Population Screening

Question 1

What is screening?

Answer 1

-Process of identifying healthy people at higher risk of a health problem
-Test apparently healthy individuals before onset of symptoms

(if get +ve result - those people progress on for further testing)

IMPORTANT -> those who get -ve result once can go on to develop condition in future!

Question 2

Aims of screening?

Answer 2

-Reduce risk of future ill health by early treatment
-Give info for informed decision making

Question 3

What is population screening?

Answer 3

Test target group in structured programme

Question 4

What type of screening, is population screening an example of?

Answer 4

Secondary prevention strategy

Question 5

Define:
-Primary prevention strategy
-Secondary prevention strategy
-Tertiary prevention strategy

Answer 5

-Primary = stop disease process before starts - e.g., vaccination, smoking cessation
-Secondary = find ‘things’ (symptoms) early so can do something about them - i.e., reduce impact of disease progression - screening for early detection & treatment, prescribing statins to lower cholesterol
-Tertiary = stop a disease - e.g., heart attack, stroke - from happening again in future - so soften impact of ongoing illness -> e.g., via cardiac rehab

Question 6

What does a normal/screen negative result mean?

Answer 6

LOW RISK
-Doesn’t mean won’t get the disease in future
-Doesn’t mean should ignore symptoms suggestive of the disease
-Continue with normal screening interval

Question 7

What does screen positive mean?

Answer 7

HIGHER RISK
-Further info/investigation recommended
-NB can stop here – patient choice (autonomy)

Question 8

What conditions do we (NHS - NSC UK) choose to screen for -> population screening & who is the target group & what is the test?

Answer 8

Cervical cancer - do HPV 1st then if this is +ve (i.e., have found HPV) then give cytology test (= a triage to check for any abnormal cells)

Question 9

What are some genetic screening tests offered in NHS?

Answer 9

-Sickle cell disease
-Thalassaemia
-Cystic fibrosis
-PKU = Phenylketonuria

Antenatal & newborn screening involve testing for these genetic disorders - but also chromosomal disorders

Question 10

What is done for transgender & non-binary individuals with regard to screening?

Answer 10

-Automatic invitation - gender are registered as with their GP influences screening invited for
-Risk depends on individual circumstances
-Individuals can request screening if not offered – e.g., if have cervix but registered male
-Need to be aware of symptoms & able to access medical attention if required
-Can be emotive & needs should be handled sensitively – e.g., offer appts at beginning/end of day

Question 11

What are some non-NSC programme (i.e., not actual screening by NSC definition)?

Answer 11

-NHS Health checks
-National Child Measurement Programme
-National Chlamydia Screening Programme
-Chest x-ray screening for TB
-Other types of genetic testing
-Important ethical considerations

Question 12

Population screening timeline?

Answer 12

11 population screening programmes available in England

Question 13

When are the 3 types of screening programmes in UK?

Answer 13

-Antenatal
-Newborn
-Adult

Question 14

What is the UK NSC?

Answer 14

-Makes recommendations based on evidence including economics
-Benefits & risks
-Reviews recommendations every 3 years
-Provides recommendations on 109 conditions

Question 15

What are the 4 pieces of criteria for a screening programme?

Answer 15

*Condition
-> a condition must be: important, well understood, have a latent period (a time before symptoms start), primary prevention (which must 1st be exhausted)
*Test
-> tests involved in screening must be: simple, safe, validated, acceptable, non-invasive
*Intervention
-> should have effective treatment following +ve screening test (available treatment)
*Screening programme
-> evidence-based, benefits outweigh harm, cost-effective, properly resourced

==> if not then screening is not beneficial (-ves outweigh +ves)

Question 16

Summarise criteria for a screening test.

Answer 16

-Safe
-Reliable
-Non-invasive (stool samples & smear = non-inv - BUT uncomfortable for people -> so good communication = crucial!)
-Cheap
-Acceptable

Question 17

Define sensitivity in terms of screening.

Answer 17

= probability of +ve result if disease is truly present (so -> if actually have the disease - it is the probability the test will show this - as +ve result)
-Measure of how good test is at identifying +ve cases
-High sensitivity results in few false -ves

Question 18

Define specificity in terms of screening.

Answer 18

= probability of testing -ve if disease is truly absent (-> so if actually don’t have the disease - it’s the probability the test will show this - as -ve result)
-Measure of how good test is at correctly ruling out those without the disease
-High specificity results in few false +ves

Question 19

Define false -ve?

Answer 19

-ve result but truly have the disease

Question 20

Define false +ve?

Answer 20

+ve result but do not have the disease

Question 21

Is screening high in sensitivity or specificity?

Answer 21

Screening tests often have high sensitivity - may result in lots of false +ves – acceptable if screening test is not harmful or expensive

Question 22

Are diagnostic tests high in sensitivity or specificity?

Answer 22

Diagnostic tests – high specificity – importance of diagnostic precision

Question 23

Define positive predictive value (PPV).

Answer 23

= probability of truly having the disease with a +ve test (-> so get +ve result - so you really have it? - this is a measure of this!)
-Proportion of those who have +ve test who truly have the disease

Question 24

Define negative predicative value (NPV).

Answer 24

= probability of truly having the disease with a -ve test (-> so get -ve result - so do you really not have the disease? - this is a measure of this!)
-Proportion of those who have +ve test who truly have the disease

Question 25

How to say whether someone has a:
-Sensitivity
-Specificity
-PPV
-NPV

Answer 25

= 2 by 2 table!!!

Question 26

What influences sensitivity & specificity?

Answer 26

No test =100% sensitive & specific
-Level of sensitivity & specificity is acceptable depends on circumstance e.g., how invasive next step in screening programme is
–> accept less false +ves if treatment very aggressive

Question 27

Give 3 types of biases in screening.

Answer 27

-Selection bias
-Lead time bias
-Length time bias

Question 28

Define selection bias.

Answer 28

-Healthy “screenee” effect
-People who attend screening in general are lower risk & healthier than those who don’t

Question 29

Define lead time bias.

Answer 29

Screening identifies people with a disease earlier - so looks like have survived longer than those diagnosed without screening

Question 30

Define length time bias.

Answer 30

Screening more likely to pick up slower growing disease than faster more aggressive disease - because is more time to detect it - so people identified through screening appear to have better prognoses

Question 31

Outline the 4 pillars of medical ethics.

Answer 31

-Beneficence (doing good)
-Non-maleficence (to do no harm)
-Autonomy (giving patient freedom to choose freely, where they are able)
-Justice (ensuring fairness)

Question 32

Give some considerations regarding beneficence in screening.

Answer 32

-Population vs individual benefit
-Can identify conditions early & can lead to better outcomes
-Most participants will not individually benefit e.g., would not have gone on to get that cancer anyway
-Very helpful on population wide basis

Question 33

Give some considerations regarding non-maleficence in screening.

Answer 33

-Potential harm
-False +ves
–> psychological harm due to anxiety, iatrogenic harm from often invasive subsequent tests or unnecessary treatment
-False -ves
–> false reassurance & potentially ignore symptoms
-Overdiagnosis (may not have otherwise become apparent in person’s lifetime)
-Difficult decisions may need to be made e.g., antenatal screening

Question 34

Give some considerations regarding autonomy in screening.

Answer 34

*Informed consent
-Need information leaflets in accessible language & other languages
-Videos
–> HEALTH LITERACY - some people may find info given too complex to understand - & do not assume everyone can read
-Opportunities to ask questions
*Communicating risk is really difficult
-Unclear if majority of people who take part actually understand potential consequences
*Importance of patient choice
-Target uptake is not 100%

Question 35

Give some considerations regarding justice in screening.

Answer 35

-National screening programme should not widen inequalities!!!
-Those who could benefit most, often less likely to access screening
-Need to understand potential barriers
-3 C Model of Vaccine Hesitancy useful: Convenience, Complacency, Confidence
-Lower uptake seen in more deprived areas; ethnic minority backgrounds; men; LGBTQI+ communities; those experiencing homelessness & members of travelling community (need to be registered with GP to get most screening invitations)

SO -> WHAT ARE PEOPLE’S BARRIERS TO ACCESSING SCREENING?

Question 36

Apply 3 C model to justice in screening.

Answer 36

-Convenience –> accessibility in terms of timing/location (public transport, childcare)
-Complacency –> do not feel it is needed – importance of good info & understanding risks
-Confidence –> lack of confidence in healthcare services or process

Question 37

Benefits & risks in screening?

Answer 37

Opportunity cost -> loss of benefit from next best course of action, once a decision has been made
–> money & resources used for screening cannot be used elsewhere