HORMONES

Question 1

What is the key to thyroid hormone synthesis ? Why ?

Answer 1

• serum IODIDE is trapped in thyroid and incorporated into tyrosine
• iodine transport into follicles is a rate-limiting step

Question 2

How are thyroid hormones produced ?

Answer 2

• thyrotropin releasing hormone (TRH) is secreted from hypothalamus in response to low T3 and T4
• TRH stimulates production of TSH in the anterior pituitary
• TSH binds to follicular cells of thyroid = secretion of triiodothyronine (T3), thyroxine (T4)*, and reverse T3

Question 3

What is the major secretory product of the thyroid ?

Answer 3

thyroxine (T4)

Question 4

How do T3 and T4 circulate in the blood ?

Answer 4

Bound to thyroid binding globulin (TBG)*, transthyretin, and albumin

*TBG has the greatest affinity for T4

Question 5

How are T3 and T4 regulated ?

Answer 5

• free T4 is deiodinated in the liver = active T3
• T3 regulates rate of cellular oxidation (uptake of glucose) and protein metabolism
• increased T3 and T4 inhibit anterior pituitary response to TRH
• decreased thyroid hormones cause increase in TRH and TSH secretion

Question 6

List 2 thyroid autoimmune diseases

Answer 6

1. Graves’ disease; formation of autoantibodies specific to the TSH receptor = hyperthyroidism
2. Hashimoto; cell-mediated autoimmunity causing thyroid dysfunction (goitre, thyroiditis, frequently hypothyroidism)

Question 7

Endogenous Hypothyroidism

Answer 7

• aka Hashimoto thyroiditis
• autoimmune thyroid disease

Question 8

Exogenous hypothyroidism

Answer 8

• Graves’ disease
• associated with iodine imbalance and various medications

Question 9

Secondary hypothyroidism

Answer 9

Due to damage/disease of hypothalamus/ pituitary gland

Question 10

Endogenous hyperthyroidism

Answer 10

• aka Graves’ disease
• associated with thyroid tumors and disorders of hypothalamus/ pituitary gland

Question 11

Exogenous hyperthyroidism

Answer 11

• associated with viral and bacterial thyroiditis

Question 12

Describe Non-thyroidal Illness (NTI)

Answer 12

• low total and free T3; elevated REVERSE T3; normal to low TSH
• seen in starvation, sepsis, surgery, myocardial infarction, diabetes…
• lack of conversion of T4 to T3 at the tissues
• suppresses TRH release, reduced T3 and T4 turnover, reduction of T3 at liver, tissue-specific down-regulation of receptors, transporters, and enzymes

Question 13

What is the most sensitive and specific test for the investigation and management of primary thyroid dysfunction ?

Answer 13

TSH testing; in comparison with T4, TSH is not markedly affected by NTI or drugs

Question 14

Which subunit of hCG is specific to the placenta ?

Answer 14

β* = specific to placenta

α = TSH, LH, and FSH

Question 15

What does hCG do ?

Answer 15

hCG acts on corpus luteum to produce progesterone until placenta can produce enough progesterone to maintain pregnancy

Question 16

Clinical application of qualitative hCG serum

Answer 16

Used to diagnose pregnancy

Question 17

Clinical Applications of Quantitative serum/ plasma hCG

Answer 17

• date pregnancy
• detect multiple pregnancies (2X in twins)
• assist in detection of ectopic pregnancies

Question 18

Clinical Applications of increased intact hCG and free β subunit

Answer 18

• Trophoblastic disease
• Germ cell tumours
• Other cancers (biliary, pancreatic)

Question 19

What is used to monitor treatment and progression of trophoblastic disease ?

Answer 19

Serial measurement of hCG

Question 20

What is First Trimester Screening used for ?

Answer 20

• determine risk of having a fetus with serious birth defects
  Ie. Neural tube defect or Down’s Syndrome
• performed between 10 to 13 weeks’ gestation

1. hCG in blood = increased
2. pregnancy associated plasma a protein A = increased
3. Nuchal Translucency Test = increased nuchal space

Question 21

What results in the First Trimester Screening would indicate a Trisomy ?

Answer 21

1. hCG in blood = increased
2. pregnancy associated plasma a protein A = increased
3. Nuchal Translucency Test = increased nuchal space

Question 22

What is the Second Trimester Screen ?

Answer 22

• aka Multiples of the Median/ Quad Screen
• prenatal testing to estimate risk of open spina bifida, anencephaly, trisomy 21 and trisomy 18

1. Alpha-fetoprotein (AFP) = increased
2. Human chorionic gonadotropin (hCG) = increased
3. Unconjugated estriol 3 = increased
4. Dimeric Inhibin A = increased

Question 23

What results in the Second Trimester Screening would indicate fetal abnormality ?

Answer 23

1. Alpha-fetoprotein (AFP) = increased
2. Human chorionic gonadotropin (hCG) = increased
3. Unconjugated estriol 3 = increased
4. Dimeric Inhibin A = increased

Question 24

What is MoM ?

Answer 24

• multiple of the median
• statistical value measures how different patient results is from the median of a similar population
• patients with a greater MoM result than the cut-off value will have additional testing

Question 25

T or F: The cut-off MoM value does NOT have a 100% positive or negative predictive value

Answer 25

TRUE; The cut-off MoM value does NOT have a 100% positive or negative predictive value