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Flashcards in Hormone measurement and interpretation Deck (26)
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1

Why do we measure hormones?

Confirm clinical suspicion

Diagnose sub-clinical problems

Assess treatment (eg. efficacy and dosage)

To time procedures (eg. IVF)

Screening 

2

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

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.

3

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

TSH: low

Thyroxine: low

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

4

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

Thyroid dysfunction: high TSH

Pituitary dysfunction: low TSH

5

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

6

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

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 

7

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

Normal homeostasis

Common causes of dysfunction

Availability of test

Reliability of test

Sensitivity and specificity

Cost of test

Government regulation 

8

How are reference ranges determined?

When is this a problem?

Include 95% of a 'normal' population

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

9

Describe the factors which may cause reference intervals to vary?

Age

Sex

Race

Nutritional state

Menstrual state

Medication

 

10

What are dynamic tests?

What do they involve?

What are they used for?

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)

11

What be involved in dynamically testing an:

a) underactive gland

b) overactive gland?

a) Try to stimulate gland

b) Try to suppress gland 

12

Describe the glucose tolerance test?

Fasting patient

Give glucose at 0min

Take specimens at 0, 1 and 2 hours 

13

Describe the dexamethasone suppression test?

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)

14

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

What would be the expected result for this disease?

Cushing's syndrome

(cortisol would still be high after dexamethasone)

15

Describe the synacthen stimulation test?

What is it used to test for?

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

16

Describe the combined pituitary function test?

Why is it rarely used today?

Give insulin, TRH and LHRH 

Dangerous if too much insulin adminstered > hypoglycaemic coma

17

What is the GH stimulation test for?

Cases where there is a suspected problem with GH production

Stimulate GH release and see if it increases 

18

How are hormone levels actually measured?

Why?

Immunoassays

Present at very low levels

19

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

Competitive and Non-Competitive

20

Describe how competitive immunoassays are performed?

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 

21

How is the result of a competitive immunoassay interpreted?

Comapre signal of sample to standard curve 

More hormone binding > less labelled hormone binding > less signal 

22

Describe how a sandwich immunoassay is performed?

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 

23

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

Comapre signal of sample with standard curve

More hormone bound > higher signal 

24

How can free hormone levels be measured?

Can approximate, but very difficult to get true measurement 

25

Which types of Ab are used in immunoassays?

Describe their advantages and disadvantages?

Polyclonal: strong binding, amy lack specificity

Monoclonal: weak binding, good specificity 

26

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

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)