Calcitonin: current concepts and differential diagnosis.

Area of Science:

• Endocrinology
• Oncology
• Biochemistry

Background:

• Calcitonin (CT) is a hormone produced by thyroid parafollicular cells, acting via the calcitonin receptor (CTR).
• Elevated CT levels (hypercalcitoninemia) can stem from various causes, including tumors, hypercalcemia, renal issues, or drug reactions.
• Basal calcitonin (bCT) is an indicator, but not definitive, for medullary thyroid carcinoma (MTC).

Purpose of the Study:

• To review current understanding of CT biosynthesis and physiology.
• To provide updated information on the differential diagnosis of elevated CT levels.
• To discuss the clinical utility of CT measurements in MTC diagnosis and management.

Main Methods:

• Literature review of CT biosynthesis, physiology, and clinical applications.
• Analysis of diagnostic criteria and interpretation of basal and stimulated calcitonin (bCT and sCT) tests.
• Discussion of extrathyroidal CT production and its implications.

Main Results:

• Age- and gender-specific cutoff values for bCT are recommended for MTC screening.
• bCT >100 pg/ml has high positive prognostic value for MTC; levels between 8-100 pg/ml (males) and 6-80 pg/ml (females) warrant further testing.
• Stimulation tests (e.g., with calcium or pentagastrin) are debated due to sensitive immunoassays; sCT <2 times bCT may rule out MTC.

Conclusions:

• Elevated bCT levels, particularly above 100 pg/ml, are strongly associated with MTC.
• Careful interpretation of bCT and sCT, considering age and gender, is essential for MTC diagnosis.
• Extrathyroidal tumors can also produce CT, necessitating a broad differential diagnosis for hypercalcitoninemia.