 2.0 ug / day of calcitriol). The goal is to keep your blood calcium levels between 8.0 and 9.0 mg / dl and avoid high levels of calcium in your urine.

A synthetic parathyroid hormone (Natpara) was approved by the FDA as a treatment in 2015. However, the long-term complications of its use are still being evaluated.

Health problems associated with hypoparathyroidism

Low calcium levels caused by hypoparathyroidism commonly cause problems in the muscles and nervous system.

High calcium intake used to treat low PTH levels can cause kidney stones and increase the risk of developing chronic kidney disease.

Bone mass density is usually higher in patients with chronic hypothyroidism. Whether that is due to treatment with calcium and vitamin D supplements or low PTH levels that reduce bone restructuring, or if it is a combination of both, is unclear.

Many patients with hypoparathyroidism report a reduced quality of life, including fatigue, depression, anxiety, and cognitive difficulties.

Health problems associated with hypoparathyroidism can be the result of low calcium levels or treatment with calcium supplements. They include:

  • Fatigue.
  • Muscle cramps.
  • Heart disease.
  • Seizures
  • Psychiatric disorders.
  • Infections that require hospitalization.
  • Kidney disorders.
  • Waterfalls.
  • Bronchial spasms
  • Bone fractures in arms.
  • Calcium deposits in the brain (calcification of the basal ganglia).

How to Increase Parathyroid Hormone Levels

Make sure your magnesium levels are balanced. If they are on the low end, you may want to take magnesium supplements.

Using parathyroid hormone to treat osteoporosis

Because parathyroid hormone is a key driver of bone formation, it is an important factor in many bone disorders.

A synthetic parathyroid hormone analog (teriparatide) is used to treat severe osteoporosis. It is effective in building bone when given in low, intermittent doses.

In 2017, the FDA approved another parathyroid hormone-like drug, abaloparatide, to treat severe osteoporosis.