Thyroid Stimulating Hormone

Aka: Thyroid Stimulating Hormone, TSH, Serum TSH, Thyrotropin

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II. Physiology

  1. See Thyroid Physiology
  2. Thyroid Stimulating Hormone (TSH) is a Glycoprotein synthesized in the Basophil cells of the anterior pituitary
  3. Regulation
    1. Positive Stimulation
      1. Thyroid Releasing Hormone (TRH, Thyrotopin Releasing Hormone, from Hypothalamus)
    2. Negative feedback
      1. Unbound Thyroxine (Free T4)
      2. Unbound Triiodothyronine (Free T3)
  4. Thyroid Stimulating Hormone (TSH) promotes all aspects of Thyroid Hormone production
    1. Increases Iodide uptake
    2. Incorporation of Iodine into Thyroglobulin
    3. Thyroglobulin lysis into active Thyroid Hormones T4 and T3
    4. Stimulates proliferation of increased Thyroglobulin synthesizing cells (Cuboidal cells) in Thyroid follicles
  5. Variation
    1. TSH levels follow a circadian rhythm
      1. TSH will vary as much as 1-2 uIU/ml over the course of the day
      2. Consider drawing TSH at the same time of day for longterm serial measurements
    2. TSH levels increase with normal aging in euthyroid patients
      1. Consider using age-adjusted TSH interpretation
      2. Age 20-29: 3.56 mIU/ml is 97th percentile
      3. Age >80: 7.49 mIU/ml is 97th percentile
      4. Surks (2007) JCEM 92: 4575 [PubMed]
    3. Pregnancy
      1. See Thyroid Dysfunction in Pregnancy
      2. See Hypothyroidism in Pregnancy
      3. Maintaining euthyroid state in pregnancy is critical
    4. Euthyroid individuals still have considerable variation in TSH levels over time
    5. Populations of euthyroid individuals also have considerable variation in TSH levels

III. Interpretation: Non-Pregnant

  1. Normal
    1. Random: 0.3 - 5.0 uIU/ml
    2. Following Thyroid Releasing Hormone (TRH) stimulation
      1. TSH: 9-30 uIU/ml at 20-30 min
  2. Borderline Increased: 5-10 uIU/ml
  3. High: >10 uIU/ml

IV. Interpretation: Pregnancy

  1. Non-pregnanct: 0.3 to 4.3 mIU/ml
  2. First trimester: 0.1 to 2.5 mIU/ml
  3. Second trimester: 0.2 to 3.0 mIU/ml
  4. Third timester: 0.3 to 3.0 mIU/ml
  5. Abbassi (2010) Obstet Gynecol 114(6): 1326-31 [PubMed]

V. Causes: Increased TSH

  1. Hypothyroidism
  2. Drugs
    1. Amiodarone
    2. Lithium
    3. Haloperidol
    4. Chlorpromazine
    5. Metoclopramide
    6. Metyrapone
    7. Domperidone
  3. TSH antibodies
  4. Pituitary resistance
  5. Thyrotropin Releasing Hormone (TRH) Secreting Tumor
  6. Acute illness (esp. elderly)
    1. Wong (1981) Arch Intern Med 141(7):873-5 +PMID: 7235805 [PubMed]

VI. Causes: Decreased TSH

  1. Hyperthyroidism
  2. Euthyroid Sick Syndrome (associated with acute illness)
  3. Central Hypothyroidism
    1. Hypopituitarism or Pituitary Ademoma causing TSH deficiency and low T4 and T3
  4. Hyponatremia
  5. Malnutrition
  6. Mood Disorders
  7. Medications
    1. Amiodarone
    2. Interferon
    3. Interleukin-2
    4. Opiates
    5. Corticosteroids
    6. Levothyroxine
    7. Levodopa
    8. Dopamine Agonists
    9. Pyridoxine
    10. Bromocriptine
    11. Somatostatin analogs
    12. Carbemazepine
    13. Metformin
    14. Biotin (High dose, >5000 mcg/day)

VII. References

  1. Haugen (2009) Best Pract Res Clin Endocrinol Metab 23(6): 793–800 [PubMed]

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