April - June 2015, Volume 11, Issue 2

Yalcin MM, Ayvaz G, Gulbahar O, Toruner F, Ozkan C, Altinova AE, Akturk M, Arslan M

A Rare Cause of Discordant TSH: MACRO-TSH

Acta Endo (Buc) 2015, 11 (2): 170-173
doi: 10.4183/aeb.2015.170

When the laboratory results are not compatible with the clinical features of the patient, the presence of assay interference should be considered. Patient and Methods. Here, we report a case of macro-thyroid stimulating hormone (macro-TSH) in a 31 yearold woman who had hypothyroidism due to thyroidectomy as well as discordant TSH levels with the clinical findings. Her TSH level was spuriously high with low levels of free T3 and T4 on levothyroxine treatment and she had only mild fatigue. To screen for the presence of interference, we performed TSH measurements in different platforms and serial dilution of the sample. Her rheumatoid factor was found to be negative. Results. The testing for heterophile blocking and non-specific anti TSH antibodies suggested lack of interference. We did further test for the clinical suspicion of interference and TSH decreased to 29.8 μIU/mL from 210.5 μIU/mL (recovery: 14.1%) after polyethylene glycol (PEG) precipitation indicating the existence of macro-TSH. After two months of increased dosage of levothyroxine, her TSH level was still very high (192.0 μIU/mL), but free T3 and free T4 increased to normal levels. PEG precipitation test was reperformed and TSH was decreased to 46.0 μIU/mL from 192.0 μIU/mL (recovery: 24.0 %). Her levothyroxine replacement dosage was not increased since free T3 and T4 levels were normal. Conclusions. If there is a suspicion for the discordant TSH level, the presence of macro-TSH by PEG precipitation should be investigated even though first step investigations for interference were found to be negative.

Keywords: macro-TSH, interference, PEG.

Correspondence: Mehmet Muhittin Yalcin, Gazi University Faculty of Medicine, Endocrinology and Metabolism, Gazi Universitesi Endokrinoloji ve Metabolizma bölümü, Ankara, 06500, Turkey, E-mail: yalcin.muhittin@gmail.com