Parathyroid hormone

General What "and Why is it measuredNormal valuesHigh parathyroid hormone - CausesLow parathyroid hormone - Causes How to measure Preparation Interpretation of results , located in the neck, near the thyroid.
Its main role is to keep the calcium concentration in the bloodstream constant (called calcemia).
Normally, when the calcium levels in the blood decrease, the parathyroid glands release PTH, which causes increases in calcium by acting in three different ways:

• Promotes the release of calcium from the bones into the bloodstream;
• Promotes intestinal absorption of calcium (through vitamin D);
• It acts on the kidneys by decreasing the elimination of calcium in the urine.

As calcium levels rise in the blood, PTH decreases.
The doctor may prescribe the test to measure the parathyroid hormone in the blood when he wishes to evaluate the functioning of the parathyroid glands, or in the case of abnormal levels of calcium in the blood, both in excess (hypercalcemia) and in defect (hypocalcemia).

The test is also used to establish whether the cause of an altered calcemia is deriving from a parathyroid disorder or from a kidney disease.

. It is secreted by the parathyroid glands, four endocrine glands located in the neck, on the dorsal aspect of the thyroid.
Parathyroid hormone, together with calcitonin, is used for the homeostasis of calcium and phosphorus ions. These two minerals, in addition to being the main constituents of bones and teeth, allow muscle contraction, transmission of nerve impulses, blood coagulation and the normal course of numerous metabolic reactions. It is therefore essential that their concentration remains relatively constant throughout the day.

CALCEMIA PHOSPHATEMIA (blood calcium concentration) (concentration of inorganic phosphate in the blood) Normal values: 10 mg / 100 ml Normal values: 5 mg / 100 ml   PARATORMONE, normal values: 10-65 pg / mL - 10-65 ng / L

Evaluation of PTH levels in the blood is done to confirm the suspicion of hyperparathyroidism or in the presence of significant abnormalities of calcium

To keep these values ​​in balance, the body mainly relies on two hormones:

• The parathyroid hormone, which performs a "hypercalcemizing action;
• Calcitonin, which plays the opposite role.

1,25- (OH) 2-cholecalciferol or calcitriol, which represents the active form of vitamin D, also intervenes in the "homeostasis of calcium."

Actions of the parathyroid hormone

At the level of the bones, the parathyroid hormone stimulates the mobilization of calcium by direct and indirect ways.
In the first case it intervenes in the first person, positively modulating the activity of osteoclasts (large cells that have the function of eroding and renewing the bone matrix). Since the bone tissue is rich in calcium ions, its catabolism favors the increase of calcemia.
At the renal level, parathyroid hormone increases the excretion of phosphate ions in the urine, decreasing the concentration of the mineral in the blood. To balance the situation, the organism draws phosphate from the bones, where it is deposited in the form of hydroxyapatite Ca5 (PO4) 3 (OH). Observing the molecular formula of this mineral, we understand that if on the one hand its degradation leads to an increase in phosphorus (P), on the other it also increases the release of calcium (Ca2 +).
In the intestine, thanks to the help of calcitriol (active form of vitamin D), the parathyroid hormone stimulates the absorption of calcium. In the kidney, the same hormone stimulates the activation of the aforementioned vitamin.
In addition to promoting the excretion of phosphate in the urine, the parathyroid hormone has a positive effect on the reabsorption of calcium.

Parathyroid hormone is a hypercalcemic hormone that acts at three levels (renal, intestinal and bone):

1. increasing the renal reabsorption of Ca2 +
   
2. increasing the renal elimination of phosphorus
   
3. stimulating the formation of Vitamin D3 from D2 (kidney)
   
4. increasing bone degradation
   
5. increasing intestinal absorption of calcium

The decrease in calcemia represents a strong stimulus on the secretion of parathyroid hormone and, in parallel, inhibits the release of its antagonist (calcitonin). Similarly, as soon as the calcium concentration in the blood exceeds normal values, the secretion of parathyroid hormone is inhibited.
This fine regulation mechanism keeps plasma calcium levels within fairly narrow limits; when this mechanism goes haywire, the calcemia undergoes important changes. This is the case, for example, of hyper and hypoparathyroidism, which are accompanied, respectively, by hyper and hypocalcemia.

, for which a malfunction of the parathyroid glands is suspected.
PTH is also required in the monitoring of patients with chronic kidney disease or undergoing dialysis.

When is the exam prescribed?

Doctors prescribe parathyroid hormone testing when blood calcium levels are higher (hypercalcemia) or lower (hypocalcemia) than normal, to identify the source of the imbalances and make a differential diagnosis between parathyroid and non-parathyroid causes.

The parathyroid test is indicated to evaluate the functioning of the parathyroid glands or when there is a suspicion of kidney disease.

In addition, PTH is checked regularly in patients with diseases that chronically alter the balance of calcium and to monitor the effectiveness of a treatment implemented for parathyroid disorders.

/ mL), considering the range between 1-7 pmol / L (or 10-70 pg / mL) as normal.

or a benign tumor of the parathyroid glands);

Hyperparathyroidism (often caused by kidney failure or taking specific drugs, including rifampicin, phosphates, anticonvulsants, steroids, isoniazid, etc.);

Vitamin D deficiency;

Pregnancy;

Menopause;

Lithium-based treatments.

;

High levels of phosphate;

Parathyroid removal surgery.

of an arm. In the laboratory, then, the dosage is performed, that is the measurement of the concentration of the protein in the blood sample taken.

Giulia Bertelli

Graduated in Medical-Pharmaceutical Biotechnology, she worked as a Research and Development Officer in Food Supplements and Dietary Food companies