Endocrine Abstracts

Objectives: Different scientific societies recommend performing screening for clinical primary hypothyroidism during the first trimester of pregnancy using local normality ranges of TSH and just in the lack of these, should the American population reference levels be used. Our objective is to determinate the reference range of TSH during the 1^st trimester of pregnancy in our healthcare area and the impact of its implantation.

Material and methods: Prospective study where women selected had no history of thyroid pathology nor where taking any drugs that may disrupt thyroid function. TSH, FT4 and anti-thyroid antibodies (TPOab, TGab, TRab) were determined between week 9 and 11. TSH >5 μU/ml, positive thyroid autoimmunity or any condition that may interfere were excluded (final n=282). Reference levels were defined by calculating the confidence interval between p2.5 and p97.5 of the distribution. Tests for hypothyroidism screening in the last two years were reviewed and variations on the diagnosis of hypothyroidism depending on the TSH reference level used was analysed.

Results: New local reference level for the 1^st trimester: TSH 0.17–4.39 μU/ml; T4L 0.97–1.88 ng/dl. Screening tests in the last 2 years (1/12/2014 to 30/11/2016) n=6032. Diagnosis of hypothyroidism using American standard reference levels (TSH> 2.5 μU/ml): 35.8% (2181 women). Diagnosis of hypothyroidism with our reference levels (TSH >4.39 μU/ml): 8,6% (524 women). Total number of TSH ≥ 10 μU/ml: 0.6% (37 women).

Conclusions: Reference levels for TSH in our study are similar to others in different Spanish areas and differ significantly from the American reference range, those standard ranges imply an unacceptable rate of diagnosis of hypothyroidism (one out of three women), even more if a universal screening strategy is carried out. Determination and implementation of locally assessed reference levels would avoid overdiagnosis, unnecessary treatment and follow-up.