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Flashcards in Population Based Screening Deck (23)
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what is opportunistic case finding

when a person presents themselves with symptoms and the health professional takes the opportunity to look for other potential conditions


define diagnosis

definitive identification of a suspected disease by application of tests and examinations to label the person to having a disease or not


what are the 3 ways to detect a disease

- spontaneous presentation
- opportunistic finding


what is screening

attempt to detect an unrecognised condition through examinations and procedures which are applied rapidly and cheaply to identify who probably has a disease and who probably doesn't


what is the purpose of screening

- to give a better outcome compared to finding the disease in the usual way


what are the 5 areas of criteria for screening programmes

- condition
- test
- intervention
- screening programme
- implementation


in order to have a screening programme what must the be condition be like

- important health problem
- understood history, prevalence and incidence
- cost effective primary prevention


in order to have a screening programme what must the test be like

- simple, safe and precise
- acceptable
- agreed on cut off points and points for further investigation


what errors do screening tests have

- referring well people for further investigation = false positive
- fail to refer diseased people = false negative


what is the sensitivity/detection rate of a test

the proportion of people with the disease who test positive. the probability a case will test positive


how do you calculate the sensitivity of a test

true positives / true positives + false negatives


what does a high sensitivity mean

the test is good for identifying people with the disease


what is test specificity

the proportion of people without the disease who are test negative
probability a non case will test negative


what is test specificity equal to

true negatives/ false positives + true negatives


what does a high test specificity mean

the test is good at identifying people without the disease


what is the positive predictive value

the risk of actually having the disease if you test positive


what is PPv equal to

true positives/ true positives + false positives


how does PPV change with prevalence

in a high prevalence PPV is also very high but in a low prevalence population screening gives a low PPV


what is negative predictive value

the proportion of people who are test negative and really don't have the disease


what is NPV equal to

true negatives/ false negatives+true negatives


what are the implications of false positive results

- invasive diagnostic tests
- anxiety
- lower uptake of screening in the future


what are the implications for false negatives

- not offered diagnostic testing which they would have benefitted from
- falsely reassured


what are some of the evaluation difficulties of screening programmes

- early diagnosis falsely appears to prolong life
- disease detected through screening are more likely to have a favourable prognosis
- those who attend regular screening are more likely to live a healthy lifestyle