Synonym

• TSH
• Thyrotropin

Tubes

Red-top or Tiger tope tube.

5 mL of venous blood.

Filter paper may be used for neonate.

Info

Thyroid Stimulating Hormone (TSH) is a pituitary hormone which is produced in response to Thyrotropin Releasing Hormone (TRH) from the hypothalamus.

Clinical

This test is the best single test for thyroid function.

I. Screening for thyroid dysfunction

1. TSH decreased with hyperthyroidism
2. TSH increased with hypothyroidism

II. Monitoring thyroid replacement therapy (e.g. Levothyroxine)

III. Monitoring anti-thyroid therapy (e.g. propylthiouracil, methimazole or radioactive iodine)

One caution is the rare situation in which there is primary hypothalamic-pituitary dysfunction resulting in an inappropriate TSH. When this is suspected Free T4 and T3 should be measured. Clinical indicators should alert the clinician to suspect this.

For patients on thyroxin supplementation (e.g. such as thyroxine or Synthroid®) the TSH is an appropriate single test that can be followed and used to determine need for adjusting dosing. A high TSH is an indication to increase the thyroxine dose and a low TSH indicates a need to decrease the thyroxine dose. A TSH in the normal range is the goal for patients on supplementation.

Suppressive therapy such as propylthiouricil (PTU) or methimazole (Tapazole®) may also be monitored to look for a normalization of the TSH with successful therapy.

Hypothyroid state clinically manifests itself with some of the following:

• Flattened affect/facial expression
• Deepened voice
• Delayed deep tendon reflexes
• Mild hypothermia
• Bradycardia
• Loss of axillary, pubic, scalp hair
• Increased diastolic and decreased systolic blood pressure
• Pale-Waxy cool skin
• Thin, brittle hair and nails
• Enlarged tongue
• Slow clumsy movements
• Myxedema (non-pitting edema pretibial, hands, infraorbital)
• Weakness
• Fatigue/Low energy
• Periods irregular or heavy
• Weight gain
• Cold intolerance
• Myalgia/Arthralgia/Paresthesias
• Constipation
• Headaches
• Depression.
• In severe cases, coma and respiratory failure may occur.

Hyperthyroid state clinically manifests itself with some of the following:

• Fatigue
• Heat intolerance
• Palpitations
• Loose of frequent stools
• Weight loss
• Exercise intolerance
• Sweating
• Hair loss
• Anxiety
• Tremor
• Tachycardia
• Hyperreflexia
• Proximal muscular weakness
• Stare / Lid lag
• Atrial fibrillation
• Widened pulse pressure
• With Grave's disease, may see additional items of diplopia, blurry vision, bruit of thyroid gland, exophthalmos, periorbital or pretibial edemia, clubbing and gynecomastia.

Nl Result

Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.

Note: Neonates (birth to 3 days) have high TSH at birth and these usually normalize within 3-7 days to adult levels.

High Result

A high TSH occurs when the pituitary gland senses insufficient circulating thyroid hormone. In response to this the pituitary secretes TSH to stimulate thyroid gland production of thyroid hormone.

Conditions consistent with this value include:

• Ablative hypothyroidism
• Euthyroid sick syndrome
• Hashimoto's thyroiditis
• Infantile hypothyroidism
• Primary hypothyroidism
• TSH secreting tumor
• Thyroid hormone resistance
• During recovery from illness, in going from a catabolic to anabolic state, there may be a transient rise in the TSH.
• Drugs known to increase TSH include:
  • Amiodarone
  • Benserazide
  • Beta blockers (atenolol, propranolol)
  • Calcitonin
  • Erythrosine
  • Flunarizine (males)
  • Iobenzamic acid
  • Iodides/Radiographic agents
  • Lithium
  • Methimazole
  • Metoclopramide
  • Morphine
  • Phenytoin
  • Rifampin
  • Sumatriptan
  • Tamoxifen
  • TRH
  • Valproic acid

Low Result

A low TSH occurs when the pituitary gland senses too much circulating thyroid hormone. In response to this, the pituitary diminishes TSH production thus stopping the signal to the thyroid gland to produce thyroid hormone.

Conditions consistent with a low TSH include:

• Primary hyperthyroidism
• Grave's disease
• Exogenous thyroid hormone (in excess)
• Hypothalamic or pituitary failure
• Drugs known to decrease TSH include:
  • Acetylsalicylic acid (Aspirin)
  • Amiodarone
  • Carbamazepine
  • Danazol
  • Dopamine
  • Interferon alfa-2a
  • Nifedipine
  • Octreotide
  • Pyridoxine
  • Somatostatin
  • Steroids (Anabolic & Corticosteroids)
  • Thyroid hormone replacement agents

References

• Emerg Med Clin N Am 23 (2005) 649-667
• Filippi, L. Dopamine infusion: A possible cause of undiagnosed congenital hypothyroidism in preterm infants. Pediatr Crit Care Med 2006 May;7(3);249-251.
• Kabadi, UM, et al. Serum thyrotropin in primary hypothyroidism. A possible predictor of optimal daily levothyroxine dose in primary hypothyroidism. Arch Intern Med 1995; 155:1046-8;
• Ladenson, PW. American Thyroid Association Guidelines for Detection of Thyroid Dysfunction Arch Intern Med 2000;160:1573-5.
• Rosen's Emergency Medicine: Concepts and Clinical Practice, 5th ed.
• Toft, AD. Thyroxine therapy. N Engl J Med 1994;331:174-80
• Williams Textbook of Endocrinology, 10th ed.
• Conn's Current Therapy 2005, 57th ed.
• The Osler Medical Handbook, 1st ed.