Endocrine Abstracts

Macro TSH is a large molecular-sized thyroid-stimulating hormone (TSH) that is including TSH and anti-TSH antibody. Patients with macro TSH have elevated serum TSH and normal free thyroxine levels similar to subclinical hypothyroidism. A 18-year old female patient was referred from gynecology and obstetrics to endocrinology clinic for evaluating of elevated TSH with normal free thyroxine levels. Laboratory and clinical investigations revealed that only discordant TSH levels (normal reference range: 0.25–4.2 μIU/ml; two times separately checked results; 5.65 μIU/ml; 5.47 μIU/ml; respectively) with electrochemiluminescence immunoassay method with no other any demonstrable hormonal or clinical findings. On admission to our endocrinology department, she was clinically euthyroid. She had no history of medication or ilness. The patient had normal thyroid ultrasound pattern with tested mildly positive for both thyroglobulin and thyroid peroxidase antibodies. Rheumatoid factor, which can act like heterophile antibodies, was undetectable in this patient. Polyethylene glycol (PEG) method for TSH measurement was planned to find out the macro-TSH. We have used the same blood samples which of the TSH levels were found to be high, while using the PEG method was found to be within normal ranges as 1.50 mIU/L (5.65 μIU/ml to 1.50 μIU/ml; decrease of 75%) and 1.26 mIU/l (5.47–1.26 μIU/ml, decrease of 77%); respectively. The TSH value was exhibited to be markedly low by PEG precipitation test in our patient that she had PEG-precipitable TSH ratios greater than 75% as well as it’s supposed to be reported by Hattori et al study. Macro-TSH should be kept in mind in patients with high TSH levels without symptoms of hypothyroidism in the differential diagnosis before unnecessary investigations and treatment.