Thyroid-Stimulating Hormone 

Updated: Jul 16, 2015
  • Author: Alina G Sofronescu, PhD; Chief Editor: Thomas M Wheeler, MD  more...
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Reference Range

Age-specific and pregnancy-specific reference intervals have been established. There are no significant sex or race specific differences.

Expected values using a third-generation immunochemiluminometric assay are as follows:

  • Premature, 28-36 weeks (first week of life): 0.7-27.0
  • Cord blood (>37 wk): 2.3-13.2
  • Children
    • Birth to 4 days: 1-39
    • 2-20 weeks: 1.7-9.1
    • 21 weeks to 20 years:0.7-64
  • Adults
    • 21-54 years: 0.4-4.2
    • 55-87 years: 0.5-8.9 
  • Pregnancy
    • First trimester: 0.3-4.5
    • Second trimester: 0.5-4.6
    • Third trimester: 0.8-5.2

The concentration of TSH in circulation is expressed as milli-international units of biological activity per liter of serum (mIU/L). This way of expressing the concentration originates from the way in which the TSH (and other hormones) was initially evaluated. TSH was initially measured using bioassay on colloidal tissue isolated from the guinea pig thyroid gland and an international unit was defined as the minimum amount of TSH that would elicit a biological response (stimulation of thyroid cAMP cyclase activity in these preparations). Currently all TSH assays are using WHO purified calibrators (second IRP 80/558), which have 7-5 pg purified human pituitary extract and are the equivalent of 37 mIU. (It should be noted that the pituitary extracts also contain small amounts of luteinizing hormone (LH) and follicle-stimulating hormone (FSH): 5-5% LH and 2-77% FSH. [1]

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Interpretation

Conditions associated with increases in TSH include the following:

Typical Laboratory Results in the Progression of Hashimoto Thyroiditis from Subclinical to Overt Disease (Open Table in a new window)

Stage of Disease TSH fT4 T3
Subclinical Increased Normal concentrations Normal concentrations
Early Increased Decreased Normal concentrations
Mature Increased Decreased Decreased

Conditions associated with decreases in TSH include the following:

  • Pituitary (secondary) hypothyroidism (rare)
  • Nonthyroid illness

Typical Laboratory Results in the Progression of Graves Disease from Subclinical to Overt Disease (Open Table in a new window)

Stage of Disease TSH fT4 T3
Subclinical Decreased Normal concentrations Normal concentrations
Early Decreased Normal concentrations Increased
Mature Decreased Increased Increased

Hypothyroidism

Signs or symptoms of hypothyroidism include the following:

  • Weight gain
  • Decreased appetite
  • Dry skin
  • Constipation
  • Cold intolerance
  • Puffy skin
  • Hair loss
  • Fatigue, lethargy
  • Menstrual irregularity
  • Blurred vision

Hyperthyroidism

Signs or symptoms of hyperthyroidism include the following:

  • Nervousness
  • Anxiety
  • Increased perspiration
  • Heat intolerance
  • Weight loss despite increase appetite
  • Hyperactivity
  • Tremor
  • Palpitations
  • Oligomenorrhea
  • Tachycardia or atrial arrhythmia
  • Systolic hypertension
  • Warm, moist, smooth skin
  • Lid lag
  • Stare
  • Muscle weakness

Other considerations

Drugs that can increase TSH include the following:

  • Dopamine antagonists
  • Chlorpromazine
  • Haloperidol
  • Iodine-containing drugs
  • Amiodarone (amiodarone-induced hypothyroidism) 

Drugs that can decrease TSH include the following:

  • Exogenous thyroxine,
  • Glucocorticoids
  • Dopamine
  • Levodopa
  • Dopamine agonists
  • Apomorphine
  • Pyridoxine
  • Amiodarone (early amiordarone therapy; amiodarone-induced thyrotoxicosis)
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Collection and Panels

Preferred specimen and acceptable tubes:

  • Serum (red top tube, SST)
  • Plasma (green top tube - sodium heparin, ammonium heparin, lithium heparin; PST)
  • Whole blood - newborn screening, collected by heel puncture 48-72 hours after birth
  • Specimen volume: 0.5 mL plasma or serum (0.25 mL minimum volume)

Specimen stability:

  • Centrifuge specimens and remove serum or plasma from the cells within 2 hours of collection.
  • Store at room temperature for 8 hours, or refrigerate at 2-8 degrees Celsius (36-46 degrees Fahrenheit) up to 5 days.
  • If assays are not completed within 48 hours, or the separated sample is to be stored beyond 48 hours, samples should be frozen at -20 degrees Celsius or colder. Frozen samples should be thawed only once. Analyte deterioration may occur in samples that are repeatedly frozen or thawed.

Related tests:

  • Thyroxine (T4)
  • Triiodothyronine (T3)
  • Antithyroid autoantibodies
  • Thyroxine binding proteins
  • Thyroglobulin (Tg)
  • Thyrotropin-releasing hormone (TRH)

Measurement of TSH

There are two major ways in which TSH is currently evaluated: Radioimmunoassay (RIA) and chemiluminescence immunoassays.

In the RIA, endogenous TSH present in the sample is competing with radiolabeled TSH for a limited amount of TSH-specific antibodies (“competitive assay”). The measured signal is inversely proportional with the amount of TSH present in the sample. [2]

The chemiluminescence assay is using two antibodies (“sandwich immunoassay”). The “capture antibody” is binding usually within the alpha subunit of TSH, while the “detection antibody” is always binding within the TSH-specific beta-subunit. The measured signal is directly proportional with the amount of TSH present in the sample. The chemiluminescence assay is significantly more sensitive than RIA; the current generation of immunometric assay (the fourth generation) has a functional detection limit of 0.001-0.002 mIU/L. [2]

As with all immunoassays, these assays are prone to specific interferences, especially heterophilic antibodies. Hook effect is rarely seen. Macro TSH can also be considered in the face of spurious results that do not match the clinical conditions and if other interferences are eliminated as well.

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Background

Description

Thyroid-stimulating hormone (TSH) is produced by the adenohypophysis. It promotes development of the thyroid gland and maintenance of its normal function. TSH stimulates the thyroid to produce and release the thyroid hormones: T4 and T3 (hypothalamus-pituitary-thyroid axis). Measurement of TSH frequently is included with that of T4 and T3 in a laboratory panel to screen for and to evaluate thyroid disease. The diagnosis of thyroid disorders can be complex, requiring the combined results of thyroid testing. [3, 4, 5, 6, 7, 2]

Indications/Applications

Indications for TSH testing include the following:

  • Screening for congenital hypothyroidism in newborns [2, 1]
  • Screening for subclinical hypothyroidism [8]
  • Diagnosis and monitoring of other thyroid disorders
  • Monitoring of patients receiving thyroid hormone
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