PASS S8 - Screening Flashcards
What are the 5 areas of criteria?
Condition Test Intervention Screening programme Implementation
What does the condition mean in relation to screening criteria?
An important health problem with epidemiology, incidence, prevalence and natural history understood
What does the test mean in relation to screening criteria?
Simple, safe, precise and validated screening test
Distribution of test values in the population must be known and an agreed cut-off level must be defined and agreed
What does the intervention mean in relation to screening criteria?
Effective intervention for patients identified through screening, with evidence that intervention at a pre-symptomatic phase leads to a better outcome for the screened individual compared with usual care
What does the screening programme mean in relation to screening criteria?
Proven effectiveness in reducing mortality or morbidity
Benefit gained by individuals should outweigh any harms
What does implementation mean in relation to screening criteria?
Clinical management and patient outcomes should be optimised in all healthcare providers
All other options for managing the condition should have been considered
Quality assurance of the programme
What is lead time bias?
Early diagnosis falsely appears to prolong survival (screened patients appear to survive longer, but only because they were diagnosed earlier)
Patients live the same length of time, but longer knowing they have the disease
What is length time bias?
Screening programmes better at picking up slow growing unthreatening cases than aggressive, fast-growing ones
Curing people that don’t need curing
What is selection bias?
Studies of screening often skewed by ‘healthy volunteer’ effect
Those who have regular screening likely to also do other things that protect them from disease
An RCT would help deal with this bias
Which type of prevention is screening?
Secondary
What are the two types of error in screening tests?
False positives
False negatives
What is the sensitivity of a test?
The proportion of the people with the disease who test positive
High sensitivity = good at picking up the disease
What is the specificity of a test?
The proportion of the people without the disease who test negative
High specificity = good at ruling out people who don’t have the disease
What is the positive predictive value?
Probability that someone who has tested positive actually has the disease
What is the negative predictive value?
Proportion of people who test negative who actually do not have the disease
