Thyroid function tests
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** |
|
| Radiation-induced | |||||||||||
| Trauma induced | |||||||||||
| Radioiodine induced | |||||||||||
| Thyroidectomy | |||||||||||
| Subclinical hypothyroidism | - | - | ↑ | Normal | Normal | Normal | Normal | Normal | Normal/↑ |
| |
(†)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
- Thyroid function tests may differentiate various causes of hyperthyroidism:[2][3][4][5][6][7][8][9][10]
| 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 |
|
| Toxic thyroid nodule | - | - | ↓ | ↑ | Normal/↑ | ↑(hot nodule) | Normal/↑ | Normal | Absent | Absent |
- | |
| Secondary hyperthyroidism | Pituitary adenoma | - | - | ↑ | ↑ | Normal/↑ | ↑ | Normal/↑ | Normal | Absent | Absent |
|
| Tertiary hyperthyroidism | Tertiary hyperthyroidism | - | - | ↑ | ↑ | ↑ | ↑ | Normal/↑ | ↑ | Absent | Absent |
|
| Drug induced | Amiodarone type 1 | - | - | ↓ | ↑ | Normal/↑ | ↓ | Normal/↑ | Normal | Absent | Absent |
|
| Amiodarone type 2 | - | - | ↓ | ↑ | Normal/↑ | Absent/↓ | Normal/↑ | Normal | Absent | Absent |
| |
| Others | Factitious thyrotoxicosis | - | - | ↓ | ↑ | Normal/↑ | ↓ | ↓ | Normal | Absent | Absent |
|
| Trophoblastic disease | - | - | ↓ | ↑ | Normal/↑ | ↑ | - | Normal | Absent | Absent |
- | |
| Struma ovarii | - | - | ↓ | ↑ | Normal/↑ | ↓ | - | Normal | Absent | Absent |
- | |
(†)T3RU; Triiodothyronine Resin uptake. (^)TPOAb; Thyroid peroxidase antibodies.
References
- ↑ "Utilização dos testes de função tireoidiana na prática clínica".
- ↑ 2.0 2.1 Bindra A, Braunstein GD (2006). "Thyroiditis". Am Fam Physician. 73 (10): 1769–76. PMID 16734054.
- ↑ 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.
- ↑ 4.0 4.1 "Thyroiditis — NEJM".
- ↑ 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.
- ↑ 6.0 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.
- ↑ 7.0 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.
- ↑ "Clinical Finding and Thyroid Function in Women with Struma Ovarii".
- ↑ Vaidya B, Pearce SH (2014). "Diagnosis and management of thyrotoxicosis". BMJ. 349: g5128. PMID 25146390.
- ↑ "Think thyrotoxicosis factitia - measure thyroglobulin | The BMJ".