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Flashcards in Prevention and screening revision Deck (17):

What is primary prevention?

Preventing the onset of disease (e.g. vaccination)


What is secondary prevention?

Interventions aimed at early detection and treatment, such as screening, and those aimed at minimising the effect of a health event that has occurred (e.g. aspirin after an MI, mammography screening to detect early stage breast cancer)

i.e. disease already exists but in early stages - preventing complications

Important to understand that secondary prevention involves screening + early diagnosis


What is tertiary prevention?

Preventing worsening symptoms and complications of an existing disease e.g. cardiac rehabilitation, diabetic nurses)

treatment + rehabilitation


What's a good way to remember the 3 types of prevention?

PTS: Prevention, Screening, Treatment


What are the two approaches to prevention?

1. population approach
2. High-risk approach

both are based on the risk factor distribution curve


What is the population approach to prevention?

A preventative measure
delivered on a population wide basis and seeks to
shift the risk factor distribution curve

E.g. dietary salt reduction through legislation, working with the food industry and advice to the general public should shift the blood pressure distribution curve to the left (or sugar tax - weight distribution curve shifted to left)


What is the high-risk approach to prevention?

The high risk approach seeks to identify individuals above a chosen cut-off and treat them

e.g. screening for people with high blood pressure and treating them


What is the prevention paradox?

Preventive measure which brings much benefit to the population often offers little to each participating individual


What is screening?

A process which sorts out apparently well people who probably have a disease (or precursors or susceptibility to a disease) from those who probably do not

Not dianostic


What is the criteria (Wilson and Jungner) for screening?

The condition:
- Improtant health problem
- Latent/pre-clinical phase
- Natural Hx known

Screening test:
- Acceptable
- Suitable (sensitive, specific, inexpensive)

- effective
- agreed policy on whom to treat

Organisation + costs:
- Facilities
- costs +benefits
- ongoing process


What is sensitivity?

The proportion of people w/ the disease who are correctly identified by the screening test

true +ves / (true +ves + false -ves)


What is specificity?

The proportion of people without the disease who are
correctly excluded by the screening test

True -ves / (true -ves + false +ves)


What is PPV?

The proportion of people w/ a positive test who actually have the disease

True + / (True +ve + false +ve)


What is NPV?

The proportion of people w/ a negative test who don't have the disease

True - / (True -ve + false -ve)


Why is the PPV value so different?

Predictive values are dependent on underlying prevalence

(sensitivity + specificity are not)


What is lead time bias?

Lead time is the length of time between the detection of a disease and its usual clinical presentation and diagnosis

I.e. the time between early diagnosis with screening and the time in which diagnosis would have been made without screening


What is length-time bias?

A form of selection bias

Cancers may be slowly or rapidly progressive

Less aggressive cancers are more likely to be detected by screening rounds

Screening picks up less aggressive cancers (more likely)