Skip to main content

Medicare Coverage of Routine Screening for Thyroid Dysfunction (2003) / Chapter Skim
Currently Skimming:

2. Pathophysiology and Diagnosis of Thyroid Disease
Pages 14-20

The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.


From page 14...
... Dietary ingestion of iodide in the United States ranges between 200 and 500 ,ug/day and varies geographically; ingestion is higher in the western part of the United States than in the eastern states. The specialized thyroid epithelial cells of the thyroid gland are equipped with a Na/I symporter that helps concentrate iodide 30 to 40 times the level in plasma to ensure adequate amounts for the synthesis of thyroid hormone.
Read the entire page →
From page 15...
... On a weight basis, T3 is about 3 to 5 times more potent as a thyroid hormone than T4 and is believed to be the biologically active form of the hormone. TSH, secreted by thyrotroph cells located in the anterior pituitary gland, regulates thyroid gland function and hormone synthesis and release.
Read the entire page →
From page 16...
... TSH binds to a specific membrane receptor located on the surface of the thyroid epithelial cell and activates the cell signaling mechanisms through the enzyme adenylate cyclase located in the plasma membrane. Activation of adenylate cyclase increases intracellular cyclic adenosine monophosphate (cAMP)
Read the entire page →
From page 17...
... The most common cause of discordance between the TSH and free T4 result occurs in patients with subclinical thyroid dysfunction with high or low serum TSH values and a normal serum free T4 result. Serum TSH measurements may yield misleading results for individuals with changing levels of thyroid hormones.
Read the entire page →
From page 18...
... Thyroid Function Testing in the Elderly The prevalence of both low and high serum TSH levels (with normal serum free T4 results) is increased in elderly subjects compared with younger people.
Read the entire page →
From page 19...
... Effect of Medications on Thyroid Test Results Several medications have in vivo or in vitro effects on thyroid function tests that can create misleading results. Medications, notably estrogens, that raise serum TBG levels result in an increase in serum total T4 but no change in serum free T4 levels and no change in serum TSH concentrations.
Read the entire page →
From page 20...
... The effects of illness include decreased peripheral conversion of T4 to T3, decreases in serum concentrations of thyroid hormone binding proteins, and decreases in TSH secretion. These changes are reversible and do not seem to cause clinical manifestations of thyroid deficiency.
Read the entire page →

Key Terms

  • thyroid hormone
  • serum free
  • thyroid gland
  • thyroid function
  • low serum

  • thyroid hormones
  • thyroid dysfunction
  • tsh levels
  • tsh concentration
  • normal serum

  • thyroid test
  • hormone binding
  • serum concentrations
  • tsh values
  • primary hypothyroidism

  • function tests
  • tsh value
  • binding proteins
  • thyroid disease
  • tsh secretion

  • secondary hypothyroidism
  • serum total
  • adenylate cyclase
  • tsh concentrations
  • reference intervals

  • patients treated
  • thyroid epithelial
  • raise serum
  • nonthyroidal illness
  • misleading results


    • This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
    More information on Chapter Skim is available.