Endocrinology Thyroid and Adrenal Flashcards
Where is TRH made?
TSH release is related to?
Thyroid makes T3 or T4 in higher amounts?
Most T3 made under normal conditions?
Hypothalamus at relatively constant rate
Concentration of cellular T3; at least 50% of pituitary T3 produced in cell from T3
T4 and when TSH high iodine rate limiting causing more T3 to be made
Liver
In non-thyroidal illness what are the T3 and T4 and TSH levels?
Most important test of thyroid function?
How is TSH measured, pitfall in pituitary disease?
Low T3, normal T4 and TSH
TSH; changed in logarytmicall with T4/T3; must destinguish from low normal from supressed (<0.05 mIU/L)
Immunoassay; pituitary makes abnormal TSH with reducted bio activity but enhanced Immunoassy; TSH ~15% high normalized with T4 administration
Is total T4, T3 still used?
TBG estimation?
Yes, normal rules out thyroid disease; need to estimate total binding protein by TBG estimation
Look at residen uptake vs T-uptage: Add excess T3 and fills are the binding protein sites–> add resing ot bind all the residual T3–> wash–> count resin and see how much is on resin
Less on resin=more free protein
More on Resin= less free protein
If change in same direction, thyroid problem, if change in opposite problem in TBG
Gold standard for Free T4 measurement?
False results in what patient states?
Anti-TPO seen in?
TSH receptor antibody seen in?
TSI is a test for?
Equilibrium dialysis; hard to measure free T4 due to small amount free
Acute illness and pregnancy
Anti-TPO; Graves’ and Hashimoto’s
TSH receptor antibody: Graves (stimulatory), atrophic thyroditis (blocking)
TSI: Graves, measure cAMP when thyroid cells incubated with patients IgG
When is Thyroglobulin tested for?
What is Anti-TG, lack of TG implies?
After cancer removal for residual disease (post TSH stimulation)
Anti-Thyroglobulin; interferars with immunoassay; so test for Ab’s when testing for TG!!
Lack of anti-TG implies lack of TG (no tumor)
First lab finding in hyperthyroidism?
What goes up first T3 or T4?
T4, T3, T3RU?
What normalizes first?
Low TSH; “Hot nodule”
T3 before T4
All high!
T4 normalizes first then T3 TSH may takes months before coming back up
What lab goes up 1st in hypothyroidism?
T3, T4, T3 RU, total?
Most common cause, other causes?
TSH!
All low; 30-40% have normal T3
Not having a thyroid (surgery, post radioiodine) Hashimotos; check Anti-TPO and Anti-TSH receptors in adults
Acute illness effects thyroid tests how?
Pregnancy/OC effects thyroid tests how?
Other causes of high TBG?
Causes of low TBG, labs?
Acute illness: low T3 (low peripheral conversion), normal Total/FreeT4 and TSH
Estrogen increases TBG: High total T4 and T3, low T3RU (most sites filled), normal TSH and Free T4
Opiates, active liver injury, pregnancy and OC pills
Cirrhosis/nephrotic syndrome, congenital deficiency, low total T3/T4, high T3RU (due to lwo TBG), normal TSH and Free T4
What regulated the Glucororticoids?
Highest production when?
What causes an increases?
What drug inhibits?
Hypothalamic CRH and pituitary ACTH
Morning
Stress, IL-6, serotonin
Cortisol only endogenous steroid inhibiting ACTH
What makes measuring Cortisol hard?
What is urine free cortisol?
Diurnal changes, highest (5-25 ug/dL) in morning and low (1-7 ug) early sleep
Some synthetic steroids cross react
Protein bound; free measurements not commonly used
Urine free: When binding capcity exceeded increases exponentially in urine, most sensitive direct test of cortisol production; HARD, needs 24 hour collection
What is a better way to measure cortisol since urine sucks?
When to check?
Why not used much?
Saliva measurements: proportional to plasma free
Easy to collect and best to be checked at bed time
Only available at reference labs
Problems with measuring ACTH?
What are suppression tests for ACTH?
Low vs high suppression tells us?
Released in bursts; unstable; difficult to interpert
Supression: Give dexamethasone (should supress ACTH and cortisol)
Look at dose to decrease plasma cortisol; Low dose supression= Cushings syndrome (high cortisol)
High dose suppresion= Cushings Dx (ACTH increase from pituitary adenoma)
What does Cortrysun stimulation test for?
How does insulin hyperglycemia test work?
How does Metyrapone test work (boards love this)?
See if patient can respond to ACTH; use synthetic fragment ACTH; see if cortisol goes up
No response means adrenal is no longer functional
Pituitary: Insulin hypoglycemia: most sensitive, rarely used, normal cortisol response >18 ug/dL
Metyrapone: Blocks 11-hydroxylase (last step in cortosol production) normal response is cortisol falling but ACTH and 11-deoxycortisole rise (at least 7ug/dL)
What causes Cushing’s?
Symptoms?
Most common cause?
Other causes
Increased cortisol/androgen
Obesity, hypertension, poor would healing, hypokalemia (some mineral activity), alkalosis, acne, hirsutism, etc.
Pituitary ACTH overproduction (Cushing dx); 70%
Adreanal adenoma/carcionoma: 15%
Ectopic ACTH (Small cell lung and carcinoid and thymoma): 15%
New gold standard test for ACTH/Cushing Dx measurement?
Inferior petrosal sinus sampling of ACTH after CRH administration: better than high dose DST
