Diagnostic tests Flashcards
Why are diagnostic tests carried out?
To confirm a patient has or has had a disease
Narrow down differential diagnosis
Confirm presence of disease in a population
Quantify severity of disease in a population
If false positives are decreased, what effect does this have on false negatives?
Increases false negatives
If false negatives are decreased, what effect does this have on false positives?
Increase false positives
Sensitivity and specificity tests should be done under the same conditions. Give examples of these conditons
Same reagents
Same temperature
Same equipment
Same training of personnel
What are nomograms used for?
Detecting how probability changes based on pretest probability and likelihood ratios
What is used for pre-test probability in nomograms?
Best guess of prevalence
What do diagnostic tests imply which makes them less reliable?
Diagnostic tests work out probability of animal having disease
Don’t see if animal does or doesn’t have disease
What is sensitivity?
If D+, chance of T+
How good test is at detecting diseased animals
What is specificity?
If D-, chance of T-
How good test is at detecting non-diseased animals
What is the predictive value of a positive test (PVP)?
If T+, chance of D+
What is the predictive value of a negative test? (PVN)?
If T-, chance of D-
What is true prevalence
Number of animals with a disease
What is apparent prevalence?
Number of animals that test positive for a disease
What is test accuracy
The proportion of tests that are correct
What is the likelihood ratio?
Probability of getting a test result in a D+ compared to a D- patient
Estimates how a test result changes the odds of having a disease
