interpretation of diagnostic results

Question 1

what factors allow us to use lab tests to define definitive diagnosis

Answer 1

• reference intervals (what we expect to see in a normal animal)
• interpretive thresholds (diagnostic cutoffs as defined in literature)
• positives/negatives (infectious diseases etc)

Question 2

define sensistivity

Answer 2

the proportion of animals with the disease that yield a positive result (true positives)
- indicates the ability of a test to correctly identify individuals with a disease)
- a test with high sensitivity will inimise false negatives and therefore make if a good screening test

Question 3

what is specificity

Answer 3

the proportion of animals that dont have the disease that yield a negative test result (true negatives)
- indicates the ability of the test to identify individuals without a disease
- a test with high specificity will minimize the false positives and therefore make a good confirmatory test

Question 4

when would you want to use a screening test vs a confirmatory test

q

Answer 4

screening: for cases where the disease that you are suspicious of you wouldnt want to miss (catching false positives is ok but false negatives are bad)
confirmatory: when you want to be absolutely sure that the animal has the suspected disease (minimal false positives)

Question 5

what are consequences of bad sensitivity tests

Answer 5

• diagnosis missed (-ve result in diseased animal)
• may re-present or be referred
• outbreak may worsen in epidemic
• costs (financial, life, welfare, emotional)

Question 6

what are consequences of bad specificity tests

Answer 6

• diagnosis when disease is absent
• unnecessary life long therapy (especially in endocrine diseases)
• unnecessary euthanasia
• costs (finanacial, life, welfare, emotional)

Question 7

what is prevalence

Answer 7

• the proportion of animals in the tested population that have the condition
• aka pre test probability (the likelihood the animal has the disease before any tests are done)
• only testing animals for a disease that have several relevent clinical circumstances results in high pre test probability
• testing a widespread healthy population to screen for infectious disease results in low pre-test probability

Question 8

if you have a positive result, how do you know if you can trust it

Answer 8

• PPV will tell you if you can trust the test (makes sense that the animal is positive)
• apart from prevanence, rely on specificity
• low specificty tests have poor PPV except when prevenalce is high
• high specificity test have good PPV even at low prevalence

Question 9

in the case of a negative result, what values can inform you of how trustworthy the test result is

Answer 9

• NPV (proportion of negative results in population)
• or sensitivity

Question 10

how can we mitigate the challenges of getting accurate and precisise test results in endocrinopathy related diseases

Answer 10

• look at how the hormone responds when chellenging it to do something
• does it respond abnormally or normally.
• stimulate it to priduce more hormone
• supress it using the principle of negative feedback)
• monitor blood concentrations to see if they change on pathological levels

Question 11

how do you calculate PPV, NPV, prevalence, sensitivity, specificty and accuracy

Answer 11

Question 12

what is positive predictive value

Answer 12

the proportion of animals with a positive test that really have the disease

Question 13

what is negative predicive value

Answer 13

the proportion of animals with a negative result that reallydo not have the disease