9) Population Based Screening Flashcards
What are the different way in which disease can be detected?
Spontaneous presentation
Opportunistic case finding
Screening
What is the purpose of screening?
Give a better outcome compared with finding something in usual way, due to intervening earlier
What is screening?
Systematic attempt to detect an unrecognised condition by tests, examination and/or other procedures
What is a diagnosis?
Identification of a suspected disease through tests, examination and/or other procedures
What are the criteria that need to be considered for a screening programme?
Condition Test Intervention Programme Implementation
In terms of the condition, what things need to be considered if there is to be a new screening programme?
Important health problem that is well understood
All cost effective primary prevention intervention implemented
In terms of the test, what things need to be considered if there is to be a new screening programme?
Simple, safe, precise and validated
Cut off levels defined, test values in pop. known
Acceptable
Agreed policy on further diagnostic investigation to those that test positive
In terms of the intervention provided, what things need to be considered if there is to be a new screening programme?
Evidence that intervention at pre-symptomatic phase leads to better outcomes
Agreed policies on which people and what intervention should be offered
In terms of the programme itself, what things need to be considered if there is to be a new screening programme?
Effectiveness in reducing mortality
Clinically, socially and ethically acceptable
Benefit gained should outweigh harms
In terms of the implementation, what things need to be considered if there is to be a new screening programme?
Patient outcomes optimised
All other options for managing condition considered
Informed choice to potential participants
Quality assurance
What is a false positive in screening?
Refer well people for further investigation
What are the implications of false positives?
Stress, inconvenience and costs
Lower uptake of screening In future
What is a false negative in screening?
Failure to refer those who have an early form of disease
What are the implications of false negatives?
Inappropriate reassurance and delayed presentation
What is sensitivity?
Detection rate, proportion of people with the disease that test positive (a/a+c)
What is specificity?
Proportion of people who don’t have the disease who are correctly identified by the test as not having the disease (d/b+d)
What is the positive predictive value?
Probability that someone who is tested positive actually has the disease (a/a+b)
What is the negative predictive value?
Proportion of people who are test negative who actually don’t have the disease (d/c+d)
Why is evaluation required on screening programmes?
Programmes must be base on good quality evidence
Great pressure to start screening programmes
What is lead time bias?
Screened patients appear to survive longer but only because they were diagnosed earlier
What is length time bias?
Programmes better at picking up slow growing cases rather than aggressive, fast-growing ones, so screened diseases have favourable prognosis
What is selection bias, in reference to screening?
‘Healthy volunteer’ effect - those who are regularly screened likely to do other things that protect them from disease
Give some sociological critiques of screening:
Victim blaming
Population increasingly subject to surveillance
Moral obligation
Financial incentives for GPs to put patient in for screening
