Prevention and screening revision Flashcards
(20 cards)
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?
- 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)
Treatment:
- 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)
Pre-employment
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?
prevelance
if the prevalence is higher, the NPV is lower and the PPV is higher
What are the two screening criteria?
Wilson and Jungner
WHO
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
