Session 6 - Screening Flashcards
Define screening
Screening is a systematic attempt to diagnose a previously unrecognised condition by the application of tests, examinations or other methods in a rapid, cheap way in order to distinguish between people who have the disease (or its precursor) and those who do not.
Give three different methods of detection of disease`
Spontaneous presentation
Opportunistic case finding
Screening
Outline the path of a positive screen result
Screen -> Positive screen -> Diagnostic tests -> Disease/no disease
Give four overall criteria which must be fulfilled before screening implemented
Disease
The test
Treatment
Programme
Give four points concerning disease which must be fulfilled before screening
Must be an important health problem
Epidemiology and natural history must be well understood
Must have an early detectable stage
Cost-effective primary interventions must have been considered and implemented
Give 6 points concerning the test which must be implemented before screening
Simple and safe Valid and precise Acceptable to the population Distribution of test values must be know Agreed cut off level for positive Agreed policy on who to follow up further
Give three treatments criteria
Effective evidence based treatment must be available
Early treatment must be advantageous
Agreed policy on whom to treat
Give three programme criteria
Other options considered
Benefit shoudl outweigh physical/psychological harm
Facilities for diagnosis and treatment
What is a false positive
Screening programme refers well people for further investigation
Offered diagnostic testig for a condition they do not actually have
What is a false negative
Failure to refer people who do actually have disease
False reassurance for patients
What is sensitivity?
Draw out table
Proportion of people with disease who test positive
a/a+c
What is specificity?
The proportion of people without the disease who are test negative
d/b+d
What is PPV?
Positive predictive value
The probability that someone who has tested positive actually has the disease
a/a+b
What is a stong influencer of PPV?
Prevalence of disease
“If I test positive, does that mean I definitely have the disease?”
Can two tests have different PPV and same sens and spec?
Yes
What is negative predictive value?
Proportion of peoplee who are test negative who actually do not have the disease
d/c+d
Give two advantages of screening
Early detection of disease may improve outcome
Reassurance for those who test negative
Give four disadvantages of screening
False positive - Uneccesary tests
False negatives - False reassurance
False negative - Not offered dianositc testing they may benefit from
Expensive intervention that divert money from testing
What is lead time bias?
o Screened patients appear to survive longer, but only because they were diagnosed earlier
What is length time bias
o Screening programmes are better at picking up slow-growing, unthreatening cases than aggressive, fast-growing ones
o Diseases that are detectable through screening are more likely to have favourable prognosis, and may indeed never have caused a problem
Curing people that don’t need curing?
What is selection bnias?
o Those who have regular screening are also likely to engage in other health behaviours that protect them from disease
o Similar to ‘healthy worker’ bias
o A RCT would help deal with this bias
Give three criticisms of screening programmes
Alteration of usual doctor-patient contract
Complexity of screening programmes
Limitations of screening (harm caused)
Give four examples of screening in UK
o Abdominal Aortic Aneurysm o Bowel cancer o Breast cancer o Cervical cancer o Diabetic Retinopathy o Down’s syndrome o Foetal anomalies o PKU o Sickle Cell and Thalassaemia
Give four categories of sociological critiques for screening
Structural critiques
Surveillance critiques
Social constructionist
Feminist critique
Give two structural critiques
o Victim blaming
Individuals encouraged to take responsibility for their own health
Are all equally able to do this?
o Individualising pathology
What about addressing underlying material causes of disease?
Give a surveillance critique
o Individuals and populations increasingly subject to surveillance
o Prevention part of wider apparatus of social control?
Give a social constructionist critique
o Health and illness practices can be seen as moral – given meaning through particular social relationships
Give a feminist critique
Is screening targeted more at women?
