Reference range of thyroid function (FT3, FT4 and TSH) among Indian adults

To generate thyroid hormone reference norms using electro-chemiluminescence technique.

Cross sectional study on apparently normal 4349 Delhi adults (18-86 years). Predetermined exclusion criteria (goiter, hypoechogenicity or nodularity on ultrasound, elevated anti-thyroid peroxidase antibody, hypo or hyperthyroidism and family history of thyroid dysfunction) excluded 2433 subjects leaving 1916 (916 males and 1000 females) as the reference population.

Mean age and BMI of the reference population were 41.2 ± 18.1 years and 24.5 ± 4.4 kg/m(2) respectively. Median urinary iodine excretion was 233.6 μg/L (79-458;3rd-97th centile). The population was categorized into various age groups (18-30, 31-40, 41-50, 51-60, 61-70 and ≥ 70 years). Overall FT3 and FT4 values in the reference population irrespective of age, ranged from 2.4-8.8 (mean 4.6 ± 0.9) pmol/L and 10.1-24.8 (mean 15.40 ± 2.0) pmol/L, respectively. Mean TSH value in the reference population was 2.2 ± 0.9 mIU/L which was significantly lower than that of total population (3.8 ± 6.1; p<0.001).

FT3 values were observed to be significantly higher in men than women (p=0.001). The centiles (3rd, 5th, 10th, 25th, 50th, 75th, 90th, 95th and 97th) of FT3, FT4 and TSH were derived for reference purposes in Indian adults. This community based study in Indian adults has established mean reference intervals for FT3, FT4 and TSH for different age groups for both sexes separately using strict exclusion criteria. These can be used as reference norms for Indian adults.