Screening Flashcards
What is primordial prevention
Target population and focus on social and environmental intervention e.g. improving housing, ban indoor smoking
What is primary prevention
Target population or individual, prevent disease before emerging, target healthy people e.g. sunscreen, smoking cessation
What is secondary prevention
Target individuals with subclinical diseases to catch them early e.g. screening programs for cancer, dental checks
What is tertiary prevention
Target clinical and outcome stages, reduce severity and complications e.g. stroke rehab
What is quartenary prevention
Target patients at risk of over medicalisation -prevent harmful medical intervention
Screening principles
It must be an important problem, treatable, have a suitable test which is acceptable to the population
Screening tests
Detect potential for disease, large number of people at risk, simple and not harmful, high sensitivity, suspicion of disease
Screening aims
To reduce mortality
Diagnostic tests
Establish presence of disease, high specificity, definite diagnosis
Screening program flow diagram
Identify population, give information, test, referral of positive cases, diagnosis, treatment, reporting of outcomes
Four types of screening
Population based, selective, multifaceted, opportunistic
Population based screening
Done systematically on the whole population
Selective screening
Targets particular subset of population
Multifaceted screening
More than one test
Opportunistic screening
During routine healthcare checks e.g. blood pressure
NHS screening programs examples
Abdominal aortic aneurysm, cancer (breast, bowel, cervical), Antenatal (hearing, physical, bloodsport, infectious diseases), diabetic eye disease and sickle-cell
Opportunistic test examples
Chlamydia test, atrial fibrillation, blood pressure
Inplementation of screening is done by
Public-health England, national screening committee, UKHSA
Issues of screening
Course, ensure people have informed choices
Assess the performance of a test using
Sensitivity, specificity, accuracy
What is sensitivity
True positives
What is specificity
True negatives correctly identified
What is accuracy
The proportion of true positives and true negatives
PPV
Probability of having condition given a positive test
Decrease in prevalence causes
Decrease in PPV
PPV influenced by
Sensitivity and specificity 
If PPV is high a high proportion of people tested
Positive
What is NPV
Probability being disease-free given a negative test
Low prevalence equals a 
High NPV
There are more true negatives than there are
False negatives
Sensitivity equation
TP/TP+FN
Specificity equation
TN/TN+FN
PPV equation
TP/TP+FP
NPV equation
TN/TN+FN
