thyroid function test
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Introduction
A collective term used for laboratory tests to check the function of the thyroid.
Pathology
- non-thyroid illness is commonly associated with changes in thyroid function test; no treatment necessary
- see specific thyroid disease
- higher serum TSH & lower serum free T4 within the reference interval are associated with longer life expectancy (up to 3.5 years)[5]
Physiology
- thyroid function is controlled by 2 main processes
- pituitary secretion of TSH
- peripheral conversion of T4 into T3
- T4 is a prohormone, T3 confers most of the physiological action of thyroid hormone
Indications
- assessment of hypothyroidism
- assessment of hyperthyroidism
- monitoring thyroid replacement therapy
Contraindications
- use in hospitalized patients in the absence of strong clinical suspicion of thyroid dysfunction[1]
Drug interactions
- inhibition of TSH synthesis or release
- decreased thyroid hormone synthesis or release
- decreased conversion of T4 to T3
- amiodarone (transient effect, < 3 months, in 85%)[1]
- corticosteroids
- ipodate, iopanoic acid
- propranolol (high dose)
- propylthiouracil
- decreased thyroxine-binding globulin*
- increased thyroxine-binding globulin*
- enhanced metabolic clearance of T4#
- displacement of T4 from binding proteins
- drugs inhibiting absorption or enterohepatic circulation$ of thyroxine (T4)
- drugs causing thyroiditis
- spurious laboratory results[1]
- amiodarone (high free T4, low serum T3, normal serum TSH)
- biotin > 5-10 mg/day (high free T4, low serum TSH)
- carbamazepine, oxcarbazepine, phenytoin
- enoxaparin, heparin (high free T4, low serum T3, normal serum TSH)
- salsalate (low free T4, low serum T3, normal serum TSH)
* affects total serum T4 & serum T3, but not free T4 or free T3[1]
# higher dose of thyroxine may be needed to normalize serum TSH in patients with hypothyroidism[1]
$ separate from thyroxine dosing by several hours[1]
Laboratory
- serum TSH sensitive initial test for thyroid disorders[1]
More general terms
More specific terms
- anti-thyroid peroxidase (microsomal) antibody
- free thyroxine index (fT4I)
- pentagastrin stimulation test (calcitonin-stimulation test)
- radioactive iodine uptake (RAIU) test
- T3 resin uptake
- T3 total in serum/plasma
- thyroglobulin antibody in serum
- thyroglobulin in serum
- thyroid-stimulating hormone (TSH) in serum; thyrotropin in serum
- thyroxine [T4] (free) in serum
- thyroxine [T4] (total) in serum
- TRH stimulation test
- triiodothyronine [T3] (free) in serum
Additional terms
References
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Medical Knowledge Self Assessment Program (MKSAP) 15, 16, 17, 18, 19. American College of Physicians, Philadelphia 2009, 2012, 2015, 2018, 2022.
- ↑ Wikipedia: Thyroid function tests http://en.wikipedia.org/wiki/Thyroid_function_test
- ↑ Tabatabaie V, Surks MI. The aging thyroid. Curr Opin Endocrinol Diabetes Obes. 2013 Review. PMID: https://www.ncbi.nlm.nih.gov/pubmed/23974775
- ↑ Demers LM, Spencer CA. Laboratory medicine practice guidelines: laboratory support for the diagnosis and monitoring of thyroid disease. Clin Endocrinol (Oxf). 2003 Feb;58(2):138-40. PMID: https://www.ncbi.nlm.nih.gov/pubmed/12580927
- ↑ 5.0 5.1 Bano A, Dhana K, Chaker L et al Association of Thyroid Function With Life Expectancy With and Without Cardiovascular Disease. The Rotterdam Study. JAMA Intern Med. Published online September 18, 2017 <PubMed> PMID: https://www.ncbi.nlm.nih.gov/pubmed/28975207 <Internet> http://jamanetwork.com/journals/jamainternalmedicine/article-abstract/2653451
- ↑ Burch HR Drug Effects on the Thyroid. N Engl J Med 2019; 381:749-761. Aug 22. PMID: https://www.ncbi.nlm.nih.gov/pubmed/31433922 https://www.nejm.org/doi/full/10.1056/NEJMra1901214