14. Labeled Immunoassays II Flashcards
In an indirect ELISA to detect antibody to H. pylori, what would be attached to the solid phase?
An Ag, e.g. H. pylori
What would the conjugate be in an indirect ELISA to detect antibody to H. pylori?
(Anti-Human Ig) - (Enzyme) Complex
What would be attached to the solid phase in a sandwich ELISA to detect IL-2?
An Ab against IL-2
What would the conjugate be in a sandwich ELISA to detect IL-2?
(Anti-IL-2)-(Enzyme) complex
In a competitive ELISA, what is the relationship between the amount of antigen in the test sample and the resulting optical density value?
positive antigen = Low OD
negative antigen = high OD
- the results are inversely proportional
Some substrates emit light after being acted on by an enzyme. This is known as ___________________________ .
chemiluminescence
What are two advantages of ELISA methods over RIA?
- Reagents are stable
2. No special handling of reagent is required
What would the % of true positive results be in a test that has a 95% sensitivity? What is the % of false negative results?
95% True positive
5% False Negative
What would the % of true negative results be in a test that has a 95% specificity? What is the % of false positive results?
95% True Negative
5% False Positive
What is the clinical significance of the presence of an antibody to a specific antigen in a sample of patient serum?
Either:
- Person has the disease in question
- Past infection with a Ag-immunity developed
- Exposure to Ag, but not active infection-immunity developed (vaccinated)
- Biologic false positive reaction
What are some causes of false negative results in serologic tests for antibody?
- Individual may be immunosuppressed and is unable to mount a good Ab response despite having the disease
- Prozone affect = too much Ab
- Tested too soon (lag period)
