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Flashcards in Prevention and screening revision Deck (20):

What is primary prevention? What are the two types?

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

High risk approach and population approach


What is secondary prevention?

2 things:
(1) early detection and treatment of a disease in at an early stage (e.g. breast cancer screening)
(2) Preventing the recurrence of a disease that has occurred (E.g. aspirin in MI)


What is tertiary prevention?

Preventing worsening symptoms and complications of an existing disease e.g. post-stroke rehabilitation

treatment + rehabilitation


What are the two approaches to (primary) prevention?

1. population approach
2. High-risk approach


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 to decrease BP, 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. QRISK2 --> >10% given statin


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)


What is lead time bias?

The time between early diagnosis with screening and the time in which diagnosis would have been made without screening

Apparent increase in survival time

♣ Patients A+B get a disease at the same time
- Patient A engages with screening and picked up earlier
♣ Patient B doesn’t and picked up at symptomatic stage (later on)
♣ Both A and B die at the same time
♣ Appears to prolong survival time when actually it doesn’t


What is length-time bias?

Disease that progress more slowly is more likely to be picked up by screening rounds than more rapidly progressing diseases


Give some types of screening?

Population based screening (e.g. Cervical)
Opportunistic screening (chlamydia)
Screening for communicable disease (e.g. mootness or IGRA in contacts of someone with TB)


what are some disadvantages to screening?

False +ves - unnecessary tests (harmful) + undue anxiety

+ve test leads to Distressing and harmful diagnostic tests

Detection and treatment of sub-clinical disease which may have never caused any problem

-ve results may mean that if a woman developed a lump she wouldn't get it checked


What are the NPV + PPV dependent on?


if the prevalence is higher, the NPV is lower and the PPV is higher


What are the two screening criteria?

Wilson and Jungner



give some types of bias seen in screening

Selection bias (E.g. those with FHx more likely to attend screening or more educated)

lead time bias

length time bias