ATA 2016 Hypothyroidism

Question 1

Participates in the clearance of both serum T4 and T3
A. Type 1 deiodinase
B. Type 2 deiodinase
C. Type 3 deiodinase
D. Type 4 deiodinase

Answer 1

C.Type 3 deiodinase

Question 2

Approximate amount of T4 secreted daily

Answer 2

85 mcg

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Question 3

Gastrointestinal absorption of the tablet formulation of LT4 is in the range in healthy fasting adults

Answer 3

70%–80%

Question 4

Half life of T4

Answer 4

7 days

Question 5

Steady-state levels of T4 and TSH are generally achieved in how many weeks

Answer 5

6 weeks

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Question 6

Most reliable marker of adequacy of replacement treatment

Answer 6

TSH

Question 7

Therapeutic target for TSH in hypothyroid patients

Answer 7

0.4–4.0 mIU/L

Question 8

Although no RCTs are currently available, a recent meta- analysis showed that significantly increased risk of cardiovas- cular mortality and morbidity was primarily observed in indi- viduals with TSH levels of

Answer 8

> 10 mIU/L

Question 9

Absorption of LT4 occurs where

Answer 9

jejunum and ileum

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Question 10

LT4 absorption cAn be decreased by

Answer 10

1. Food
2. Fiber , soy products
3. Espresso coffee-> sequesters LT4

(Page 1681)

Question 11

Because co-administration of food and levothyroxine is likely to impair levothyroxine absorption, it is recommend that, if possible, levothyroxine be taken at what times?

Answer 11

60 minutes before breakfast or 3 or more hours after evening meals

(1681)

Question 12

What are the medications and supplements that should not be co-administered with levothyroxine in order to avoid impaired absorption?

Answer 12

calcium carbonate

PPIs

bile acid sequestrants

ferrous sulfate

aluminum-containing antacids

sucralfate

Question 13

What are gastrointestinal conditions that should be considered when a patient’s levothyroxine dose is much higher
than expected

Answer 13

1. Helicobacter pylori–related gastritis
2. Atrophic gastritis
3. celiac disease
4. Lactose intolerance
5. Intestinal giardasis

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Question 14

Aside fromgastrointestinal conditions what are other conditions that may affect LT4 requirement

Answer 14

1. Extreme Obesity

2. Advancing age (35)

Question 15

What medications may alter a patient’s levothyroxine requirement by affecting either metabolism or binding to transport proteins

Answer 15

Estorgen and Androgens

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Phenobarbital, phenytoin, carbamazepine, rifampin, sertraline
(May need increased dosing)

Tyrosine kinase inhibitors
(Substantially increased doses)
Ie imatinib, motesanib, sorafanib

Amiodarone ,Growth hormone replacement

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Amiodadone

Question 16

Mechanism by which tyrosine kinase inhibitors increase the LT4 requirement in hypothyroid pa- tients

Answer 16

Accelerated conver- sion of T3 to rT3 because of activation of D3

Question 17

An increase in LT4 doses may be needed in patients with amiodarone due to what mechanisms?

Answer 17

+ inhibition of D2 in rodents
+ iodine content

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Question 18

An increase in LT4 doses may be needed in patients with Vascular tumors , fibroblastic tumors , and gastroin- testinal stromal tumors due to?

Answer 18

Overexpression of D3

Question 19

Examples of drugs that increase serum TBG
from insignificant to significant degrees (increase total T4 levels ->TSH levels may rise above the reference range ->need for a higher dose of LT4)

Answer 19

estrogen
tamoxifen
raloxifene
clofibrate
opioids 
mitotane 
fluorouracil
capecitabine

Question 20

Examples of drugs that decrease serum TBG

Answer 20

Androgen

Question 21

What factors determine the levothyroxine dose required by a hypothyroid patient
for reaching the appropriate serum TSH goal?

Answer 21

weight
lean body mass
pregnancy status, aetiology of hypothyroidism
degree of thyrotropin elevation
age
general clinical context, including the presence of cardiac disease