Endocrine Thyroid Flashcards
What is the HPT axis?
TRH –> TSH –> T4 (and some T3)
Where is T4 converted to T3?
Peripheral tissues
If TSH is high, you expect what for T4 in normal patient?
High T4
If T4 is low and TSH is high, what is going on?
Thyroid gland problem, there is NO negative feedback (abnormal!)
How would septic patient look with regards to thyroid hormones?
Subclinical hypothyroidism
High TSH, T4 normal
for subclinical hyperthyroidism (rare)
Low TSH, T4 normal
If T4 is not converted to T3, what is it?
Reverse T3 (not normal!)
Indicates patient has problem or is septic
Hypothyroid TSH is ___, T4 is ___
high, T4 low
Hyperthyroid TSH is ___, T4 is ___
low, T4 high
Most common cause of hypothyroid? Most common cause of hyperthyroid?
Hashimotos (hypo)
Graves disease (enlarged thyroid gland)
What is newborn hypothyroidism?
Cretinism
For Thyroid storm, do you block alpha or beta first?
Alpha, unopposed alpha can lead to stroke or arrhythmia
Which thyroid nodule is higher cancer risk?
Cold
What is normal TSH?
.3 - 5 µU/mL
When do we order TSH?
Screening tool when mildly suspicious but no clinical indications.
ex treating hypothyroid decreases TG so check TSH before starting TG therapy
When do you order T3?
Check to see if T4 is converting and check on the peripheral tissues
Do you do routine TSH testing?
No, according to USPTF
What are TSH interfering factors?
Severe illness
Drugs that increase TSH levels
Drugs that decrease TSH levels
What drugs increase TSH levels?
antithyroid medications, Lithium, Potassium Iodide and TSH injection
What drugs decrease TSH levels?
Aspirin, Heparin, Steroids, T3
When would you find Reverse T3?
In hospitalized or sick patients
“sick euthyroid” syndrome.
Elevated rT3 level in a critically ill patient helps exclude a diagnosis of hypothyroidism.
Dilantin decreases rT3 due to the displacement from thyroxine-binding globulin, which causes increased rT3 clearance.
CUSHINGS
RT3 is high in patients on what drugs?
The rT3 is high in patients on propylthiouracil, ipodate, propranolol, amiodarone, dexamethasone, and the anesthetic agent halothane.
What is the reason for Graves disease?
Long acting thyroid stimulating antibodies (LATS)
What are LATS?
- Thyroid stimulating Immunoglobulins (TSI), TSH Receptor (TSHR both transactivating and blocking)
Who else has LATS?
- Subclinical hyperthyroidism
- Euthyroid patients with opthalmopathy
