Block 10

Question 1

Name some types of tests =

Answer 1

Biological - Hb, Ca2+, ALT
Images - CXR, mammogram, ultrasound
Questions - CAGE
Examination - tactile vocal fremitus

Question 2

Tests act to

Answer 2

Shift our understanding on the continuum

Question 3

A good test maximises what and minimises what

Answer 3

Maximises = true positive and true negatives
Minimises = false positives and false negatives

Question 4

True positive rate is the same as

Answer 4

Sensitivity

Question 5

True negative rate is the same as

Answer 5

Specificity

Question 6

Sensitivity definition =

Answer 6

Number of people with a positive test who actually have disease

Question 7

Specificity definition =

Answer 7

Number of people with negative test who truly don’t hace disease

Question 8

Sensitivity equation =

Answer 8

No of people with true +ve/all with disease

Question 9

Specificity equation =

Answer 9

No of people with true -ve/all people without the disease

Question 10

How can you summarise the impact of a test result?

Answer 10

PPV and NPV

Question 11

PPV definition =

Answer 11

The change of really having disease with a positive test result

Question 12

NPV definition =

Answer 12

The chance of really not having disease with a negative test result

Question 13

PPV equation =

Answer 13

No. of true positives/all those who tested +ve

Question 14

NPV equation =

Answer 14

No of true -ves/all those who tested -ve

Question 15

Unlike NPV and PPV, sensitivity and specificity remain

Answer 15

Constant

Question 16

What can change NPV and PPV?

Answer 16

Prevalence

Question 17

What changes the prevalence?

Answer 17

Primary vs secondary care
Age
Country

Question 18

Why are tests used differently in primary and secondary care?

Answer 18

DIfference in PPV and NPV

Question 19

When prevalence increases …

Answer 19

PPV increases

NPV decreases

Question 20

When prevalence decreases

Answer 20

PPV decreases

NPV increases

Question 21

What can tell you how tests are best used in clinical practice?

Answer 21

Likiehood ratio

Question 22

Each test has how many likelihood ratios?

Answer 22

2 - LR+, LR-

Question 23

LR+ =

Answer 23

Sensitivity/false +ve rate

Question 24

LR - =

Answer 24

Specificity/ false -ve rate

Question 25

Chances of disease after test =

Answer 25

Chances of disease before test x LR

Question 26

Screening =

Answer 26

Systematic appilation of a test to identify individuals at sufficient risk to warrent further investigation/prevention amongst persons who haven't sought medical attention on account of symptoms.

Question 27

Examples of screening

Answer 27

``` AAA Diabetic eye Blood spot Newborn hearing Newborn physical exam Fetal anomalies Breast, cervical, colorectal cancer ```

Question 28

Screening is what type of prevention?

Answer 28

Secondary

Question 29

When do we screen?

Answer 29

- More definitive tests are risky or unpleasant - Limited opportunity for primary prevention - Treatment limited - Early treatment associated with better outcomes

Question 30

Screening occurs in what phase of a disease?

Answer 30

Presymptomatic phase

Question 31

Criteria to decide what is screened for can be broken into what categories?

Answer 31

1. Disease 2. Test 3. Treatment 4. Program

Question 32

Screening: the condition must be

Answer 32

- Identifiable risk factor - Latent period - An important problem - Epidemiology and natural Hx well understood - All cost-effective primary prevention is exhausted

Question 33

Screening: the test must be

Answer 33

- Simple, safe, precise - Acceptable - Have an identifiable cut off - Agreed management following positive result

Question 34

Screening: the treatment must be

Answer 34

- Evidence that early treatment causes better outcomes - Agreed policies on who gets offered - Optimised before screening

Question 35

Screening: the program must be

Answer 35

- Acceptable - Benefits>risk - Cost effective - Opportunity cost - RCT evidence it reduces mortality and morbidity

Question 36

Opportunity cost =

Answer 36

The loss of other alternative when one alternative is chosen

Question 37

What needs to be done before a screening test is rolled out?

Answer 37

Clinical trial

Question 38

Selection bias in screening RCTs

Answer 38

Healthy people tend to uptake screening | Length bias

Question 39

What is length bias?

Answer 39

Screening tends to pick up slower progressing diseases and these diseases automatically have better prognosis

Question 40

How do we get around selection and length time bias

Answer 40

Intention to treat/intention to screen analysis

Question 41

What is the lead time?

Answer 41

Time between detection of a disease and clinically apparent symptoms

Question 42

What is lead time bias?

Answer 42

Those with disease picked up through screening have a longer lead time so have a longer survival from diagnosis

Question 43

How do we get around lead time bias?

Answer 43

Measuring deaths prevented rather than survival

Question 44

Test for colorectal cancer =

Answer 44

Faecal occult blood | Flexi-sig

Question 45

Test for prostate cancer =

Answer 45

Prostate specific antigen (PSA)

Question 46

PPV of FOB

Answer 46

2%

Question 47

PPV for PSA

Answer 47

30%

Question 48

Who benefits from screening

Answer 48

- Not false -ve - Not false +ve - True -ve somewhat - Some true +ves but not all

Question 49

What is the problem with prostate cancer screening?

Answer 49

Catch too many slow growers or non-progressors.

Question 50

What logic is at the heart of ethics?

Answer 50

Utilitarian

Question 51

Autonomy issues with screening:

Answer 51

Are people actually chosing, especially children and infants

Question 52

What is good about good screening?

Answer 52

Early detection can reduce risk of death or illness

Question 53

What is bad about good screening?

Answer 53

False +ves Over investigation and treatment Some people get true +ves but this doesn't prevent deaths