Reference intervals for thyroid disorders calculated by indirect method and comparison with reference change values

Area of Science:

• Clinical Biochemistry
• Endocrinology
• Laboratory Medicine

Background:

• Accurate reference intervals (RIs) are crucial for interpreting thyroid function tests.
• Manufacturer-provided RIs may not always reflect population-specific variations.
• Evaluating RIs using reference change values (RCVs) can assess their clinical significance.

Purpose of the Study:

• To establish population-based RIs for thyroid stimulating hormone (TSH), free thyroxine (fT4), and free triiodothyronine (fT3).
• To assess the clinical utility of these RIs by comparing them with manufacturer-provided intervals using RCVs.

Main Methods:

• Analysis of a large laboratory dataset (188,912 patients) for TSH, fT4, fT3, Anti-TPO, and Anti-Tg.
• Measurements performed using electrochemiluminescence immunoassay on Cobas c801.
• Comparison of estimated RIs with manufacturer RIs utilizing RCVs.

Main Results:

• TSH RIs did not differ significantly by gender or age (0.41-4.37 mIU/mL).
• fT4 and fT3 RIs showed significant differences based on gender and age subgroups.
• Estimated RIs for TSH and fT4 were within RCVs of manufacturer RIs, while fT3 showed a greater difference.

Conclusions:

• Indirect estimation of RIs from laboratory data can be more accurate than manufacturer values.
• Population-based RIs, validated with RCVs, offer valuable insights for clinical interpretation.
• Gender and age-specific RIs for fT4 and fT3 are recommended for improved diagnostic accuracy.