Hormone measurement and interpretation

Question 1

Why do we measure hormones?

Answer 1

Confirm clinical suspicion

Diagnose sub-clinical problems

Assess treatment (eg. efficacy and dosage)

To time procedures (eg. IVF)

Screening

Question 2

Describe the expected TSH and thyroxine levels in a patient with hypothyroidism due to thyroid gland dysfunction? Explain.

Answer 2

TSH: high

Thyroxine: low

Thyroid gland is damaged, and not making thyroxine. Feedback to pituitary increases TSH production to try to stimulate the thyroid gland.

Question 3

Describe the expected TSH and thyroxine levels in a patient with hypothyroidism due to pituitary dysfunction? Explain.

Answer 3

TSH: low

Thyroxine: low

Pituitary is abnormal, so producing low amounts of TSH. Therefore, not much stimulation for thyroid to produce thyroxine > low thyroxine.

Question 4

How can we tell the difference between hypothyroidism due to thyroid gland dysfunction and hypothyroidism due to pituitary dysfunction?

Answer 4

Thyroid dysfunction: high TSH

Pituitary dysfunction: low TSH

Question 5

Compare the TSH and thyroxine levels for overactive thyroid, underactive thyroid and pituitary underactivity?

Answer 5

Question 6

Describe the progression of TSH and FT4 levels with a faling thyroid gland?

Answer 6

FT4 may drop slightly

TSH very sensitive to any change in FT4 > TSH rapidly increases

So, TSH can be high when FT4 is normal pre-clinically

As FT4 begins to fall, TSH continues to rise

Question 7

Describe the factors affecting the tests used to assess hormone levels?

Answer 7

Normal homeostasis

Common causes of dysfunction

Availability of test

Reliability of test

Sensitivity and specificity

Cost of test

Government regulation

Question 8

How are reference ranges determined?

When is this a problem?

Answer 8

Include 95% of a ‘normal’ population

Problem: may be a difference between what is normal for a population and what is ideal

Question 9

Describe the factors which may cause reference intervals to vary?

Answer 9

Age

Sex

Race

Nutritional state

Menstrual state

Medication

Question 10

What are dynamic tests?

What do they involve?

What are they used for?

Answer 10

Sampling at multiple time points

May involve stimulating or suppressing a gland to see if it responds appropriately

Used to assess subclincial disease (diseased system may appear to function normally but may show abnormalities under stress) or investigating abnormal results (determine whether the result is due to a physiological or pathological cause)

Question 11

What be involved in dynamically testing an:

a) underactive gland
b) overactive gland?

Answer 11

a) Try to stimulate gland
b) Try to suppress gland

Question 12

Describe the glucose tolerance test?

Answer 12

Fasting patient

Give glucose at 0min

Take specimens at 0, 1 and 2 hours

Question 13

Describe the dexamethasone suppression test?

Answer 13

Patient takes dexamethasone a midnight > should supress normal adrenal production of cortisol

Measure cortisol before and after dexamethasone

Expect low cortisol (if high, require further investigation)

Question 14

A dexamethasone test would be used for suspicion of which disease?

What would be the expected result for this disease?

Answer 14

Cushing’s syndrome

(cortisol would still be high after dexamethasone)

Question 15

Describe the synacthen stimulation test?

What is it used to test for?

Answer 15

Used to test for adrenal underactivity

Stimulate adrenal gland with ACTH and meausre cortisol levels at 0, 30 and 60 mins

Expect cortisol levels to rise with stimulation

Question 16

Describe the combined pituitary function test?

Why is it rarely used today?

Answer 16

Give insulin, TRH and LHRH

Dangerous if too much insulin adminstered > hypoglycaemic coma

Question 17

What is the GH stimulation test for?

Answer 17

Cases where there is a suspected problem with GH production

Stimulate GH release and see if it increases

Question 18

How are hormone levels actually measured?

Why?

Answer 18

Immunoassays

Present at very low levels

Question 19

What are the two types of immunoassays that can be performed?

Answer 19

Competitive and Non-Competitive

Question 20

Describe how competitive immunoassays are performed?

Answer 20

Limitied amount of Ab fixed in tube

Labelled hormone added in known amount, as well as natural hormone in blood

Competition for limited binding sites on Ab > amount of natural hormone bound should be proportional to amount in patient serum

Question 21

How is the result of a competitive immunoassay interpreted?

Answer 21

Comapre signal of sample to standard curve

More hormone binding > less labelled hormone binding > less signal

Question 22

Describe how a sandwich immunoassay is performed?

Answer 22

Ab added in excess

Labelled 2nd Ab added in excess, as well as natural hormone in blood

Hormone held between 2 Ab > measure amount of signal

Question 23

How are the results of a non-competitive/sandwich immunoassay interpreted?

Answer 23

Comapre signal of sample with standard curve

More hormone bound > higher signal

Question 24

How can free hormone levels be measured?

Answer 24

Can approximate, but very difficult to get true measurement

Question 25

Which types of Ab are used in immunoassays? Describe their advantages and disadvantages?

Answer 25

Polyclonal: strong binding, amy lack specificity Monoclonal: weak binding, good specificity

Question 26

Describe some of the problems associated with using immunoassays to detect hormone levels?

Answer 26

Ab specificity (may cross-react with similar looking Ag) Standardisation (different results from different labs) Sample quality and stability (some analytes very temperature sensitive or require preservatives) Patient with hormone auto-Ab Patient with heterophilic Ab (can get falsely high results if heterophilic Ab links reaction Abs instead of hormone linking them)