15. Common Immunological Lab Tests Flashcards
What is sensitivity and specifity?
Sensitivity: Ability to ID all anims TRULY pos - a test w/ 100% sensitivity will detect all pos cases
Specifity - Ability to ID all TRUE negs
a 100% will detect all neg cases
What are immunological tests?
simple to rup, rapid results, relatively inexpensive, come in a kit format, pay attention to instructions for accurate results
tests ag’s and abs
What might we collect for immunological tests and how do we handle it?
usually serum or plasma, occasionally fluids or tissues required
Use largest bore needle + appropriate V for blood
EDTA or heparin common anticoagulants
Check reqs for storage temp and sample temp when running test
Many tests have specific specimens or handling reqs
How do immunological tests work?
Based on use of Ab’s and Ags
Ab’s may be used to detect Ag’s, may measure conc of Abs specific to Ag, may use Abs to detect presence of other Abs
Tests can be quantitative - how much Ab or Ag
Tests can be qualitative - which Ag’s are present
What is direct and indirect testing?
Direct - detects Ag’s associated w/ presence of organism - pos test means Ag (virus, bact, parasite, is present)
Indirect - detects ab’s prod in response to Ag - means immune system has seen targeted Ag, does not necessarily mean bact, virus, etc is present right now
What is serology?
the science of detecting Ab’s
What are monoclonal Ab’s?
basis of immunological tests
these are antibodies identical to one another - commercially prod, prod by a single clone of plasma cells, the Ab recognizes a specific ag
Makes tests highly sensitive and specific
What are enzyme-linked immunosorbent assay?
ELISA - common immunoassay performed in vet clinics
Basis of benchtop SNAP tests
purpose: to test a sample for the presence of a specific Ag or Ab
How: test contains a monoclonal Ab that will bind to the Ag if it is present OR test contains an Ag that will bind to Ab if it is present in sample
Tests for viruses, bact, parasites, hormones, enzymes - heartworm, FeLV/FIV, parvovirus, progesterone
How does a direct elisa work?
looks for presence of Ag in sample
mAb specific to Ag is pound to filter paper
A conjugate solution is added to patient sample, solution contains more of the mAb which has been “tagged” with a dye and visible to the eye.
Patient sample and conjugate added to sample well.
If Ag present in sample, binds to mAb on test kit
remaining sample washed away in a rinse step
no color change = Ag-
Color change = Ag+
How does an indirect elisa test work?
looks for presence of Ab in a sample - specific ag bound to filter paper
Conjugate is added to sample - contains Ag that is tagged w/ dye
Sample + conjugate mixed and add to well
If Ab specific to Ag present, will bind to Ag on test kit
The unbound sample is washed away
No color change = Ab-
Color change = Ab+
What are some limitations of the indirect ELISA tests?
presence of the Ab does not necessarily mean that there is an inactive infection
Just means animal was exposed to Ag at some point
Does not differentiate btw an active infection or previous exposure
What are the controls for ELISA tests?
built into device
Control ensures: conjugate binds to whatever is being tested for, the color reagent works, can be a simple dye but may req an enzymatic reaction to activate the dye
What are ELISA SNAP tests?
simplified into a single step
designed for in-clinic use
Limitations: not quantitative - only a yes or no OR semi-quantitative (amount of Ag in control is known, so tests can determine if there is more or less than the amount in the control)
What are quantitative ELISA tests?
gives measure of amount of Ab/Ag
Dif types exists
Can make serial dilutions of sample
Can compare to quantitative controls
Competitive ELISA - Ag from patient competes w/ labelled Ag in reagent to bind w/ Ab in test kit, degree of color change corresponds w/ ag conc in sample
What is a latex agglutination immunological test?
uses sm, spherical, latex particles coated w/ ag that are suspended in water
If sample contains Ab, an Ag-Ab complex is formed which results in agglutination or clumping
uses wells or slides to contain reaction - ex blood typing or brucellosis testing in cattle
