Serum calcitonin may be elevated in

Calcitonin is a polypeptide of 32 amino acids derived from ultimobranchial body. It is secreted from C cells of thyroid (parafollicular cells). It lowers the plasma calcium and phosphorus levels. It blocks the PTH induced bone resorption. Calcium from the circulation is shunted into the bone. It increases the excretion of calcium, phosphorus, sodium and potassium. Normally it is less than 0.08 ng/L (undetectable). It is increased in medullary carcinoma of thyroid. It is very good tumour marker for MCT. It confirms the relapse/ metastases/residual disease. Increased levels in family members confirm the genetic relation and such relatives should undergo prophylactic total thyroidectomy. Reference : page 488 SRB's manual of surgery 5th edition