Serum thyrotropin and free thyroxine reference ranges as defined in a disease-free sample of French middle-aged adults

Abstract

Background: The goal of this study was to provide reference ranges for thyrotropin (TSH) and free thyroxine (fT₄) based on data collected from a disease-free sample of French middle-aged adults.

Methods: A total of 3218 subjects participating in the Supplémentation en Vitamines et Minéraux Antioxydants (SU.VI.MAX) study had measurements for TSH, fT₄ and urinary iodine concentrations. Thyroid volume and structure were evaluated using standardized ultrasonography. We selected a disease-free sample which included 2338 subjects (1313 females aged 35–60 years and 1025 males aged 45–60 years) with normal thyroid imaging, no previously reported thyroid disease or use of thyroid medication, and no risk factors for thyroid dysfunction. Distribution of TSH and fT₄ was estimated in males and females.

Results: The median (central 95% range) TSH serum concentrations for females were 1.79 mU/L (0.29–5.21 mU/L) for ages 35–44 years and 1.98 mU/L (0.27–6.94 mU/L) for ages 45–60 years (p<0.0001, for age). The median (central 95% range) for males 45–60-year-old was 1.63 mU/L (0.28–4.54 mU/L) (p<0.0001, for sex). Sex- and age-specific mean fT₄ concentrations did not differ significantly (p=0.06) between males and females and (p=0.08) between female age groups. However, median fT₄ concentrations between 45–60-year-old males and females differed (p<0.001).

Conclusions: In middle-aged adults, the TSH distribution was associated with gender and, among females, with age. Stratification according to gender and age should be considered when TSH ranges are used in the diagnosis, treatment and monitoring of thyroid disease.

Clin Chem Lab Med 2009;47:1497–505.