Detection of polyethylene glycol thyrotropin (TSH) precipitable percentage (macro-TSH) in patients with a history of thyroid cancer

Massimo Giusti, Lucia Conte, Anna Maria Repetto, Stefano Gay, Paola Marroni, Miranda Mittica, Michele Mussap

Research output: Contribution to journalArticlepeer-review


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 ?-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.

Original languageEnglish
Pages (from-to)460-465
Number of pages6
JournalEndocrinology and Metabolism
Issue number4
Publication statusPublished - Dec 1 2017


  • Levothyroxine-posology
  • Macro-thyrotropin
  • Polyethylene glycol-precipitable thyrotropin
  • Thyroid neoplasms
  • Thyrotropin

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Endocrinology


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