Lec 05: Diagnostic Tests in Thyroid Disorders

Question 1

T/F: Approximately 1 out of 10 Filipinos has abnormalities in their thyroid function tests (TFTs).

Answer 1

T

8.53%

Question 2

T/F: Majority of the Filipinos with TFT abnormalities have subclinical thyroid disease.

Answer 2

T

Question 3

Reasons for doing thyroid function tests EXCEPT

A. formulate a primary working impression
B. supplement physical exam findings
C. monitor clinical response to treatment
D. determine risk for malignancy
E. NOTA

Answer 3

A.

Formulation of primary working impression should be based primarily on history and PE.

Question 4

ID: What is the only available function test in the 1950s?

Answer 4

indirect estimation of thyroxine (T4)

Question 5

ID: What hormone establishes the set point in the regulation of the H-P-T axis?

Answer 5

TSH

Question 6

ID: Probable diagnosis

↓ TSH, ↑ T4, ↑ RAIU

Answer 6

Graves’ disease
hyperfunctional multinodular goiter
hyperfunctional thyroid adenoma

Question 7

True of iodide uptake

A. mediated by sodium-iodide symporter (NIS)
B. occurs at the basolateral membrane
C. extracts normally around 10-25% of serum iodide
D. A & B only
E. AOTA

Answer 7

E. AOTA

Question 8

ID: What transports iodide from the thyrocyte to the follicular lumen?

Answer 8

pendrin

Question 9

ID: This protein receptor mediates endoyctosis of thyroglobulin back into the thyrocyte.

Answer 9

megalin

Question 10

True of TSH EXCEPT

A. first line test in most clinical setting
B. may be sufficient to diagnose a patient
C. exhibits log-linear relationship with T4
D. controls the H-P-T axis
E. NOTA

Answer 10

B.

TSH is not enough to diagnose a patient. FT4 / FT3 must also be tested.

Question 11

T/F: A linear fall in FT4 produces a linear increase in TSH.

Answer 11

F

It results in LOGARITHMIC increase in TSH. (log-linear relationship)

Question 12

ID: When does TSH peak in a normal ambulatory patient?

Answer 12

between midnight to 4:00 am

Question 13

True of TSH testing

A. single determination is usually adequate
B. half-life is around 20 minutes
C. good specificity for detecting TSH secreting tumor
D. A & B only
E. AOTA

Answer 13

A.

Modest excursions, low variations in levels, and long half-life (50 mins) renders a single TSH test adequate.

Question 14

What is the concern in TSH testing in hospitalized patients?

Answer 14

Non-thyroid illnesses / co-morbidities may alter lab results.

Question 15

The following drugs increase TBG levels EXCEPT

A. estrogens
B. 5-fluorouracil
C. nicotinic acid
D. glucocorticoids
E. NOTA

Answer 15

D.

The following drugs decrease TBG

• thyroid hormones
• androgens
• anabolic steroids
• glucocorticoids
• L-asparaginase
• interleukin-6

Question 16

The following illnesses / conditions decrease TBG levels EXCEPT

A. nephrotic syndrome
B. hepatic failure
C. chronic alcoholism
D. AIDS
E. NOTA

Answer 16

D.

The following conditions increase TBG

• pregnancy
• hypothyroidism
• hepatitis
• hepatocellular carcinoma
• adrenal insufficiency
• AIDS
• angioneurotic edema

Question 17

ID: This is a specific test for Graves’ disease.

Answer 17

thyroid stimulating immunoglobulin (TSI)
- TSI is a type of TSH receptor autoantibody (TRAb)

TSI is almost never found in other autoimmune thyroid disease.

Question 18

ID: Probable diagnosis

↓ TSH, ↑ T4, ↑ RAIU, (-) TSI

Answer 18

toxic thyroid nodule

Question 19

True of thyroglobulin EXCEPT

A. only found in thyroid tissue
B. most useful as a tumor marker for recurrence
C. utilized for anaplastic thyroid cancer screening
D. measure simultaneously with anti-Tg
E. NOTA

Answer 19

C.

Anaplastic and undifferentiated thyroid cancers do not produce thyroglobulin, hence testing using Tg is not useful.

Question 20

True of thyroid peroxidase autoantibodies (TPOAb)

A. positive in Graves' disease
B. positive in Hashimoto thyroiditis
C. positive in aging individuals
D. A & B only
E. AOTA

Answer 20

E. AOTA

Sensitivity is higher though with Hashimoto thyroiditis.

Question 21

True of urine iodine content testing EXCEPT

A. utilized in iodine deficiency diagnosis in individuals
B. ingested iodine is bound to serum proteins
C. main serum protein is albumin
D. unbound iodine is excreted in urine
E. NOTA

Answer 21

A.

It is commonly utilized to diagnose iodine deficiency in POPULATIONS not in individuals.

Question 22

ID: A population is said to be iodine deficient when the median urinary iodine concentration reaches what level.

Answer 22

< 50 ug/L

Question 23

T/F: Thyroid ultrasound uses low frequency waves to for clearer imaging.

Answer 23

F

It uses high frequency waves (7.5-14.0 megahertz).

Question 24

ID: This can be used alongside UTZ to determine blood flow.

Answer 24

Doppler

Question 25

ID: This method detects around 50% prevalence of thyroid nodules.

Answer 25

autopsy palpation - 4% UTZ - 30%

Question 26

What is the usual management for unsatisfactory fine needle aspiration biopsy (FNAB) specimen? ``` A. repeat FNA with ultrasound guidance B. proceed to surgical lobectomy and biopsy C. do clinical follow up D. start therapy E. NOTA ```

Answer 26

A.

Question 27

Enumerate the four molecules used in radioisotope scans.

Answer 27

I-123 I-125 I-131 Tc-99m

Question 28

In whole body scan, where do metastatic thyroid tissue tend to localize?

Answer 28

skull and long bones

Question 29

ID: Probable diagnosis ↓ TSH, ↓ T4, ↓ RAIU, (-) TSI

Answer 29

pituitary abnormality

Question 30

Which iodine isotope produces the best image quality?

Answer 30

I-123 It also has a short half-life (0.55 d).