Does TSH Reliably Detect Hypothyroid Patients?

Area of Science:

• Endocrinology
• Clinical Chemistry

Background:

• Thyroid Stimulating Hormone (TSH) is a common screening test for thyroid dysfunction.
• Assessing thyroid function solely by TSH may lead to misdiagnosis in certain clinical scenarios.

Purpose of the Study:

• To evaluate the diagnostic reliability of normal TSH levels for thyroid function.
• To investigate the impact of Adrenocorticotropic Hormone (ACTH) on serum TSH concentrations.

Main Methods:

• Patients with hypothyroidism symptoms and normal TSH were assessed using mass spectrometry and immunoassay for thyroid hormones.
• The effect of ACTH stimulation on TSH levels was evaluated in patients undergoing adrenal function tests.

Main Results:

• Biochemical hypothyroidism was confirmed in patients with symptomatic hypothyroidism despite normal TSH and free T4 (FT4) by immunoassay, when assessed by mass spectrometry.
• ACTH stimulation led to a 17% average decrease in TSH levels within 60 minutes.
• Two cases illustrate successful thyroid hormone replacement in patients with discordant TSH and clinical presentation.

Conclusions:

• Normal TSH is not always a reliable indicator of thyroid function due to various influencing factors.
• Thyroid function assessment should incorporate multiple tests, especially when clinical presentation conflicts with TSH results.
• Mass spectrometry measurement of thyroid hormones is recommended for discordant cases.