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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Furqan M M. M.B.B.S[2]

Synonyms and Keywords: TFTs

Overview

Thyroid function tests (TFTs) is a collective term for blood tests used to check the function of the thyroid. A TFT panel typically includes thyroid-stimulating hormone (TSH, thyrotropin) and thyroxine (T4), and triiodothyronine (T3) depending on local laboratory policy.TFTs may be requested if a patient is thought to suffer from hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid) or to monitor the effectiveness of either thyroid-suppression or hormone replacement therapy. It is also requested routinely in conditions linked to thyroid disease, such as atrial fibrillation. The normal adult reference range for serum TSH is 0.4-4.5 mIU/L. The adult reference range of FT4 using comparative direct methods is 0.7-1.8 ng/dL (9-23 pmol/L) and that for FT3 is 2.3-5.0 pg/mL (35-77 pmol/L). A high TSH level may indicate hypothyroidism. If the results indicate high TSH levels, a second confirmatory sample including TSH and free T4 levels should be tested prior to starting treatment. TSH should not be measured in isolation in patients with suspected hypothalamic-pituitary disease; the measurement of free T4 is essential. Free T4 testing, combined with TSH testing, is recommended for the routine assessment and diagnosis of thyroid function and following hyperthyroidism treatment and may or may not be used in cases of hypothyroidism.

Thyroid function tests

Thyroid function tests serve as an important diagnostic tool in the diagnosis and follow-up of various hyper and hypothyroid states:[1]

  • The normal adult reference range for serum TSH is 0.4-4.5 mIU/L. A high TSH level may indicate hypothyroidism. If the results indicate high TSH levels, a second confirmatory sample including TSH and free T4 levels should be tested prior to starting treatment.
  • The adult reference range of FT4 using comparative direct methods is 0.7-1.8 ng/dL (9-23 pmol/L) and that for FT3 is 2.3-5.0 pg/mL (35-77 pmol/L).
  • TSH should not be measured in isolation in patients with suspected hypothalamic-pituitary disease; the measurement of free T4 is essential. Free T4 testing, combined with TSH testing, is recommended for the routine assessment and diagnosis of thyroid function and following hyperthyroidism treatment and may or may not be used in cases of hypothyroidism.
  • Serum T3 testing has a low sensitivity and specificity for diagnosing hypothyroidism.
  • Abnormal levels of total T4 and T3 often result from changes in transport proteins, not thyroid function. Total hormone testing should only be performed when there are discrepancies in the free hormone levels.
  • Conditions other than thyroid disease should be considered when TSH levels are abnormal such as physiological changes associated with pregnancy, severe nonthyroidal illness, and medication use (including amiodarone, lithium, dopamine, and glucocorticoids).

Differential Diagnosis

Increased TSH levels

Decreased TSH levels

Thyroid function tests in hypothyroidism

Disease History and symptoms Laboratory findings Additional findings
Fever Pain TSH Free T4 T3 T3RU Thyroglobin TRH TPOAb^
Primary hypothyroidism Autoimmune (Hashimoto's thyroiditis) - - * Normal/ Normal/↓ Normal/ Normal Present (high titer)
Riedel's thyroiditis - - Normal/↑ Normal/↓ Normal/↓ Normal/↓ Normal Normal Usually present
Infectious thyroiditis + + Normal Normal Normal Normal Normal Normal Absent
Transient hypothyroidism Subacute (de Quervain's) thyroiditis +/- +/- ↑/ ↓/ Normal Normal Low/absent
Postpartum thyroiditis +/- +/- ↑/ ↓/ Normal Normal/↑ Present (high titer)
Silent thyroiditis - - ↑/ ↓/ Normal Normal Present (high titer)
Others Drug-induced - - /↓ /↑ Normal Normal/ Normal Absent**
  • History of hyperthyroidism
  • History of trauma
  • History of drug use, surgery, or radiation
Radiation-induced
Trauma induced
Radioiodine induced
Thyroidectomy
Subclinical hypothyroidism - - Normal Normal Normal Normal Normal Normal/
  • Asymptomatic


(†)T3RU; Triiodothyronine Resin uptake. (^)TPOAb; Thyroid peroxidase antibodies. (*)TSH may be decreased transiently in the thyrotoxicosis. (**)TPOAb may be present in drug-induced hypo/hyperthyroidism such as Interferon-alpha, interleukin-2, and lithium.

Thyroid function tests in hyperthyroidism

Disease History and symptoms Laboratory findings Additional findings
Fever Pain TSH Free T4 T3 T3RU Thyroglobin TRH TSH Receptor Antibody TPOAb^
Thyroiditis Hashimoto's thyroiditis (Hashitoxicosis) - - * Normal/ Normal/↓ Normal/ Normal Absent Present (high titer)
Subacute (de Quervain's) thyroiditis +/- +/- ↑/ ↓/ Normal Normal Absent Low/absent
Postpartum thyroiditis +/- +/- ↑/ ↓/ Normal Normal/↑ Absent Present (high titer)
Silent thyroiditis - - ↑/ ↓/ Normal Normal Absent Present (high titer)
Primary hyperthyroidism Grave's disease - - Normal/ Normal Present Absent
  • Patient may have opthalmopathy and dermopathy
Toxic thyroid nodule - - Normal/↑ ↑(hot nodule) Normal/ Normal Absent Absent

-

Secondary hyperthyroidism Pituitary adenoma - - Normal/↑ Normal/ Normal Absent Absent
  • Inappropriately normal or increased TSH
Tertiary hyperthyroidism Tertiary hyperthyroidism - - Normal/ Absent Absent
  • Inappropriately normal or increased TSH
Drug induced Amiodarone type 1 - - Normal/↑ Normal/ Normal Absent Absent
  • High urinary iodine
Amiodarone type 2 - - Normal/↑ Absent/↓ Normal/ Normal Absent Absent
  • High urinary iodine
Others Factitious thyrotoxicosis - - Normal/↑ Normal Absent Absent
  • Decreased thyroglobulin
Trophoblastic disease - - Normal/↑ - Normal Absent Absent

-

Struma ovarii - - Normal/↑ - Normal Absent Absent

-

(†)T3RU; Triiodothyronine Resin uptake. (^)TPOAb; Thyroid peroxidase antibodies.

References

  1. "Utilização dos testes de função tireoidiana na prática clínica".
  2. 2.0 2.1 Bindra A, Braunstein GD (2006). "Thyroiditis". Am Fam Physician. 73 (10): 1769–76. PMID 16734054.
  3. 3.0 3.1 McDermott MT (2009). "In the clinic. Hypothyroidism". Ann. Intern. Med. 151 (11): ITC61. doi:10.7326/0003-4819-151-11-200912010-01006. PMID 19949140.
  4. 4.0 4.1 "Thyroiditis — NEJM".
  5. 5.0 5.1 Aoki Y, Belin RM, Clickner R, Jeffries R, Phillips L, Mahaffey KR (2007). "Serum TSH and total T4 in the United States population and their association with participant characteristics: National Health and Nutrition Examination Survey (NHANES 1999-2002)". Thyroid. 17 (12): 1211–23. doi:10.1089/thy.2006.0235. PMID 18177256.
  6. 6.0 6.1 Lania A, Persani L, Beck-Peccoz P (2008). "Central hypothyroidism". Pituitary. 11 (2): 181–6. doi:10.1007/s11102-008-0122-6. PMID 18415684.
  7. 7.0 7.1 De Groot LJ, Chrousos G, Dungan K, Feingold KR, Grossman A, Hershman JM, Koch C, Korbonits M, McLachlan R, New M, Purnell J, Rebar R, Singer F, Vinik A, Stockigt J. "Clinical Strategies in the Testing of Thyroid Function". PMID 25905413.
  8. "Clinical Finding and Thyroid Function in Women with Struma Ovarii".
  9. Vaidya B, Pearce SH (2014). "Diagnosis and management of thyrotoxicosis". BMJ. 349: g5128. PMID 25146390.
  10. "Think thyrotoxicosis factitia - measure thyroglobulin | The BMJ".

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