The principles of population Screening Flashcards
What is screening?
The process of identifying healthy people who are at a higher risk of developing a health problem.
Then testing these indivduals before the onset of symptoms
What is the purpose of screening?
Reduce the risk of future ill health via early treatment
To give information for informed decision making
What is meant by population screening?
Tests a target group in a structured programme.
What type of prevention stratgery is screening?
Secondary
Note primary - stops a disease before it happens
Secondary - identify a disease in an early stage
tertiray - when an event is already happened, prevent it from getting worse or happening again
What is the meaning of a positive or negative screening result?
Positive - increased risk of a disease developing
Negative - decreased risk of a disease developing
*specific to a time and circumstance, results may change at a different date.
What are some of the options after a positive screening test result?
Advice and support
Treatment for condition to slow progression
No further action (if further tests are negative)
Further tests - always happens first regardless of the above options.
What do we need to ensure patients with a negative screening test result understand?
Low risk at this moment of time in these conditions
May still get the disease in the future
Should still check out any unusual symptoms at the doctors
Should return for next screening interval as normal
What do we need to ensure patients with a positive screening test result understand?
Further information and investigations are often needed/recommended
The patient can refuse further tests
This indicates they are at an increased risk having a disease, this is not always a diagnosis with this disease.
What are the different criteria for a screening programme?
Condition - important (effect quality/qunatity of life), well understand, longer latent period, primary prevention or treatment available
Test - simple, safe, acceptable
Intervention - effective
Screening programme - evidence based, benefits outweight costs, properly resourced
What is meant by a latency period and why is it important in public health screening?
Latency period is the time between when a disease is identifiable and when the symptoms start
Diseases with a longer latency period are more likely to be picked up in and benefit from early treatment from a screening test.
How should a test be designed to be acceptable?
Non-invasive (not needing to cut into anyone)
Low ‘eew factor’ patients are often less willing to do a stool sample for example
Patient comfort
Social stigma
e.g around cervical smeer test.
What does sensitivity mean in regards to a screening test?
The probability of testing positive if the disease is truly present
Should have few false negatives
What does specificity mean regarding a screening test?
Probability of testing negative if the disease is truly negative.
Should have few false positives
What is positive predictive value in regards to screening programmes?
PPV - probability of truly having the disease based on a positive test outcome.
What is negative predictive value in regards to public screening test?
The probability of truly being disease negative based on a negative test outcome.
What is important to remember when analysing PPV and NPV statistics?
Values are influenced by community background and time sensitive situations
E.g during peak pandemic when more people had COVID the PPV value was higher as you probably did have covid even without testing.
How do you calculate sensitivity of a screening programme?
True prositives + False negatives
How do you calculate specificity of a screening programme?
True negatives + False positives
How do you calculate the positive predictive value for a screenin test?
True positives + false positive
How do you calculate the negative predictive value for a screening test?
True negative + false negative
What are the different biases that need to be considered when designing a public screening programme?
Selection bias
Lead time bias
Length time bias
How might selection bias be present in a public health screening program?
People who attend screening are more likley to have a better attitude towards health, so will be healthier and less likley to have the disease anyway
How might lead time bias be present in a public screening programme?
Screening identifies people with a disease earlier, this can make it look like they have lived with the disease longer, whilst in reality they have just been diagnosed earlier than symptoms would normally prompt diagnosis
How might length time bias present itself in a public health screening program?
Screening is more likley to pick up slower progression diseases, these normally have a better prognosis anyway regardless of screening
How does the beneficence medical ethical pillar fit into public health screening?
Population v individual benefit - e.g lockdown
Does early detection lead to better outcomes
Most individuals do not benefit anyway, is this waste overwhelmed by the benefit to the minority who do screen positive
Benefit to nation wide health.
How does non-maleficence medical ethical pillar apply to public health screening?
False positives - psychological harm, itarogenic harm due to subsequent tests or treatment
False negatives - false reassurance
Overdiagnosis - may otherwise have not become apparent in a persons life.
Difficult decisions may need to be made based on results - e.g antenatal screening and abortion
What is meant by opportunity costs in relation to public health screening programmes?
Is the investment in screening worth it?
The money and resources used for screening can’t be used elsewhere, would other programmes have more benefits.
How does autonomy apply to public health screening?
Informed consent - including an opportunity to ask questions
Communicating risk is really difficult - patient needs to understand what the consequences of a positive or negative result may mean before taking the test
Patient choice - may refuse (normally why target uptakr is not 100% as this would imply people were being forced)
How does justice apply to public health screening?
Should not widen inequalities - either based on results or access
Those who would likley benefit the most are the least likley to attend a screening appointment
Need to understand and remove barriers (Covenience, complacency and confidence)
Uptake is wrongfully lower in certain communities - deprivation, ethnic minorities, homeless (require an address to register with a GP)
What is the UK National Screening Committee?
Make recommendations based on evidence (inlcuding economics) or how screenign programmes should change/stop/start
Benefit and risk analysis
Review screening programmes every 3 years
Currently provides recommendations on screening for 109 conditions.
Includes decisions of antenatal, newborn and adult screening programmes)
How does public health screening vary across the UK?
Each of the four nations makes their own decisions reagaring screening
Northern Island has an additional Farm Families Health Check Programme.
What are the current screening programmes on offer by the NHS in England?
Currently 11 programmes (current research on if lung cancer should be added)
AAA screening
Bowel Cancer Screening
Breast cancer screening
Cervical cancer screening
Diabetic eye screening
Newborn screening
Screening in pregnancy
What are the different NHS England pregnancy screening programmes that are offered?
FASP - foetal anomaly screening programme
IDPS - infectious diseases in pregnancy screening
NIPE - newborn and infant physical examination
NBS - Newborn blood spot screening
NHSP - newborn hearing
SCT - Newborn Sickle Cell and Thalessemia
What is the deal with abdominal aortic aneurysm screening programme?
For men aged 65yrs old
One off abdominal ultrasound
What is the deal with the bowel cancer screening programme?
People aged 60-74 years old
Stool sample in the post
FIT test (feocal immunochemical test) looks for blood in poo
Every 2 years
What is the deal with the breast cancer screening programme?
Women aged 50-71 yrs olf
Mammogram every 3 yeards
What is the deal with cervical cancer screening programme?
Women aged 25-64 yrs eold
Cervical smear, first looking to identift HPV vaccine then cytologoy looking for cell changes
Every 3 to 5 years depending on age
What is the deal with the diabetic retinopathy test?
In people with diabetes aged 12yrs+
Eye test
Yearly
What is the deal with antenatal screening?
Part of routine antenatal care
Includes Blood tests and ultrasound scanning, some tests are more invasive.
What is the deal with genetic screening programmes of newborns?
Testing for genetic and chromosomal abnormalities
Autosommal recessive disorders include: sickle cell anemai, cystic fibrosis, thalassaemia and PKU.
How should screening programme care be adapted for trans and non-binary people?
Ensure they are tested for conditions based on anatomical risk.
Emsure invitations are respecful of patient gender and explain why they still need to be done
May prefer an ealry or late appointment time to avoid uncomfortable environments
Need to be aware of symptoms and all tests available to them
Appointments often need to be handled more sensitivly
What is meant by quality measure in regards to public health screening?
The process of ensuring that national standards are met and encouraging continous improvement
Screening Quality Assurance Service Assessments
Have quality assurance visists
Ass aspects of screening should be tested and approved.
What are some non- NSC programmes that are still screening?
NHS health checks - 40 to 74yrs olf based on preexistning health consitions
National Child measurement programme - school height and weight checks in reception and year 6
National Chlamidya Screening Programme - online self referall form for 15 to 24yrs
Chest x-ray for TB
Other genetic testing
