Falsely Elevated Thyroid Stimulating Hormone in Two Cases Requiring Special Follow-up

"Inappropriate thyroid stimulating hormone (TSH)" refers to an elevation in TSH levels that does not match the clinical findings and free T3 and free T4 levels. Several conditions can cause this, such as pituitary tumors that produce TSH, resistance to thyroid hormones, macro-TSH, and antibody interference. Macro-TSH is a condition that causes TSH to be measured high in the blood for a long time by forming a complex with immunoglobulins, mostly IgG. However, patients are clinically euthyroid because macro-TSH is not a bioactive complex. It is essential to exclude the diagnosis of falsely elevated TSH to protect patients from unnecessary or high -dose levothyroxine therapy. In our first case, we presented a patient in whom subclinical hypothyroidism was detected during in vitro fertilization treatment, and levothyroxine was started. The other case was an operated papillary thyroid cancer patient. In both cases, although the dose of levothyroxine was increased, insufficient TSH response to increased fT4/fT3 levels suggested inappropriate TSH elevation. The polyethylene glycol (PEG) precipitation method was used to detect the assay variability. TSH recovery after PEG was 0.96016 and 21016, respectively, supporting the diagnosis of macro-TSH. In both cases, detecting Macro-TSH was crucial in preventing thyrotoxicosis caused by excessive levothyroxine dosage. In addition, delay in treatment for infertility was prevented in the first case.