The main limitation in systematic calcitonin determination lies in the difficulties in establishing reliable cut-off values, because calcitonin concentration physiologically increases with age and weight, differs according to sex, and may result in false positive cases due to its secretion in neuroendocrine disorders, in lung/pancreas cancer, nephropathy, hypergastrinemia, thyroid autoimmunity. The gene discussed is CALCA; the disease is autoimmune thyroid disease.