Indirect estimation of reference intervals for thyroid parameters

Area of Science:

• Clinical Chemistry
• Laboratory Medicine
• Endocrinology

Background:

• Establishing population-based reference intervals for laboratory tests is resource-intensive and time-consuming.
• Routine laboratory data offers a potential source for deriving indirect reference intervals.
• This study explores the feasibility of using patient results for indirect reference interval determination.

Purpose of the Study:

• To determine indirect reference intervals for thyroid hormones from routine patient laboratory results.
• To assess the accuracy and efficiency of indirect reference interval determination compared to traditional methods.

Main Methods:

• Retrospective analysis of thyrotropin (TSH), total thyroxine (T4), free thyroxine (fT4), triiodothyronine (T3), and free triiodothyronine (fT3) results (2008-2011).
• Logarithmic transformation of data to exclude outliers and estimation of non-parametric reference intervals.
• Statistical tests to compare subgroups and validate reference interval significance.

Main Results:

• No significant differences were found in most thyroid hormone levels across subgroups, allowing for combined reference values.
• A significant difference in TSH was observed between ambulatory and hospitalized patients in 2011.
• Indirect reference values were established for TSH (0.42-3.67 mIU/L), T4 (66.0-136.10 nmol/L), fT4 (10.20-18.40 pmol/L), T3 (1.10-2.39 nmol/L), and fT3 (3.17-5.59 pmol/L).

Conclusions:

• Indirect determination of laboratory-specific reference intervals is a practical and economical method.
• The precision of indirect reference limits is enhanced when data distribution exhibits minimal skewness and kurtosis.
• This approach provides a valuable alternative for establishing accurate reference ranges in clinical laboratories.