What is parathormone?
Parathormone is a hormone consisting of 84 amino acids (protein building blocks) and is also called PTH or parathyrin. If the calcium level in the blood drops (hypocalcemia), the so-called main cells of the parathyroid glands produce parathormone. This reaches the bones primarily via the blood. Here it stimulates the osteoclasts via a complex system. These are special cells that break down bone tissue. Calcium and phosphate are released in the process.
At the same time, parathormone influences the kidneys and ensures that more phosphate is excreted through the urine and calcium is reabsorbed into the body.
Overall, this means that parathormone increases the calcium level and lowers the phosphate level in the blood. The less phosphate there is in the blood, the more calcium can be freely present in the blood, otherwise the two combine to form a poorly soluble complex. The calcium-phosphate complexes can be deposited in tissues, organs and also arteries and lead to circulatory disorders.
Vitamin D3 (calcitriol) is also synthesized in the kidney by parathyroid hormone. In the intestine, it increases calcium absorption from the diet.
The counterpart of parathormone is the hormone calcitonin, which is produced in the thyroid gland. It has the opposite effect to parathyroid hormone: calcitonin lowers the calcium level and increases the phosphate level.
The doctor measures the parathyroid hormone level in the blood if he suspects a disturbance of the calcium-phosphate balance. In addition, the measured value provides indications of diseases of the parathyroid gland, such as hyper- or hypofunction. The parathormone value (PTH value) is always determined together with the calcium and phosphate values.
Parathormone normal values
The parathormone level in the blood is determined from the serum. Blood is usually taken in the morning from an empty patient. Various enzymes break down the parathormone quickly, which is why the sample must be processed quickly. In healthy adults, the parathyroid hormone level in the blood is normally between 15 and 65 picograms per milliliter (pg/ml). Note: As with many laboratory values, the exact reference range is method dependent.
When is parathyroid hormone too low?
As a normal reaction of the body, parathyroid hormone is always low when the calcium level in the blood is high (hypercalcemia). However, the calcium level can also be elevated due to disease, as a result of which the parathyroid hormone remains too low.
If parathyroid hormone and calcium are reduced at the same time, there is an underactive parathyroid gland (hypoparathyroidism): Although the calcium content is too low, the parathyroid glands are not able to produce and secrete more parathormone as a counter-reaction. In the most frequent cases, the cause is surgery on or in the area of the thyroid gland or autoimmune processes. In the worst case, hypocalcemia leads to seizures and cardiac arrhythmias.
When is parathyroid hormone too high?
As mentioned above, parathyroid hormone physiologically increases when calcium is low in the blood (hypocalcemia). In some people, however, there is an overactivity of the parathyroid glands in which too much parathormone is produced. This is called hyperparathyroidism.
In most cases, this is an autonomic hyperfunction (primary hyperthyroidism). In the majority of cases, it is caused by a benign tumor (adenoma) of the parathyroid gland. Another possible cause is an enlargement (hyperplasia) or – more rarely – a malignant tumor (carcinoma) of the parathyroid gland.
Any form of hyperparathyroidism triggers increased bone loss and remodeling. This can be seen on X-rays and often causes bone and joint pain. Other possible symptoms include nausea, vomiting, kidney stones and gastrointestinal ulcers.
What to do if parathyroid hormone is elevated or decreased?
Treatment is based on the underlying disease. The decreased calcium levels in hypoparathyroidism can be compensated by orally ingested calcium and vitamin D. The treatment of tumors belongs in the hands of experienced oncologists.
In primary hyperparathyroidism, the independently (autonomously) functioning parts of the parathyroid glands are surgically removed. Therapy for secondary hyperparathyroidism in the setting of kidney disease includes balanced fluid intake and strict blood pressure control. In addition, phosphate-rich foods such as nuts should be avoided and vitamin D should also be taken. The goal is to normalize the parathyroid hormone level in the blood.
