Screening Flashcards
What is screening?
The process of identifying asymptomatic people and testing to identify if they are at an increased risk of a health condition so that preventative action can be taken.
What are the two different types of screening programmes in the UK?
Population screening
Targeted screening
What is population screening?
Universal or mass screening - entire pop or broad section, typically based on demographics (age or gender)
Aims to identify individuals with a particular conditions or risk factor within a general population even is asymptomatic
Reduce burden of disease and prevent its spread.
LArge group low risk
What is a targeted screening programe?
Nationally deliver proactive program - aims to improve health outcomes in people among groups at an elevated risk of a specific condition
Compared to general population targeted group has further risk factors e.g genetic or lifestyle
Inclusion criteria goes beyond age or sex
For example people who smoke regardless of age or sex.
Small group, high risk
What is the high risk approach of disease prevention in screening?
Target wise approach - reduce the risk of a high risk group down to the normal baseline
Focuses on a small population, typically used for rare diseases.
What is the population wide approach in disease prevention in screening?
Aim to reduce everyones risk (often equally) for a conditions
Graph shift left.
Focuses on larger population
What are the key principles of a screening test?
Offered to large number of people - tend to be simple rather than accurate
Look for indicators of an increased risk of disease
If increased risk often requires additional tests to confirm presence or absence of disease/condition
Screening tests cannot diagnose
What are the main aims of a screening programme?
Prevent - early deaths, poor quality of life by allowing early diagnosis and treatment
Reach - everyone in the population
Reduce - chance of developing a serious condition and complications
Provide - information for people to make informed choices about screening and further interventions
What different screening systems exist in NHS England?
Abdominal aortic aneurysm
Bowel cancer screening
Cervical screening
Diabetic eye screening
Newborn screening - NIPE
Screening in pregnancy - (fetal anomlay, infection disease)
What is the generic screening pathway?
Identify people to invite
Discuss and offer screening - if opt again, ask again, if opt out again return to routine invitation
Carry out screening test
Provide and discuss results/options
Carry out diagnostic/confirmatory test if required
Provide and discuss results/options
Offer advice/treatment
What is the purpose of UK NSC recommendations?
List summarise whether population screening is currently recommended for a condition or not and if open to public.
Reviews recommendation regularly, usually every 3 years, suggests who, when and what screening should be offered.
Describes best practice for national screening programmes.
What are the key benefits of screening programmes?
Reduce morbidity, mortality and disabilisty - better future health
(note unable to protect from exposure to disease)
More effective treatment
Reassurance
Informed decision (aka reproductive choice in antenatal screening)
Better use of resources
What are the key drawbacks of public health screening?
Not perfect: false negative or false positives leading to anxiety or false reassurance
Physical harm
Psychological harm
Financial harm
Overdiagnosis
What is over diagnosis as a concept in public health screening?
When screening test identifies person at increased risk - leads to increased diagnosis and treatment
However, no effect on morality rate
Suggests these new cases identified would not have had a harmful effect on health, no benefit from diagnosis/treatment.
Diagnosis of a condition that wouldn’t have caused harm in a person’s life.
What is the role of epidemioogy in screening?
Decide if disease has a natural history that makes screening an option
Disease burden significant enough
Test quality and estimate how ti might perform in the population
Assess potential of a screening programme to improve outcomes
Evaluate the performance of a screening programme in practice
What is the role of health economics in screening?
Is it cost-effective?
Completes cost-effectiveness analysis through measuring costs (Direct, indirect, long term health care)
Measuring benefits (health gains)
Incremental cost-effectiveness ratio (ICER)
How does public health screening contribute to health inequalities?
Barriers can result in some people being unable to access or complete screening.
People with greatest need are less likely to engage and benefit from screening increasing health disparities
This can increase inequaltities
At what point of the screening process can inequalities occur?
Cohort identification (invite)
Providing info about screening
Access to services
Access to treatment and onward referral
Outcomes
What are some macro barriers/indequaltities to engagement in public health screening?
These tend to be physical/institusion
Accessibility
HCP recommediation
Gender concordant HCP
Communication with HCP
What are some meso barriers to engagement in public health screening?
These are opportunity (social/cultural based)
Stigma and sexual connotation
Fatalism
Cancer is punishment from God
Acculturation
Role of the woman-putting family first
Lack of support from male/extended family members
What are some micro barriers to public health screening?
Participant/individual influences
Motivation - fear of outcome/procedure, low risk, self-efficact, perceived discrimination in healthcare
Capability - knowledge, difficult to make an appointment, health literacy, lack of time, having to do bowel screening oneself.
What are the requirements of a screening program relating to the disease?
Is the disease important health problem? Consider frequency and severity
is the natural history and epidemiology well understood?
Is there a long time between the presence of risk factors/sub-clinical disease or overt disease?
Are these risk factors highly correlated to the occurrence of disease?
Does early intervention improve clinical/public health outcomes?
Is the disease treatable?
If a genetic mutation related to condition is identified this should be explored in full?
What are the requirements of a screening program relating to the screening programme itself?
Is it simple, safe, precise and validated?
Is the cut-off defined and agreed?
Is the test acceptable to the target population?
Is there an evidence based for what populations should be invited?
If not treatable and focus is simply to make informed decisions (aka downs syndrome in pregnancy) should have high accuracy)
Benefits should outweigh harms to the individual
Should be economically and ethically acceptable and affordable for health care and the general public.
Should be a recognised quality assurance process?
Should be no other more cost effective alternative?
What are the requirements of a screening program relating to the treatment?
Is the disease treatable?
Has all other primary prevention interventions been implemented as far as possible?
Is there a clear plan on what to do if the test comes back positive does this improve outcomes compared to waiting for a symptomatic patient to present?
What is meant by true/false positives/negatives?
True - the result is what it says it is
False - result is not what it says it is.
Aka false positive - result is actually negative
What is meant by sensitivity of a screening programme?
True positive rate or recall - measure the ability of a test to correctly identify individual who have the disease.
High sensitivity indicates low false negative rate as rarely missed people who actually have the disease
How do you calculate sensitivity of a screening test?
True positives + False negatives
What is meant by the specificity of a screening test?
Measures the ability of a test to correctly identify individual without the disease (true negatives)
Is able to confirm the absence of a disease - low false positive rate (rarely gives a positive result if the disease is not present)
How do you calculate the specificity of a screening test?
True negatives + False positives.
What is meant by the predictive value of a screening test?
The probability of having the disease, given the result of a test.
AKa positive predictive value - probability of actually having the disease when having a positive test result
negative predictive value - prob of being negative when having a negative test result.
What factors influence the predictive value of a test?
Determined by sensitivity and specificity of the test
And the prevalence of disease in the population being tested.
Define prevalence in relation to disease
The proportion of persons in a defined population at a given point in time with the condition in question.
Increasing the sensitivity with increase the XXXXX positive predictive value
negative
Increasing the specificity will increase the xxxxx predictive value
Positive
How is the positive predictive value affected by the prevalence of the disease?
How can this be compensated for?
Lower preclinical disease prevalence = lower positive predictive value
To increase prevalence by reducing the population screening test is offered to.
How to calculate the positive predictive value?
true positives + false positives
How to calculate the negative predictive values of a screening test?
true negatives + false negatives
How do you calculate an ICER?
change in outcomes
What is the main goal of screening for a AAA?
Offered to all men the year they turn 65, offered an ultrasound to look for AAA.
If a large AAA is found may be offered surgery, if a small AAA is found may be offered repeat scans to monitor it.
Aim is to prevent rupture
Most AAA are asymptomatic before rupture
After 65yrs men may request an ultrasound scan to check but are not invited for one.
Suggest how prevalence can affect the positive predictive value, negative predictive value, sensitivity and specificity of a test.
Prevalence has no affect on sensitivty and specificity
Increase prev - inc PPV
Increase prev - dec NPP
