Definition of parathyroid hormone analysis in the blood
Parathyroid hormone, PTH, is a hormone secreted by the parathyroid glands. It plays a major role in regulating the distribution of calcium in the body. Its main role is to stimulate the release of calcium by the bones and the reabsorption of calcium in the kidneys to increase blood calcium levels.
Thus, the parathyroid hormone has a “hyper-calcemic” and “hypo-phosphoremic” effect (it lowers phosphate levels at the same time).
In the blood, we find the intact hormone (PTH 1-84) but also fragments that complicate the dosage.
Why do a parathyroid hormone analysis?
The dosage of parathyroid hormone is recommended in cases:
- hypercalcemia (too much calcium in the blood)
- abnormalities of the phosphocalcic balance
- kidney stones (renal lithiasis)
- for the follow-up of people with renal failure on dialysis
- to guide the diagnosis of vitamin D deficiency.
The dosage may also be recommended in postmenopausal women with osteoporosis.
It is always carried out at the same time as a “phosphocalcic” assessment, i.e. a measurement of calcium and blood phosphate levels.
What results can be expected from a parathyroid hormone analysis?
The dosage is done from a venous blood sample. No preparation is necessary. The doctor may ask you to stop taking certain medications before the test, which can affect the results.
Several types of measurements are used and results may vary from one analytical laboratory to another. In general, the concentration of PTH in the blood varies between 6 and 50 pg/ml (picograms per milliliter).
Its rate may be too high or too low. The doctor, by combining this dosage with the phosphocalcic balance, will be able to guide his diagnosis.
Thus, in case of too high a PTH level associated with hypercalcemia, it is likely that the diagnosis of hyperparathyroidism is made. There are many causes (including some cancers).
In the case of elevated PTH and hypocalcemia, it may be secondary hyperparathyroidism. The main causes are vitamin D deficiency and kidney failure.
On the contrary, in the case of decreased PTH, hypocalcemia, and hyperphosphatemia, it is probably hypoparathyroidism. This can be secondary to the removal of the thyroid, but also to pathologies such as hemochromatosis or inflammatory or infectious diseases.
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