Diagnostics tests

Question 1

Diagnosis

Answer 1

CLASSIFY animals as having disease or not

Question 2

2 types of Diagnostic tests results

Answer 2

Dichotomous = 2 possible answer (- or +)

Continuous = continuum of possible answers

Question 3

Hematology Diagnostic test measure

Answer 3

amount of different cell types in venous blood sample

          CBC, Differential blood count, PCV

Question 4

Biochemical Diagnostic test measure

Answer 4

enzymes, metabolites, proteins in venous blood

       liver enzymes, BUN, CREA, amylase, lipase

Question 5

Immunological Diagnostic test measure

Answer 5

antibodies (ELISA, IFA, Western blot, SNAP FIV/ E.cani)

use antibodies to detect antigen
SNAP FeLV / heartworm

Question 6

FIV/FeLV snap tests detect

Answer 6

anti-FIV antibodies or FeLV antigens

Question 7

Pathogen detection test

Answer 7

Detect pathogens itself (not antibodies against it)
present during infection with no time Lag

PCR detecting pathogen DNA/ RNA in clinical sample

Question 8

How is decision of test made?

Answer 8

Cut off value is used which was determined experimentally as the test value that minimizes False +/ -

Question 9

How to determine if test value is + / -

Answer 9

test a lot of individuals
proven to have disease or condition
proven to not have disease or condition

Define cut-off that best separates the two tested groups

Question 10

False Positives

Answer 10

Non-disease animals that test positive (Sp issue)

Question 11

False Negatives

Answer 11

Diseased animals that test negative (Se issue)

Question 12

2 parameters of evaluating Diagnostic tests/

Answer 12

Sensitivity (Se) and Specificity (Sp)

Question 13

Sensitivity (Se)

Answer 13

proportion of diseased animals that correctly test positive

Question 14

Specificity (Sp)

Answer 14

Proportion of non-diseased animals that correctly test negative

Question 15

Low specificity causes

Answer 15

contamination
mistake pathogen ID
animals with antibodies from vaccine (not infection)

Question 16

SnOUT

Answer 16

highly sensitive test rules disease OUT
(NO false negatives)

    negative result from highly sensitive test is most likely 
                        from non-diseased animal 
                          (RULES OUT DZ)

false positive are possible if Sp is low

Question 17

T/F: Sensitivity tells you about how well the test performs on Non-diseases animals

Answer 17

False:

Doesn’t tell you a fucking thing about non-diseased

Question 18

Another way of saying Specificity

Answer 18

how often the test detects the things specifically intended to detect - Not healthy animals

Question 19

SpIN

Answer 19

highly specific test rules Disease IN

most positive results are from diseased

Question 20

75% Sp

Answer 20

correctly classifies 75% non diseased animals as negative

25% non diseased as positive (false positives)

Question 21

100% Sp

Answer 21

correctly classifies all non-diseased animals as negative
(if Se low than false negatives possible)

doesn’t tell you how well test performs on diseased animals

Question 22

What do you never want as test results?

Answer 22

False negatives

Question 23

How to test imported animals for infections?

Answer 23

test with High Se and only allow negative results to enter country

Question 24

maximize sensitivity when?

Answer 24

you need to detect ALL disease or infected animals

Question 25

maximize Specificity when?

Answer 25

testing for very serious diseases with serious consequences

Question 26

High Sp

Answer 26

correctly classify ALL non-diseased animals as negative

Question 27

To accuratly detect all diseased and eliminate non diseased animals?

Answer 27

1st : high Se 2nd: high Sp

Question 28

T/F: Se and Sp doesn't tell you the probability of + is truly disease PPV and NPV do this

Answer 28

True

Question 29

PPV

Answer 29

Positive predictive Value answers my patient tested positive and probability it has disease only include true positives and false positives

Question 30

NPV

Answer 30

Negative predictive value answers my patient tested negative and probability it doesn't have disease true negatives and false negatives

Question 31

Se and Sp won't change if prevalence of disease in population changes

Answer 31

True

Question 32

PPV and NPV will change as prevalence of disease in population changes

Answer 32

True