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Calcitonin assay is used in identifying patients with nodular thyroid diseases. It is helpful in making an early diagnosis of medullary carcinoma of thyroid. A malignancy of the parafollicular cells, i.e. medullary thyroid cancer (MTC), typically produces an elevated serum calcitonin level. Prognosis of MTC depends on early detection and treatment.
Parafollicular cells secrete calcitonin, a hormone that participates in the regulation of calcium metabolism. Calcitonin lowers blood levels of calcium by inhibiting the resorption of bone by osteoclasts , and its secretion is increased proportionally with the concentration of calcium.
For most substances presented, the optimal levels are the ones normally found in the population as well. More specifically, optimal levels are generally close to a central tendency of the values found in the population. However, usual and optimal levels may differ substantially, most notably among vitamins and blood lipids, so these tables give ...
The level of procalcitonin in the blood stream of healthy individuals is below the limit of detection (0.01 μg/L) of clinical assays. [3] The level of procalcitonin rises in a response to a pro-inflammatory stimulus, especially of bacterial origin. It is therefore often classed as an acute phase reactant. [4]
Elevated calcitonin levels in the blood have been shown to be associated with the rare medullary thyroid cancer. However, the measurement of calcitonin levels as a diagnostic tool is currently controversial due to falsely high or low calcitonin levels in a variety of diseases other than medullary thyroid cancer. [26] [27]
The effects of calcitonin are opposite those of the parathyroid hormone (PTH) produced in the parathyroid glands. However, calcitonin seems far less essential than PTH, since calcium metabolism remains clinically normal after removal of the thyroid (thyroidectomy), but not the parathyroid glands. [43]
At the same time, the parathyroid glands reduce the secretion of parathyroid hormone (PTH), also a polypeptide hormone, into the blood. The resulting high levels of calcitonin in the blood stimulate osteoblasts in bone to remove calcium from blood plasma and deposit it as bone. The reduced levels of PTH inhibit removal of calcium from the skeleton.
In these patients, injecting pentagastrin will cause calcitonin levels to rise significantly above the normal or basal range. [4] After a total thyroidectomy for medullary thyroid carcinoma, the pentagastrin-stimulated calcitonin release can be used to detect residual parafollicular C-cells.