CEACAM5 and medullary thyroid gland carcinoma: Laboratory values determined on the basis of the suspicion of MTC showed highly elevated levels of calcitonin (537.3 pmol/L, normal range ≤ 1.72 pmol/L) and carcinoembryonic antigen (CEA) (31.1 ng/mL, normal range ≤ 2.5 ng/mL), without the use of proton-pump inhibitors, along with euthyroidism.