Young adult reference ranges for thyroid function tests on the Centaur immunoassay analyser

This study aims to establish reference ranges for thyroid tests in young Saudi adults using the Centaur immunoassay method. Physical examination is performed and thyroid function tests include thyroid stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyronine (FT3). These are performed on 291 young Saudi adults (182 [63%] females and 109 [37%] males; average age: 27 years [range 18-50]). Clinical thyroid abnormality, related symptoms and/or abnormal thyroid function tests exclude a person from the study and thus a total of 276 subjects (171 [62%] females and 105 [38%] males) are used to establish the new reference ranges. Combined female and male ranges for TSH, FT4, and FT3 were found to be 0.48-6.30 miu/L (9.00-18.62 pmol/L and 3.39-6.85 pmol/L, respectively). Mean TSH and FT4 levels were significantly different (P<0.0001) from those quoted by the manufacturer. Ranges for TSH were 0.48-6.30 miu/L (female) and 0.52-4.89 miu/L (male) (P=0.08). Female ranges for FT4 and FT3 were 9.00-17.15 pmol/L and 3.39-5.82 pmol/L, respectively. Male ranges were 9.92-18.62 pmol/L (P=0.0001) and 4.36-6.85 pmol/L (P<0.0001). The range of TSH levels in the young local Saudi population proved to be higher than that quoted by the manufacturer. FT4 range was lower and narrower than that quoted by the manufacturer. Significant differences between female and male populations suggest that partitioning of the reference ranges by gender is necessary.