Diagnostic Tests Flashcards
Diagnosis
Classify animals as having a disease or not
What are the uses of diagnostic tests
Clinical medicine: used for treatment and prognosis
Surveillance: identify changes in disease status in a population
International trade: keep infected animals out
Research: identify and monitor research subjects
Dichotomous
only two possible aniswers
Continuous
a continuum of possible answers
E.g. Serum chemistry, antibody titers, CBC
Hematology diagnostic tests
Measures amount of different cell types in a venous blood sample
Biochemical diagnostic tests
Measures enzymes, metabolites, proteins - usually in venous sample
Immunological diagnostic tests
use antigen to measure antibodies
Pathogen detection tests
detect the pathogen itself or specific parts of it
True Positive
Diseased animal that tests positive
True negative
non-diseased animal that tests negative
False negative
diseased animal that tests negative
False Positive
Non-diseased animal that tests positive
Sensitivity
the proportion of diseased animals that the test correctly classifies as positive
Specificity
the proportion of non-diseased animals that the test correctly classifies as negative
Sensitive Test
rules disease OUT
Specific test
rules disease IN
When do you maximize sensitivity?
when you need to detect all disease or infected animals
When do you maximize specificity?
when the cost of a false positive is high and you don’t care if there are a lot of false negatives
Positive Predictive value
The predictive value of a positive result
Negative predictive value
the predictive value of a negative test result
Sensitivity Calculation
Number of test positive/Number diseased
Specificity calculation
Number of test negative /number non-diseased
PPV calculation
Number of diseased/Number test positive
NPV Calculation
number of non-diseased/number test negative
