Flashcards in Screening Deck (14):
What are some conditions required for screening?
1968 prerequisites by Junger
- important public health problem
- accepted treatment
- latent phase of disease
- natural history understood
- cost effective
- cut off point on who to treat
What diseases are suitable for screening?
Must be relatively common w severe consequences
Have latent phase
Early treatment has advantage over later
Screening has net benefit
What is lead time bias?
Increase in survival in screened population may just be because of earlier diagnosis (death after disease onset may not actually change)
What is length bias?
Screening more effective in indolent diseases (not aggressive)
With aggressive diseases, patient would have died before screening
Hence survival following screening may just be due to less aggressive nature
The grid for false negatives etc
a= true p
B= false p
C= false n
D = true n
What is the PPV + NPV?
Positive predictive value: proportion of those who tested positive who actually have condition (a/a+b)
Negative predictive value: proportion of those who tested negative that actually don’t have condition (d/d+c)
What does a lower PPV indicate?
Rare condition - not many people actually have disease and there are lots of false positives
Sensitivity vs specificity
Sensitivity: proportion of those who have condition that tested positive (a/a+c)
Specificity: proportion of those who don’t have condition that tested negative (d/b+d)
What cancer screening programmes are available in England?
Breast, cervical, bowel
Describe the NHS breast screening programme
Screening every 3 yrs for 50-70
Being extended to 47-53 in England
Women over 70 can request it
V high NNT (400 screened over 10yrs so 1 less woman will die)
What is a disadvantage of breast screening?
20% of detected cancers are actually DCIS (benign lesions, normally not palpable)
Hence lots of false positives + unnecessary further investigation + treatment
Benefits of breast cancer screening
20% reduction in risk of dying from breast cancer compared to w/o programme
~ 1300 deaths prevented per year
What is the uptake of breast screening in UK? How can this be improved?.
93% from cross sectional survey of private households
- simple information provision
- our of hours appointments
- provision of transport (lower uptake in low socio economic groups)
- follow up of non attendees to address concerns + give info