Factors and Medications that Affect Thyroid and Antibody Blood Tests

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Pre-testing considerations for thyroid testing include identifying medications that affect thyroid and antibody blood tests. Insights into the pituitary-thyroid-hypothalamus relationship also indicate a need to identify medications that affect the thyroid upstream and downstream to the pituitary and hypothalamus. Measurements are designed to test the thyroid gland’s production of T4 and T3, as well as TSH from the pituitary gland and the hypothalamus’s TSH Releasing Hormone. The thyroid gland located in the bottom of the front of your neck is a critical gateway for energy production metabolism and controls other hormones' production. Testing thyroid function is common because as many as 50% of the population will encounter thyroid problems.

Thyroid Assessment is Complicated

Thyroid assessment involves not just taking serum (blood) hormone production tests because they are not adequate for the complexities of thyroid action. Hormonal supply should be assessed by thyroid tissue reaction. These metabolic indices from thyroid tissue are also not adequate, as these responses are altered by a variety of mechanisms, both physiologic and pathologic. If T4, T3 and TSH hormones are irregular, a disease state is likely. However, since the thyroid functions with the pituitary and hypothalamus, other factors must be considered. Endocrine specialists can evaluate the whole picture but certain factors and medications must be considered in the evaluation process.

Factors Affecting Your Thyroid

Your specialist may test over 100 factors influencing the thyroid system including:

  • Iodine concentration
  • Temperature
  • Basal Metabolic Rate
  • Deep Tendon Reflex Relaxation Time (Photomotogram)
  • Tests Related to Cardiovascular Function

Those factors may or may not be affected by the medications that you take. The endocrine specialist will examine your history, symptoms and medications to properly evaluate you.

Medications Affecting the Thyroid Test

Common preparations, over the counter drugs, and minerals may affect your thyroid test and your thyroid health. Common medications that affect thyroid and antibody blood tests are:

  • lithium: thyroid antibodies have been found with intake of lithium. Lithium is concentrated in the gland and interferes with thyroid hormone synthesis/release and an increase in thyrotropin levels.
  • estrogen and estrogen-containing birth control pills: interferes with total T4 and total T3 measurements.
  • heroin and methadone hydrochloride: interferes with total T4 and total T3 measurements.
  • dopamine agonists: suppress thyrotropin levels to lower-than-normal values. Thyrotropin is undetectable in patients with true hyperthyroidism.
  • nonsteroidal anti-inflammatory drugs: displace thyroid hormones from thyroid-binding globulin, increase FT4 and FT3 concentrations and depress thyrotropin levels.
  • androgens: interferes with total T4 and total T3 measurements.
  • iodides: are hidden in many preprations and non-prescription drugs; can induce iodide hypothyroidism and goiter.
  • anabolic steroids: interferes with total T4 and total T3 measurements.
  • nicotinic acid: interferes with total T4 and total T3 measurements.
  • glucocorticoids: interferes with total T4 and total T3 measurements.
  • beta blockers and corticosteroids: minimally inhibit the peripheral conversion of T4 to T3.



Thyroid Disease Manager, Thyroid Function Tests

West J Med. 2000 February; 172(2): 102–106, How Medications Affect Thyroid Tests