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

Area of Science:

• Endocrinology
• Clinical Chemistry
• Public Health

Background:

• Thyroid hormone reference ranges are crucial for diagnosing thyroid dysfunction.
• Existing reference intervals may not accurately reflect diverse populations like Indian adults.
• Establishing population-specific norms is essential for accurate clinical interpretation.

Purpose of the Study:

• To generate thyroid hormone reference norms for apparently healthy Indian adults.
• To establish reference intervals for free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) using electro-chemiluminescence.
• To provide sex-specific and age-specific reference values.

Main Methods:

• A cross-sectional study was conducted on 1916 apparently healthy Delhi adults (aged 18-86 years).
• Subjects with pre-existing thyroid conditions or risk factors were excluded using strict criteria.
• Thyroid hormone levels (FT3, FT4, TSH) and urinary iodine excretion were measured.

Main Results:

• The reference population had a mean age of 41.2 ± 18.1 years and a median urinary iodine excretion of 233.6 μg/L.
• Overall FT3 ranged from 2.4-8.8 pmol/L, FT4 from 10.1-24.8 pmol/L, and TSH from 2.2 ± 0.9 mIU/L.
• FT3 levels were significantly higher in men than in women (p=0.001).

Conclusions:

• Centiles for FT3, FT4, and TSH were derived for Indian adults.
• This study established mean reference intervals for FT3, FT4, and TSH across different age groups and sexes.
• The derived reference norms are suitable for use in the Indian adult population.