Endocrine Abstracts

Background: TSH is the first-line test for thyroid function. Since the 1990s, 3^rd-generation assays have been available on automated platforms, and the normal ranges provided by manufacturers are generally used in diagnoses. In the age of gender medicine there is a need to refine normal TSH ranges. The aim of this study was to construct a normal TSH range in women living in our district.

Methods: From 2005 to 2020, 4544 records from women undergoing their first endocrinological examination were anonymously evaluated; 18% of records were excluded owing to lack of data (65%), age (<18 years; 18%), pregnancy (7%), non-Caucasian ethnicity (6%) and other reasons (4%). Age, BMI, TSH, TPOAb, pharmacological treatments and US findings were collected from 3724 records. 1638 were excluded owing to the presence of overt diseases, interfering treatments and TPOAb positivity. Thus, statistical analysis was performed on a sample of 2086 medical records. Data are reported as medians and 2.5-97.5 percentiles.

Results: Median TSH was 1.70 mIU/l (0.20-7.41 mIU/l). The median of TSH values collected from 2005 to 2020 ranged between 1.20 mIU/l (2005) and 1.99 mIU/l (2017), with significant differences between 2017 and 2005 (P<0.01), 2010 (P=0.03) and 2014 (P=0.02). On stratifying the sample into 3 age-groups (18-44 years, N=910; 45-64 years N=780; >65 years, N=393), TSH was 1.75 mIU/l (0.41-6.21 mIU/l), 1.66 mIU/l (0.20-6.93 mIU/l) and 1.52 mIU/l (0.07-7.78 mIU/l), respectively. In the whole sample, no correlation emerged between TSH levels and age or BMI. A significant (P<0.0001) decrease in the percentage of women considered to have sub-clinical hypothyroidism was observed when the upper limit of normal TSH was set at the age-related value of 97.5% (3.5%) instead of the TSH range reported in the assays (7.8%). By contrast, no difference in the percentage of women considered to have sub-clinical hyperthyroidism was noted when either the calculated age-related normal lower TSH limit (2.7%) or the manufacturers’ normal lower TSH range (2.3%) was applied.

Conclusions: This is the first study in Liguria aimed at establishing new age- and gender-specific reference values for TSH. Based on a large number of women (about 2% of adult women living in the Savona district), this new age-related range could be more extensively employed in order to improve diagnoses and therapies. The main result of implementing age- and gender-related normal TSH levels between the 2.5 and 97.5 percentiles seems to be a reduction in the hasty diagnosis of sub-clinical hypothyroidism.