Endocrine Abstracts

Background: Hypothyroidism is defined as an elevated TSH (thyroid-stimulating hormone) and/or decreased free thyroxine (FT4) levels. Levothyroxine is now one of the most widely prescribed medications. However, treatment indications are controversial in subclinical hypothyroidism, defined as high TSH with normal T4 levels.

Methods: We performed a cross-sectional study reviewing the blood samples received in our Laboratory for TSH determination during the period of 10th Jun 2019–21st Oct 2019. We did not search for access to medical background or any private information regarding the patients whose samples were analysed. Any TSH above the upper limit of normal for our laboratory (4.94 mU/l for adult patients, CMIA, Abbott Architect) and up to 20 mU/l was included to the study group. Among samples with TSH above 20 mU/l, we only included those with normal FT4 or T4 level determined from the same sample. The selected samples were treated with Polyethylene glycol (PEG) in the same manner as for high prolactin levels. We calculated the TSH recovery level (monomeric TSH) as a percentage of the initial TSH level.

For statistical analysis, we used IBM SPSS v.21 and MaxStat v.3.6. We applied non-parametric tests and defined P < 0.05 as significant.

Results: Of 12 703 samples, 430 (3.4%) met the inclusion criteria. Of these, 398 had available serum for precipitation with PEG. Patients with initial TSH < 15 mU/l were younger than those with TSH 15 mU/l or above (P = 0.03). The group with recovered TSH percentage of up to 24% (n = 106) had a lower initial TSH value when compared with 25% or higher (n = 292) (P = 0.01). Older age (50 and older, n = 200) was associated with a higher level of monomeric TSH (P = 0.003). The initial TSH values of 7.77 mU/l or above had tendency towards higher value of monomeric TSH (P = 0.066).

Conclusions: Our results suggest there could be a potential role for monomeric TSH determination prior to treatment initiation for subclinical hypothyroidism, mainly in young patients. The main strong point of our study is its real-world setting. The limitations are that we did not take into account the patients’ background and treatment; we also did not have a possibility to use gel filtration chromatography which is considered a gold standard for monomeric TSH determination. At the next stage, we are planning to compare these results with a group of patients who have normal TSH values.