Flashcards in Hormone Measurement and Interpretation Deck (33)
Why measure hormones?
Confirm clinical suspicion
Diagnose sub-clinical problems
What are the approaches to measuring hormones?
Measure trophic hormone
Measure actual hormone
Measure both trophic and actual hormone
How big a change in free T4 leads to a large change in TSH?
Can a test result outside the reference range still be normal?
What can a hormone level test result vary with?
Is what is "normal" for a population the ideal?
Not always, eg: cholesterol
What are the thyroid function tests with an overactive thyroid?
What are the thyroid function tests with an underactive thyroid?
What are the thyroid function tests with pituitary underactivity?
What are the thyroid function tests in subclinical hypothyroidism?
How long can TSH take to return to normal after treatment starts in hypothyroidism?
How long can TSH and T4 take to return to normal after treatment starts in hyperthyroidism?
T4 decreases relatively quickly
TSH increases relatively slowly
What factors affect the tests used?
Common causes of dysfunction
Availability of test
Reliability of test
What is dynamic testing of hormones?
Sampling at multiple time points
Can involve stimulating/suppressing gland > see if responds appropriately
Why is dynamic testing used in subclinical disease?
Diseased system may appear to function normally under basal conditions but show abnormalities if stressed
Why is dynamic testing used to investigate abnormal results?
Is abnormal hormone result due to physiological or pathological cause?
How do you test glucose tolerance?
75 g glucose orally at 0 min
Specimens for glucose take at 0, 1, and 2 hrs
What is the effect of dexamethasone?
Strong glucocorticoid > suppresses ACTH > decreasees adrenal stimulation
How do you do a dexamethason suppression test?
Patient takes dexamethasone at midnight
Measure cortisol before and after dexamethasone
How do you do a synacthen stimulation test?
Stimulate gland with synacthen (ACTH) > measure cortisol levels
Give synacthen intramuscularly at 0 min
Blood cortisol at 0, 30, and 60 min
How is a combined pituitary function test conducted?
Give insulin, TRH, LHRH at time 0 min
Performed under medical supervision because of chance of hypoglycaemia
How is growth hormone release stimulated in a growth hormone stimulation test?
How is growth hormone release suppressed in a growth hormone suppression test?
How are hormones usually measured?
What are the types of immunoassays?
What are the principles of competitive immunoassays?
Competition between specimen hormone and added label hormone for limited amount of Ab
Increased natural hormone binding > decreased fluorescent signal
What are the steps in a competitive immunoassay?
1. Add serum and labelled hormone to Ab
3. Remove non-bound labelled hormone
4. Measure amount of label
What are the principles of sandwich immunoassays?
Ag held between 2 Abs, one of which labelled
Improved specificity as 2 binding sites used
What are the steps in a sandwich immunoassay?
1. Add serum to Ab
2. Add labelled Ab
4. Remove non-bound labelled Ab
5. Measure amount of signal
What are some problems with measuring hormones?
Different results from different labs because of different uses of standards
Poor quality of sample
Potential Ab interference
Which antibodies can interfere with immunoassays?
Human anti-mouse Abs
How is hormone measurement affected when a patient has hormone autoantibody?
Differing effects depending on type of assay and how Ab binds
AutoAb binds to naturally occurring hormone