Hormone measurement and interpretation Flashcards
Why do we measure hormones?
Confirm clinical suspicion
Diagnose sub-clinical problems
Assess treatment (eg. efficacy and dosage)
To time procedures (eg. IVF)
Screening
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.
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.
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
Compare the TSH and thyroxine levels for overactive thyroid, underactive thyroid and pituitary underactivity?
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
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
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
Describe the factors which may cause reference intervals to vary?
Age
Sex
Race
Nutritional state
Menstrual state
Medication
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)
What be involved in dynamically testing an:
a) underactive gland
b) overactive gland?
a) Try to stimulate gland
b) Try to suppress gland
Describe the glucose tolerance test?
Fasting patient
Give glucose at 0min
Take specimens at 0, 1 and 2 hours
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)
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)
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