Diagnostic Tests

Question 1

Diagnosis

Answer 1

Classify animals as having a disease or not

Question 2

What are the uses of diagnostic tests

Answer 2

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

Question 3

Dichotomous

Answer 3

only two possible aniswers

Question 4

Continuous

Answer 4

a continuum of possible answers

E.g. Serum chemistry, antibody titers, CBC

Question 5

Hematology diagnostic tests

Answer 5

Measures amount of different cell types in a venous blood sample

Question 6

Biochemical diagnostic tests

Answer 6

Measures enzymes, metabolites, proteins - usually in venous sample

Question 7

Immunological diagnostic tests

Answer 7

use antigen to measure antibodies

Question 8

Pathogen detection tests

Answer 8

detect the pathogen itself or specific parts of it

Question 9

True Positive

Answer 9

Diseased animal that tests positive

Question 10

True negative

Answer 10

non-diseased animal that tests negative

Question 11

False negative

Answer 11

diseased animal that tests negative

Question 12

False Positive

Answer 12

Non-diseased animal that tests positive

Question 13

Sensitivity

Answer 13

the proportion of diseased animals that the test correctly classifies as positive

Question 14

Specificity

Answer 14

the proportion of non-diseased animals that the test correctly classifies as negative

Question 15

Sensitive Test

Answer 15

rules disease OUT

Question 16

Specific test

Answer 16

rules disease IN

Question 17

When do you maximize sensitivity?

Answer 17

when you need to detect all disease or infected animals

Question 18

When do you maximize specificity?

Answer 18

when the cost of a false positive is high and you don’t care if there are a lot of false negatives

Question 19

Positive Predictive value

Answer 19

The predictive value of a positive result

Question 20

Negative predictive value

Answer 20

the predictive value of a negative test result

Question 21

Sensitivity Calculation

Answer 21

Number of test positive/Number diseased

Question 22

Specificity calculation

Answer 22

Number of test negative /number non-diseased

Question 23

PPV calculation

Answer 23

Number of diseased/Number test positive

Question 24

NPV Calculation

Answer 24

number of non-diseased/number test negative