Unit 4 - Diagnostics Flashcards
What tests detect antibody?
ELISA, SN, IFA
What tests detect agent?
PCR, sequencing, culture/VI, IFA, IHC
What is diagnostic sensitivity?
The ability to correctly identify a positive from a group of known positives
What is diagnostic specificity?
Ability to correctly identify a negative from a group of known negative samples
What factors can affect testing?
Maternal protection, vaccination history (killed, MLV, date, dose), and sentinel animals
How is the positive predictive value calculated?
True positives/ (True positives +false positives)
How is the negative predictive value calculated?
True negatives / (True negative + false negatives)
What does the positive predictive value assess?
The reliability of a positive test
What does the negative predictive value assess?
The reliability of a negative test
How is sensitivity calculated?
True positive/ (True positive + False negative)
How is specificity calculated?
True negative / (True negative + false positive)
Why/When is pooling of samples okay?
Decrease costs Slight loss of analytical sensitivity Real time PCR - amplification 1 Ct = 2 fold replication PCR expect low Ct (high concentration)
Why/When is pooling of samples not okay?
Concentration dependent
ELISAs
PCR expect high Ct (low concentration)
T/F: Cutoff points are not black and white
True
Timing of testing determines what you _______ find.
could
What are the phases of the ‘antibody responses against antigen’ curve?
Lag phase
Log phase
Plateau phase
Decline phase
T/F: Different assays have different advantages and disadvantages.
True
What is needed in order to perform virus isolation properly?
You need to know the target virus for the growth medium
What are the pros and cons to PCR?
Pros: quick, +/- quantify the amount of virus, defined window for success, can pool samples
Cons: Requires proper primers, moderate cost
What are the pros and cons to sequencing?
Pros: Are there any…?
Cons: Takes time, not cheap, shows only part of the virus, difficult to interpret
T/F: Necropsy is a diagnostic tool too.
True
