Lab assays Flashcards
accuracy vs precision?
accurate tests get close on average to the right answer, precise tests have consistently reproducible results (may not necessarily be “correct” though)
Which test property most influences test performance with…low organism burden?
sensitivity
Which test property most influences test performance with…potential detection of closely related organisms?
specificity
Which test property most influences test performance with…too little specimen?
sensitivity
Which test property most influences test performance with…low prevalence population?
specificity
Pros/cons of microscopy?
Pros: low cost, rapid results
Cons: what you see is what you get
Culture pros/cons?
Pros: recovery of live organisms, higher specificity than microscopy
Cons: requires specialized media, incubator etc, lower specificity than NAATs, and some bugs can’t be cultivated in vivo
Viral culture issues?
requires host cells, $$$, special labor, equipment, and training
How does a blood culture work?
- blood drawn and split into 2 bottles (1 set)
- 2 sets overall taken from 2 different body sites to confirm there is no contamination
- when results from both sets are the same, source is organism in patient’s blood
How are antibody detection tests/serology retrospective?
Because we form antibodies in response to infection. If you’re detecting antibodies to a certain organism/pathogen, that infection happened in the past.
Antigen detection tests look for what?
the presence of the organism in the specimen
Direct fluorescence microscopy assays are an example of what kind of testing?
antigen detection test
Rapid stress tests fall under what category of testing?
antigen detection test
Particle agglutination tests fall under what category of testing?
antigen detection test
Explain how NAATs work.
enzymatically amplify target viral DNA/RNA molecules (i.e. by PCR, rtPCR, or other techniques)
Pros of NAATs?
highly sensitive (compared to microscopy, cultures, or antigen detection) and more specific for nucleotide sequences, doesn’t require live organisms
Exponential amplification refers to?
millions of copies of a template molecule that can be amplified quickly using NAATs
Potential shortfall of NAATs?
high sensitivity can pick up dead organisms - may lead you to believe there’s an ongoing infection when abx have actually killed organisms
Explain how NAATs can lead to less invasive testing
Example of STDs - sensitivity of NAATs is so high that you can take use a urine sample instead of an invasive/uncomfortable endocervical or urethral swab
Set up needed for antimicrobial susceptibility tests?
in vitro test with live organisms grown in presence of antimicrobial agents; may find genetic basis of resistance
