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RUSVM Epidemiology > Diagnostic Tests > Flashcards

Diagnostic Tests Flashcards

1
Q

diagnosis

A

classify animals as having a disease (or other health related state) or not

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2
Q

uses of diagnostic tests

A

clinical medicine: treatment and prognosis

surveillance: identify changes in disease status

international trade: keep infected animals out

research: identify and monitor research subjects

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3
Q

Dichotomous tests

A

only 2 possible answers

positive or negative

e.g radiographs, MRI, PM

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4
Q

continuous tests

A

continuum of possible answers, still need to classify as positive or negative

e.g serum chemistry, antibody titers, CBC

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5
Q

hematology diagnostic tests

A

measures amount of different cell types in a venous blood sample

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6
Q

biochemical diagnostic tests

A

measures enzymes, metabolites, proteins, etc-usually in venous blood sample

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7
Q

immunological diagnostic tests

A

use antigen to measure antibodies or vice versa

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8
Q

example of immunologic tests

A

SNAP FIV/FeLV

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9
Q

pathogen detection tests

A

detects the pathogen itself (or specific parts of it)

ex: microscopy, culture, virus isolation, PCR

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10
Q

T/F some test for epidemiological investigations “fingerprint” pathogens or discriminate infected from vaccinated animals (DIVA)

A

true

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11
Q

T/F usually cant measure the disease itself

A

true

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12
Q

what is measured?

A

‘something’ (chemical, antigen, etc) that is present in a certain quantity when an animal has a certain disease/underlying pathogen

test value

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13
Q

how do diagnostic tests work?

A

sample taken –> test is run and test value is produced –> decision i (+/-) is made by test or diagnostician (test result)

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14
Q

cut off value

A

determine experimentally as the value that minimizes false positive/ false negative results

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15
Q

T/F usually there is a clear separation in the test values between diseased and non diseased

A

false

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16
Q

T/F some non-diseased animals may have higher test values than some of the disease and vice versa

A

true

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17
Q

T/F can have false positives/negatives

A

true

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18
Q

True positive

A

diseased animal that tests positive

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19
Q

true negative

A

non-diseased animal that tests negative

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20
Q

false negative

A

diseased animal that test negative

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21
Q

false positive

A

non-diseased animal that tests positive

22
Q

how are gold standard tests used

A

true disease status of individuals is often determined using a gold standard test, against which the performance of a new test is evaluated

23
Q

disadvantages of gold standard test

A

labor intensive, impractical, highly invasive, slow and/or expensive

24
Q

every test is evaluated by how accurately it classifies:

A

diseased individuals as test positive

non-diseased individuals as test negative

25
Q

how to evaluate a test

A

test group of disease animals

test a group of non-diseased animals

establish a cut-off value

26
Q

what are the 2 parameters to evaluate diagnostic test

A

sensitivity (Se)

Specificity (Sp)

27
Q

diseased animals are used to determine

A

sensitivity (of the new test)

28
Q

non diseased animals are used to determine

A

specificity (of the new test)

29
Q

T/F Se and Sp are proportions

A

true

30
Q

determining sensitivity

A

test a group of diseased animals

proportion of diseased animals that the test correctly classifies as positive

31
Q

what are some factors that can cause sensitivity to be low?

A

few/small amounts of whatever the test measures

samples are degraded before testing

32
Q

T/F a sensitivity of 100% has no false negatives

A

true

classifies all diseased animals as positive

33
Q

In a low Se test (75%)

A

25% of diseased not detected and are false negatives

34
Q

T/F Se doesn’t tell us anything about how well the test performs on non-diseased animals

A

true

35
Q

determining Sp

A

test a group of non-diseased animals

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

36
Q

what are some factors that can cause specificity to be low?

A

cross-reactivity (mistakenly identified as another)

samples are contaminated

37
Q

T/F high SP (100%) has no false positives

A

true

correctly classifies all non-diseased animals as negative

38
Q

in a low Sp test (75%)

A

25% of non- diseased animals classified as positive (false positive)

39
Q

T/F Sp doesnt tell you anything about how well the test performs on diseased animals

A

true

40
Q

what is a balanced test

A

Equal Se and Sp

equally misclassifies diseased and non-diseased

41
Q

SnNOut

A

sensitive test when Negative rules disease Out

correctly classifies ALL diseased animals as POSITIVE

42
Q

SpPIn

A

Specific test when Positive rules disease in

remember-looks at non-diseased animals so if positive can’t rule it out

43
Q

T/F test with 100% sensitivity will have no false negatives but may have false positives if Sp is low

A

true

any negative results are from non-diseased animals

44
Q

T/F test with 100% specificity will have no false positive results but may have false negatives with low Se

A

true

any positive results are from diseased animals (rules it in)

45
Q

maximize sensitivity when:

A

need to detect all diseased or infected animals

46
Q

maximize specificity when:

A

cost of false positive is high and dont care if there are lot of false negatives

ex: need to cull positive animals

47
Q

how to use Sp and Se in series

A

1st test: high Se

  • detects most/ all of diseased animals in population
  • negatives are true negatives

2nd test: high Sp

  • test all that tested positive on the first test
  • all test positives from second test are true positives (eliminates false positives from the first test)
48
Q

T/F Se and Sp tell you the probability that an animals which tests positive is truly diseased

A

false

tells you the probability of a diseased animal testing positive or non-diseased testing negative

49
Q

PPV

A

positive predictive value

true positive/test positives

50
Q

NPV

A

negative predictive value

true negative/test negatives

51
Q

how to calculate Se

A

true positives/ (true positives = false neagtives)

52
Q

how to calculate Sp

A

true negatives/ (true negatives + false positives)

RUSVM Epidemiology (18 decks)

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