Screening Flashcards
Screening define, what is it not
actively identifying unrecognised disease or pre disease in apparently healthy subjects who are more likely to benefit from early treatment than be harmed
Misuse of term=testing, case finding, opportunistic screening are not screening
Expectation of screening
Undiagnosed condition could be identified at an early stage so that management of it can be started early on
Symptomatic new cases of a disease are the minority at any time and screening programme will uncover large new cases
Types of screening in UK
Cancer-breast, cervical, bowel
Cardio-abdominal aortic anuerysm, diabetic retinopathy
Antenatal and newborn
What makes screening worthwile
Condition: frequency and impact on individual, primary prevention ineffectiive, identifiable preclinical stage of disease
Test: there’s test separating those with high and low probability of disease
Treatment: effective treatment is available and outcome of early treatment is better
Characteristic of screening test
simple, safe, precise
clear distinction normal+abnormal results
acceptable to subjects, reasonable cost
agreed policy on further diagnostic investigation of individuals with positive result
What is lead time
Interval between diagnosis of disease at screening and usual time of diagnosis by symptoms
Biases associated with screening
Lead time (interval between the time of detection by screening and the time at which disease would have been diagnosed) Length-biased sampling (rapidly progressive disease makes individual more likely to consult) Selection bias (those who enter screening are more health conscious) Overdiagnosis bias (lesions identified as disease in screening programme would not have presented clinically during individual's life time
Solution for biases
RCT when mortality than survival is used as outcome. Survical only ussed if there is no evidence of overdiaagnosis bias and observation period is from randomisation date
Pros+cons of screening
Pro: improve prognosis for true positives, less radical treatment required, resource saving, reassurance for those with true negative
Cons: longer period of awareness for true positive whose prognosis is unaltered, over treatment for borderline abnormalities, false reassurance of false negatives, anxiety and hazard for false positives, hazard of screening test to all recipients
How is quality assurance done in sscreening
Minimise harms of screening, maximise benefits of screening by: increasing screening uptake, optimising test performance, optimising effectiveness of post screening therapy
Potential negative effects from participating in screening
false positive, false negative, correctly identified as having disease
How to ensure screening is ethical
Benefits>harm
Resources used efficiently
Autonomy respected
Equity (fairness) promoted)
