What are the laboratory tests for thyroid function?

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From the Guidelines

The primary lab tests for thyroid function include Thyroid-Stimulating Hormone (TSH) and Free Thyroxine (FT4) assays. Initial evaluation typically involves a TSH measurement, with abnormal results prompting further testing with FT4 and potentially Free Triiodothyronine (FT3) levels 1. In cases of suspected thyroid dysfunction, a Thyroid Panel may be ordered, which typically includes TSH, FT4, and FT3 measurements, to guide diagnosis and treatment with medications such as levothyroxine (50-200 mcg daily) or methimazole (5-30 mg daily) 1.

Key Laboratory Tests

  • TSH: primary screening test for thyroid dysfunction
  • FT4: used to differentiate between subclinical and overt thyroid dysfunction
  • FT3: may be used in cases of suspected hyperthyroidism or to monitor treatment efficacy

Diagnostic Approach

  1. Initial TSH measurement
  2. Abnormal TSH results prompt further testing with FT4 and potentially FT3
  3. Thyroid Panel may be ordered in cases of suspected thyroid dysfunction

Treatment Considerations

  • Levothyroxine (50-200 mcg daily) for hypothyroidism
  • Methimazole (5-30 mg daily) for hyperthyroidism
  • Treatment decisions based on TSH levels, clinical presentation, and other factors 1

From the Research

Laboratory Tests for Thyroid Function

The following laboratory tests are used to assess thyroid function:

  • Thyroid-stimulating hormone (TSH) test, which is the most commonly used test to evaluate thyroid function 2, 3, 4, 5, 6
  • Free thyroxine (FT4) test, which measures the level of thyroxine in the blood 2, 3, 4, 5, 6
  • Free triiodothyronine (FT3) test, which measures the level of triiodothyronine in the blood 3, 4, 6
  • Thyroglobulin (Tg) test, which measures the level of thyroglobulin in the blood 3, 4
  • Thyroid peroxidase antibodies (TPO-Ab) test, which measures the level of antibodies against thyroid peroxidase 4, 5
  • TSH receptor antibodies (TRAb) test, which measures the level of antibodies against the TSH receptor 4
  • Calcitonin test, which measures the level of calcitonin in the blood 3, 4
  • Antithyroglobulin antibodies (ATA) test, which measures the level of antibodies against thyroglobulin 3
  • Antimicrosomal antibodies (AMA) test, which measures the level of antibodies against the microsomal fraction of thyroid cells 3

Specialized Tests

In addition to the above tests, the following specialized tests may be used to evaluate thyroid function:

  • Fine needle aspiration cytology (FNAC), which is an invasive test used to collect tissue samples from the thyroid gland for histological examination 3
  • Ultrasonography, which is a non-invasive test used to evaluate the structure of the thyroid gland 3
  • Magnetic resonance imaging (MRI), which is a non-invasive test used to evaluate the structure of the thyroid gland 3
  • Positron emission tomography (PET), which is a non-invasive test used to evaluate the metabolic activity of the thyroid gland 3
  • Thyroidal radioiodine uptake test, which measures the uptake of radioactive iodine by the thyroid gland 3
  • Iodide uptake test, which measures the uptake of iodide by the thyroid gland 3

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Research

[Thyroid dysfunction in primary care medicine].

Revue medicale suisse, 2010

3
Research

Thyroid function tests: a review.

European review for medical and pharmacological sciences, 2009

6
Research

Methods for the investigation of thyroid function.

Methods in molecular biology (Clifton, N.J.), 2013

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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