S8 - Screening Flashcards
What is the purpose of screening
- Identifying ‘healthy’ people who may have increased chance of developing a disease or condition
- Prevent earlier deaths/improve QoL by detecting a condition at a stage where treatment is more effective
- Reach everyone in target population
- Reduce the chance of people developing a serious condition
What are the three types of screening programmes
Population
☞ individuals are actively invited for screening
☞ offered to a group of people identified from the whole population
☞ eg by demographics, age, sex
targeted
☞ groups of people identified as being above risk of a specific condition
☞ eg by lifestyle factors, genetic variants or co-morbidity
stratified
☞ offering testing that varies in frequency and modality (varying types of test offered)
☞ this is done according to individual risk
☞ stratification is used in population + targeted screening too
☞ eg people with increased risk of breast cancer can be screened more often depending on their level of risk
Give some examples of UK population-based screening programmes
- Diabetic eye
- Bowel cancer
- Breast cancer
- Fetal anomaly
- Infectious diseases in pregnancy
- Newborn hearing programme
- Sickle cell and thalassaemia
- Newborn blood spot
- Newborn and infant physical examination
- Cervical cancer (above 25 y/o)
Criteria for screening
- condition importance of health problem
- test simple, safe, precise and validated? Acceptable to target population? Αgreed policy on further diagnostic investigation?
- intervention effective for patients identified through screening? Evidence based policies setting out which individuals should be offered interventions
- screening programme proven effectiveness in reducing morbidity and mortality? Is programme clinically, socially and ethically acceptable to public + HCPs? Benefit outweigh harms?
- implementation patient outcomes should be optimised. Quality assurance (management + monitoring), adequate staffing, evidence-cased info available to participants (so they can make informed choice)
Pros and cons of screening
pros
- Reduce incidence of disease and/or mortality
- Reduce chance of developing condition or complications
- Earlier detection facilitates better treatment outcomes
- Early stage treatment can save money
disadvantages
- False positive
- False negative
- Overdiagnosis
Barriers of screening
- Forgetting
- Lack of information (and therefore informed choice)
- Access to screening eg booking
- Communication eg different languages
- Physical mobility
- Financial barriers
Why is informed choice in screening important + the principles
- people can respond differently when faced with the same information about the potential benefits and risk
- decision made based on access to accessible, accurate, evidence-based information covering…
☞ the conditions being screened for
☞ the testing process
☞ risks, limitations and benefits etc
☞ potential outcomes and the decisions afterwards
Screening is a form of…
Secondary prevention (Secondary prevention aims to reduce the impact of a disease or injury that has already occurred)
What is the definition of diagnosis
The definitive identification of a suspected disease or defect by application of tests, exams or other procedures to definitely label people as either having a disease or not having a disease
any screening programme is going to make two main errors
going to refer well people for further investigation
- false positive
- stress + anxiety
- direct costs
- opportunity costs
**going to fail to refer people who do actually have an early form of the disease
- false negative
- inappropriate reassurance
- possibly delay presentation with symptoms
The features of test validity (details on separate cards)
- sensitivity
- specificity
- positive predictive value (PPV)
- negative predictive value (NPV)
Features of test validity: sensitivity
- the proportion of the people with the disease who test positive
- aka detection rate
- the proportion of the people who really have the disease who are identified correctly as having the disease
Features of test validity: specificity
- the proportion of people without the disease that test negative
- the proportion of the people who really do not have the disease who are identified correctly by the test as not having the disease
Features of test validity: positive predictive value (PPV)
- ‘if I test positive, do I have the disease’
- The probability that someone who has tested positive actually has the disease
- This value is strongly influenced by the prevalence of the disease
features of test validity: negative predictive value (NPP)
- The proportion of people who test negative that actually do not have the disease
- ‘if the screening test is negative, what are the chances that I really don’t have the disease?’
