Reference intervals of serum thyroid function tests in a previously iodine-deficient area.

Area of Science:

• Endocrinology
• Thyroidology
• Public Health

Background:

• Iodine deficiency historically impacts thyroid function.
• Establishing accurate thyroid function test (TFT) reference ranges is crucial for diagnosis and management.
• Previous data may not reflect current thyroid function in populations with changing iodine status.

Purpose of the Study:

• To establish current reference data for serum thyroid function tests.
• To determine reference intervals for thyrotropin (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) in a specific region.
• To assess the need for region-specific reference ranges in formerly iodine-deficient areas.

Main Methods:

• Analysis of data from 4298 individuals aged 20-79 years.
• Measurement of serum TSH, FT3, FT4, and anti-TPOAb.
• Thyroid ultrasound to evaluate thyroid structure and size for reference population selection.

Main Results:

• A reference population of 1488 individuals was selected, excluding those with known or undiagnosed thyroid disorders.
• Established reference intervals: TSH 0.25-2.12 mIU/L, FT3 3.8-7.0 pmol/L, FT4 8.3-18.9 pmol/L.
• Reference TSH levels differed from US population values and manufacturer-provided ranges.

Conclusions:

• Thyroid function test reference ranges in this formerly iodine-deficient region are distinct from those in iodine-sufficient areas.
• Thyroid ultrasound is essential for creating a reference population to exclude undiagnosed thyroid disorders.
• Region-specific reference ranges are necessary for accurate thyroid function assessment.