Detection of Polyethylene Glycol Thyrotropin (TSH) Precipitable Percentage (Macro-TSH) in Patients with a History of Thyroid Cancer

• Published in: Endocrinology and metabolism (Seoul) Vol. 32; no. 4; pp. 460 - 465
• Main Authors: Massimo Giusti, Lucia Conte, Anna Maria Repetto, Stefano Gay, Paola Marroni, Miranda Mittica, Michele Mussap
• Format: Journal Article
• Language: Korean
• Published: 대한내분비학회 31.12.2017
• Subjects: Levothyroxine-posology; Macro-thyrotropin; Polyethylene glycol-precipitable thyrotropin; Thyroid neo-plasms; Thyrotropin
• ISSN: 2093-596X

Background: Owing to its large molecular size, polyethylene glycol (PEG)-precipitable thyrotropin (TSH) can accumulate in the circulation, elevating TSH levels. PEG-precipitable TSH can be used to detect macro-TSH (mTSH) in serum. Our aim was to evaluate the prevalence of mTSH in patients who had undergone thyroidectomy for thyroid cancer. Methods: Seventy-three thyroid cancer patients and 24 control subjects on levothyroxine (LT4) TSH-suppressive or replacement therapy were evaluated. Screening for mTSH was performed by adding PEG to serum in order to precipitate γ-globulin. A percentage of PEG-precipitable TSH ≥80% was considered suggestive of mTSH. Results: No correlation between free-T4 (fT4) and TSH levels was found. PEG-precipitable TSH was 39.3%±1.9% in thyroid cancer patients and 44.1%±3.9% in controls. Macro-TSH was deemed to be present in one thyroid cancer patient and in two control subjects. Only in the thyroid cancer group was PEG-precipitable TSH found to be negatively correlated with fT4 concentration. No correlation was found between PEG-precipitable TSH and other clinical conditions in any patients. Conclusion: The presence of mTSH seems to be a rare phenomenon in thyroid cancer. In some patients with low PEG-precipitable TSH, a reduction in LT4 dosage could be suggested. LT4 dosage adjusted to body weight is the main factor in maintaining TSH in a semi-suppressed or normal range. Evaluation of mTSH could be necessary in patients in whom a balance is required between adequate TSH suppression and the avoidance of unnecessary exogenous hyperthyroxinemia.