24.7 Flashcards
To screen for thyroid dysfunction, you measure ___ ___ ___ first.
Thyroid stimulating hormone
What is a dynamic test and why might you use it?
It involves sampling at multiple time points, and may involve stimulating or suppressing the gland to see if it responds appropriately
You can use it to detect subclinical disease (to stress the system) or investigate abnormal results
The “normal” for ___ tests is poorly defined.
Dynamic
Glucose tolerance test and the dexamethasone suppression test are examples of ___ tests.
Dynamic
What is the dexamethasone test?
Dexamethasone is a steroid that suppresses ACTH and therefore, suppresses cortisol production
You administer 1 mg dexamethasone at night and measure cortisol in the morning
If normal then cortisol will be low in the morning due to suppression/negative feedback
If cortisol is high in the morning, then this may be evidence of Cushing’s disease
What is the synacthen stimulation test?
Synacthen is synthetic ACTH
You give synacthen and measure cortisol at multiple time points over an hour
If low cortisol/adrenal underactivity, then there will be no cortisol result
If you suspect low GH, you can use a GH ___ test.
If you suspect high GH, you can use a GH ___ test.
If low - use a stimulation test.
If high - use a suppression test.
What are the two main types of immunoassays used for hormone measurement?
Competitive immunoassays
Non-competitive immunoassays (sandwich technique)
What is a competitive immunoassay?
Competition between specimen hormone and added labelled hormone for a limited amount of fixed antibody
If there’s more natural hormone, more will bind compared to the added labelled hormone (i.e. lower the signal from label -> higher the concentration in patient sample)
What is a non-competitive immunoassay?
Patient sample is added to a well with fixed antibodies and incubated
Then the non-bound sample is removed and a labelled antibody specific for the hormone is added (sandwiches the hormone between fixed and labelled antibodies)
If there’s more hormone in sample, there will be more label (i.e. higher the signal, higher the concentration in patient sample)
Only ___ hormone is biologically active. Most laboratory tests do not directly measure true ___ hormone - it is an estimate only!
Free - most is plasma bound!
Free hormone
(There are tests for free hormone but they are not practical!)
Polyclonal antibodies in test may bind ___, but they may lack ___.
May bind strongly
But may lack specificity and bind to similar molecules
Monoclonal antibodies may have good ___, but they may bind ___.
Good specificity, but may bind weakly
Patients with heterophilic antibodies?
Maybe the patient has anti-mouse antibodies
If anti-mouse antibodies are used for the test assay, there will be a falsely high result
If lab results do not match the clinical picture, then question the ___
RESULT
There can be errors
