Biological variation of thyroid function biomarkers over 24 hours

Area of Science:

• Clinical Chemistry
• Endocrinology
• Human Physiology

Background:

• Thyroid-stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), free T3 (FT3), and free T4 (FT4) are vital for diagnosing thyroid disorders.
• Accurate clinical decisions rely on robust biological variation (BV) data for these thyroid function biomarkers.

Purpose of the Study:

• To determine the short-term biological variation (BV) of key thyroid function biomarkers.
• To investigate sex-specific differences in the biological variation of these hormones.

Main Methods:

• Blood samples were collected from 31 healthy individuals at six time points over 24 hours.
• Thyroid biomarkers (TSH, T3, T4, FT3, FT4) were analyzed, and sex-stratified BV (CV_I, CV_G) was determined using nested ANOVA after data normalization.

Main Results:

• Significant sex-based differences were observed in the concentrations of all five thyroid biomarkers.
• Within-subject (CV_I) and between-subject (CV_G) variation estimates varied across hormones, with TSH showing higher CV_I (34.54%) compared to others.
• Individual index (II) values for T3, T4, FT3, and FT4 were ≤0.63, and males exhibited lower CV_I and II values than females.

Conclusions:

• Updated short-term BV data for thyroid function biomarkers reveal sex-specific variations, with most hormones showing lower CV_I than previously reported.
• The study provides essential, sex-stratified BV data, enhancing the reliability of thyroid function tests for clinical decision-making.