Thyroid-Stimulating Hormone

Normal thyroid-stimulating hormone (TSH) findings are as follows (although values differ between laboratories) ^[1] :

• Adult: 2-10 μU/mL
• Newborn: 3-18 μU/mL
• Cord: 3-12 μU/mL

Conditions associated with increases in TSH include the following:

• Congenital hypothyroidism

• Primary hypothyroidism

• TSH-secreting pituitary tumors (uncommon)

• Pituitary resistance to thyroid hormone (uncommon)

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

Conditions associated with decreases in TSH include the following:

• Hyperthyroidism

• 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)

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)

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.

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, 8]}

• Screening for subclinical hypothyroidism ^[9]

• Diagnosis and monitoring of other thyroid disorders

• Monitoring of patients receiving thyroid hormone