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
- screening
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
