Hormone Measurement and Interpretation Flashcards
Why measure hormones?
Confirm clinical suspicion Diagnose sub-clinical problems Assess treatment Time procedures Screening
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?
Small change
Can a test result outside the reference range still be normal?
Yes
What can a hormone level test result vary with?
Age Sex Race Nutritional state Menstrual state Medication Person
Is what is “normal” for a population the ideal?
Not always, eg: cholesterol
What are the thyroid function tests with an overactive thyroid?
Decreased TSH
Increased T4
What are the thyroid function tests with an underactive thyroid?
Increased TSH
Decreased T4
What are the thyroid function tests with pituitary underactivity?
Decreased TSH
Decreased T4
What are the thyroid function tests in subclinical hypothyroidism?
Normal T4
Elevated TSH
How long can TSH take to return to normal after treatment starts in hypothyroidism?
4-6 weeks
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?
Normal homeostasis Common causes of dysfunction Availability of test Reliability of test Sensitivity, specificity Cost Government regulation
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?
Fasting patient
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?
Exercise
Hypoglycaemia
Arginine
How is growth hormone release suppressed in a growth hormone suppression test?
Elevated glucose
How are hormones usually measured?
Immunoassays
What are the types of immunoassays?
Competitive
Non-competitive (sandwich)
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?
- Add serum and labelled hormone to Ab
- Incubate
- Remove non-bound labelled hormone
- 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?
- Add serum to Ab
- Add labelled Ab
- Incubate
- Remove non-bound labelled Ab
- 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?
T3/T4 autoantibodies
Heterophile Abs
Human anti-mouse Abs
Rheumatoid factor
How is hormone measurement affected when a patient has hormone autoantibody?
Rare
Differing effects depending on type of assay and how Ab binds
AutoAb binds to naturally occurring hormone
How is hormone measurement affected when a patient has heterophilic antibody?
Falsely high results because links reaction Abs
