Reference intervals for serum thyrotropin: dependence on the population investigated

Area of Science:

• Clinical Biochemistry
• Endocrinology
• Thyroidology

Background:

• Reference intervals for serum basal thyrotropin (TSH) are essential for diagnosing thyroid disorders.
• Existing TSH reference ranges may not be universally applicable across diverse patient demographics.

Purpose of the Study:

• To investigate potential differences in serum basal TSH reference intervals among various populations.
• To compare TSH responses in different patient groups and assess the predictive value of basal TSH.

Main Methods:

• Serum basal TSH levels were measured in euthyroid healthy volunteers, thyroid outpatients, geriatric patients, and seriously ill patients.
• Basal TSH results were compared with TSH responses (delta TSH) from the Thyrotropin Releasing Hormone (TRH) test.

Main Results:

• Normal ranges for basal TSH in euthyroid groups of different ages were similar.
• Significant positive correlations between basal and delta TSH were observed in all groups, but regression equations differed.
• The basal TSH cutoff for predicting a positive TRH-test was higher in geriatric groups ( > 0.7 mU/l) compared to others ( > 0.4 mU/l).
• Predictive values of basal TSH for indicating euthyroidism varied among populations, with higher thresholds needed for seriously ill patients.

Conclusions:

• Serum basal TSH reference intervals differ significantly across various populations.
• The sensitive TSH assay requires careful consideration of population-specific reference intervals when used for thyroid dysfunction screening.