Thyroid Flashcards
What is elevated in most hyperthyroid patients and decreased in hypothyroidism?
*What is found in <5% of Hyperthyroid patients?
Total T4 (Thyroxine)
- <5% of Hyperthyroid patients:
- Normal T4 but elevated T3 (“T3 Toxicosis”)
Since T4 and T3 are highly bound, fluctuations in serum proteins somewhat limit their values, What are the two main binding proteins?
- Prealbumin (Transthyretin)
- Thyroid Binding Globulin (TBG)
Measurements of what, correlates well with clinical thyroid status?
Free T4 (FT4) and Free T3 (FT3)
What is Reverse T3 (rT3)?
*It is elevated in what?
rT3 is a metabolic product of T4 (most of which is metabollized to T3)
*rT3 is elevated in Euthryoid Sick Syndrome
Thyroid Function Test Patterns - Hyperthyroidism:
- TSH
- T3
- T4 (Total)
- T4 (Free)
- rT3
Hyperthyroidism:
- TSH - Low
- T3 - High
- T4 (Total) - High
- T4 (Free) - High
- rT3 - wnl
Thyroid Function Test Patterns - Hypothyroidism:
- TSH
- T3
- T4 (Total)
- T4 (Free)
- rT3
Hypothyroidism:
- TSH - High
- T3 - Low
- T4 (Total) - Low
- T4 (Free) - Low
- rT3 - wnl/Low
Thyroid Function Test Patterns - Euthyroid Sick Syndrome:
- TSH
- T3
- T4 (Total)
- T4 (Free)
- rT3
Euthyroid Sick Syndrome:
- TSH - wnl
- T3 - Low
- T4 (Total) - wnl/Low
- T4 (Free) - wnl/Low
- rT3 - High
Thyroid Function Test Patterns - Excess TBG:
- TSH
- T3
- T4 (Total)
- T4 (Free)
- rT3
Thyroid Function Test Patterns - Excess TBG:
- TSH - wnl
- T3 - High
- T4 (Total) - High
- T4 (Free) - wnl
- rT3 - wnl
What is the clinical scenario for testing Thyroid Releasing Hormone (TRH)?
Evaluation of Hypothyroidism
An exaggerated secretion of Thyroid Stimulating Hormone (TSH) in response to Thyroid Releasing Hormone (TRH), suggests what?
Primary Hypothyroidism
-Hypothyroidism d/t Intrinsic Thyroid Hypofunction
An inappropriate TSH response to TRH stimulation suggests what?
Hypopituitarism
What is the best first line test for diagnosing hypo- and hyperthyroidism?
Thyroid Stimulating Hormone
TSH; Thyrotropin
TSH levels:
- Hypothyroidism
- Hyperthyroidism
TSH levels:
- Hypothyroidism - High
- Hyperthyroidism - Low
In which clinical scenarios may TSH not be the best screening test? (3)
- Hypothalamic dysfunction
- Pituitary dysfunction
- Neonatal Screening (fT4)
What is the next step if FT4 is normal despite a low TSH?
Measure free T3 (FT3)
-Assess for T3 throtoxicosis
What is the most common cause of Hyperthyroidism?
Graves disease
Graves Disease is characterized by the presence of what? (1+)
-Which other antibodies may also be seen? (2)
Thyroid Stimulating Immunoglobulin (TSI)/Long Acting Thyroid Stimulating (LATS) Antibodies
- Antimicrosomal Abs (60%)
- Antithyroglobulin Abs (30%
What is the most common cause of Hypothyroidism?
Hashimoto Thyroiditis
Hashimoto Thyroiditis is characterized by the presence of what 2 antibodies?
- Antitissue Peroxidase Abs (>90%)
- Antithyroglobulin Abs (>90%)
What is Neonatal Hypothyroidism most often caused by?
Thyroid Dysgenesis
Neonatal Hypothyroidism:
- Complications (if untreated)
- MC Test for evaluation
- Mental/Growth Retardation
- TSH assay alone
What is the effect of Exogenous Estrogens on Thyroid function?
Increases TBG
- Increase Total Thyroxine (T3/T4)
- Free Thyroxine and TSH are WNL
What medication inhibits the release of Thyroxine from the Thyroid gland, resulting in Hypothyroidism?
Lithium
Amiodarone effect on Thyroid Function:
- Developed countries (iodine rich)
- Underdeveloped countries (iodine poor)
Amiodarone effect on Thyroid Function:
- Developed countries (iodine rich) - Hypothyroidism
- Underdeveloped countries (iodine poor) - Hyperthyroidism
