Population Based Screening Flashcards
What is opportunistic case finding?
Patient presents with Sx
HCPs check for other conditions and find something
Define diagnosis
Definitive identification of a suspected disease or defect by application of tests, examinations or other procedures to definitely label people as either having a disease or not
Define screening
Systematic attempt to detect an unrecognised condition by the application of tests, examinations or other procedures
What is the purpose of screening?
To give a better outcome compared with finding something in the usual way - waiting for Sx
What do we need to consider about the condition we want to screen for?
Must be important health problem - frequency and severity
Natural Hx must be understood
All cost-effective primary prevention interventions should have been implemented as far as practicable
Screening is what stage of prevention?
Secondary prevention
What must we consider about the test we want to use for screening?
Simple, safe, precise and validated
Cannot give risks to asymptomatic people
Must be an agreed cut off level
What are some of the problems with screening tests?
False positives - stress, anxiety, inconvenience
False negatives - inappropriate reassurance, may delay presentation with Sx
What is the sensitivity of a test?
Proportion of people with the disease who test positive
A.k.a detection rate
True positives / true positives and false negatives
(/All the people who actually have the disease)
What is the specificity of a test?
The proportion of people without the disease who test negative
Correctly identified as not having the disease
True negatives / true negatives and false positives
What is the positive predictive value?
If I test positive - what is the chance that I actually have the disease?
True positives / true and false positives
What is the negative predictive value?
Proportion of people who test negative who actually do not have the disease
True negatives / true and false negatives
Describe lead time bias
Early diagnosis falsely appears to prolong survival
The people don’t actually live longer, they just live longer knowing they have the disease
What is length time bias?
Screening programmes are better at picking up slow-growing, unthreatening cases
More likely to have a favourable prognosis therefore may never have even caused a problem
Describe selection bias for screening
Skewed by health volunteer effect
People having regular screening are likely to be doing other health-protective things
