EP14 – Detection of macro-TSH (mTSH) in a cohort of patients with a history of thyroid cancer: A case-controlled study

      Giusti, Massimo1; Conte, Lucia1; Repetto, Anna Maria2;  Gay, Stefano1;  Marroni, Paola2; Mittica, Miranda1; Mussap, Michele2 1 UO Clinica Endocrinologica, Azienda Ospedaliera Universitaria San Martino – IST, Genoa, Italy 2 UO Laboratorio Analisi, Azienda Ospedaliera Universitaria San Martino – IST, Genoa, Italy   Background/ Purpose: Macro-TSH can accumulate in circulation, elevating TSH levels. Aim of this study was to evaluate the prevalence of mTSH in patients who had undergone thyroidectomy for cancer. Methods: To date, 39 patients and 14 controls with benignant pathology have been evaluated. Thyroidectomy was performed in all subjects. In all but 2 cases Tg/calcitonin levels were indicative of cure. All subjects were on L-T4. Free-T4 and TSH were evaluated by ECLIA (Roche). MTSH was screened by adding PEG to serum. Results: The percentage recovery of TSH (RTSH%) after PEG-precipitation was regarded as an inverse expression of mTSH. RTSH% of <20% was considered suggestive of mTSH. RTSH% was 32.8±8.5% in thyroid cancer patients and 35.7±11.8% in controls. RTSH% <20% was found only in 2 cases (5%). In all patients, no correlation was found between RTSH% and age, sex, BMI, years since thyroidectomy, tumor stage, radioiodine therapy, Tg levels, TgAb state, body weight-related L-T4 posology, concomitant drugs or f-T4 and TSH levels. Limitations: data collection is still ongoing. Though arbitrary, the choice of a 20% cut-off for RTSH% is in line with literature data. Conclusion: Free TSH levels after PEG precipitation are very low in all subjects. The presence of mTSH seems to be a rare phenomenon in thyroid cancer. Body weight seems to be the predominant determinant in L-T4 posology to maintain an adequate TSH. The evaluation of more serum samples could add further data in patients, in whom a balance is required between adequate TSH suppression and the avoidance of unnecessary hyperthyroxinemia


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