Screening Flashcards
What are the positives of screening?
Identifies disease sooner
Improve patient outcome via treatment
Early diagnosis and treatment
Reduce risk of disease/complications
What conditions are screened for in the UK?
AAA, bowel cancer, breast cancer, cervical cancer
What four criteria must be met for approval for screening?
Disease/condition aspects
Test aspects
Treatment aspects
Programme aspects
What are the disease aspects?
Important health problem
Understand epidemiology and natural Hx
Early to detect
Cost-effective intervention
What are the test aspects?
Simple Safe Precise Valid Acceptable to patients Know % of +ve/-ve test Defined level of +ve cut off
What are the treatment aspects?
Effective evidence-based treatment
Early treatment is advantageous
Policy on who to treat
Good availability of treatment
What are the programme aspects?
Proven as effective
Counselling available
Diagnosis facilities
Define diagnosis
A definitive identification of suspected disease by application of tests, exams or other extensive procedures to definitively label people as having a disease or not
What are some general cons of screening?
Cause anxiety Reduced QoL by treatment Treating something that may not have caused problems Drain resources Risks of screening
What is sensitivity?
Good at detection (out of disease present, how many have it)
What is specificity?
Good at showing well people are well (out of disease absent, how many test negative)
What is positive predictive value?
If have positive test, how likely is it that they have disease
What is negative predictive value?
If have negative test, how likely is it they don’t have the disease
How will sensitivity, specificity, PPV and NPV be affected by population size or prevalence?
Sensitivity and specificity are values of test so unaffected
Low prevalence -> low PPV as lots of false +ves
What are false positives and negatives?
False +ve is a +ve test but person doesn’t have disease
False -ve is a -ve test but person does have disease
What are the rules for working out equations?
Always have true positive or negative on top
Whatever was on top line must be on bottom
Bottom line must have true and false on it
PPV has all positives in it so true pos/true pos plus false pos
NPV has all negatives in it
Give three types of bias that can occur in screening
Lead time: find disease earlier so looks like you prolonged life but actually just prolonged how long you know about it
Length time: find slow progressing diseases that were unlikely to cause a problem
Selection: people who care more about their health are more likely to go for screening even though they are more likely to be healthy
Define screening
A systematic attempt to detect an unrecognised condition by application of tests, exams or other procedures which can be rapidly applied to distinguish if apparently well people have a disease or not
Quick and cheap test-> screen +ve/-ve -> high/low risk -> tests
What are the five main issues of screening?
Alters patient-doctor contact Complexity of screening programmes Evaluating screening programmes Limitations of screening Sociological critiques of screening
What are the limitations of screening?
Potential for error so false +ve/-ve cause anxiety or complacency
GPs paid to do screening
Over-diagnosis
What are the sociological critiques of screening?
Structural: patients responsibility so someone with mental illness may be unable to participate
Surveillance: always being watched and controlled
Social constructionist: non attendance=deviant
Feminist: more targeted to men than women
