Hormone Measurement and Interpretation

Question 1

What is the reference range for free thyroxine?

Answer 1

9-25pmol/L

Question 2

What is the reference range for TSH?

Answer 2

0.4-4.7 mIU/L

Question 3

What is measured to determine thyroid function and why?

Answer 3

TSH (medicare covered), first to show abnormality; if the thyroid is failing TSH will elevate (pituitary is sensitive) before FT4 starts to fall - can pick up disease process in preclinical stages

Question 4

What are static tests?

Answer 4

Measuring at one time point reflecting what is going on with the patient at that specific time

Question 5

What are dynamic tests?

Answer 5

Taking multiple samples across multiple time points especially when treating someone to see the effects eg stimulating or suppressing and endocrine gland and measuring the response of that gland

Question 6

What are the main uses of dynamic tests?

Answer 6

Looking for subclinical disease that has normal function under basal conditions but becomes apparent when the system is stressed; investigating abnormal response for physiological vs pathological causes

Question 7

What is the use of the glucose tolerance test?

Answer 7

Gold standard for determining diabetes based on response to a glucose load - in diabetes blood sugar will spike higher and take longer to resolve

Question 8

What is the use of the dexamethasone suppression test?

Answer 8

Assessing pituitary and adrenal involvement in hypercortisolism - taken at midnight, should cause pituitary to stop producing ACTH (tf -cortisol); if cortisol is still high, may have Cushing’s syndrome

Question 9

What is the reference range for basal serum cortisol?

Answer 9

250-750nmol/L

Question 10

What is the post-dexamethasone serum cortisol?

Answer 10

<150nmol/L

Question 11

What is the use of the synacthen stimulation test?

Answer 11

Determining adrenal underactivity by stimulating it with ACTH (synACTHen) and measuring cortisol at 30 and 60min

Question 12

What is the use of the combined pituitary function test?

Answer 12

Looking at all pituitary hormones by giving insulin (drops glucose levels to simulate stress and induce ACTH and subsequent cortisol production), TRH (increase TSH levels and some effect on prolactin), and LHRH (increases LH and FSH) - can be dangerous (hypoglycaemia) therefore it requires medical supervision and is rarely done

Question 13

What is the use of the growth hormone stimulation test?

Answer 13

Usually done in children, where GH production is suspect - stimulate GH production (exercise, hypoglycaemia, arginine insulin test)

Question 14

What is the use of the growth hormone suppression test?

Answer 14

excessive growth/acromegaly - suppress GH, usually with a GTT because GH is suppressed by high glucose levels (ie ILGFs)

Question 15

What are the two types of immunoassays used to measure hormones?

Answer 15

competitive and non-competitive (sandwich technique)

Question 16

What are the principles of competitive hormone immunoassay?

Answer 16

using a limited amount of Ab to hormone, add known amount of labelled hormone and patient serum hormone; the hormones will compete for the Abs - low signal means high serum/natural hormones where high signal means low serum/natural hormones (high labelled hormone binding)

Question 17

What are the principles of non-competitive (sandwich) hormone immunoassay?

Answer 17

excess of one Ab in tube, add patient serum (natural hormone), add excess of a 2nd Ab that is labelled and binds a different site on the hormone (greater specificity) - high signal means high serum/natural hormone where low signal means low serum/natural hormone

Question 18

How are free hormone levels measured?

Answer 18

difficult to measure; use machines

Question 19

What are polyclonal antibodies?

Answer 19

bind to many sites of the hormone (strong binding, low specificity)

Question 20

What are monoclonal antibodies?

Answer 20

one antibody specific to one part of a hormone

Question 21

What are some problems with immunoassay methods?

Answer 21

cross-reactivity of antibody to similar-looking antigens (eg cortisol and other steroids); standardization (internationally, across labs, and manufacturers); quality of sample (hormones are temperature sensitive); patient hormone autoantibodies or heterophilic antibodies (eg antimouse antibodies react with the mouse proteins of the assay antibody)