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New York Metro Local Section January 2010

January 2010 Answer

  A) Primary hyperthyroidism

Explanation

  • A very low TSH is almost always caused by either primary hyperthyroidism (suppression via high free thyroid hormone) or secondary hypothyroidism (decreased pituitary function).
  • In rare cases, it can be induced by medications. In this patient, high levels of T3and free T4are causing the low TSH, indicating primary hyperthyroidism.
  • In secondary hyperthyroidism, the TSH is elevated in addition to at least the T3.
  • Patients with an increased thyroxine-binding protein level have an increase in T3but not free T4or TSH and also have an increased unsaturated thyroxine-binding globulin (UTBG).
  • Patients with euthyroidsick syndrome usually have a low T3or T4, but a normal or slightly elevated TSH.

Reference

Harr, R.R. (2007). Clinical Laboratory Science Review, 3rded. [F.A. Davis Company pg 271]