Population Based Screening

Question 1

what is opportunistic case finding

Answer 1

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

Question 2

define diagnosis

Answer 2

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

Question 3

what are the 3 ways to detect a disease

Answer 3

• spontaneous presentation
• opportunistic finding
• screening

Question 4

what is screening

Answer 4

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

Question 5

what is the purpose of screening

Answer 5

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

Question 6

what are the 5 areas of criteria for screening programmes

Answer 6

• condition
• test
• intervention
• screening programme
• implementation

Question 7

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

Answer 7

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

Question 8

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

Answer 8

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

Question 9

what errors do screening tests have

Answer 9

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

Question 10

what is the sensitivity/detection rate of a test

Answer 10

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

Question 11

how do you calculate the sensitivity of a test

Answer 11

true positives / true positives + false negatives

Question 12

what does a high sensitivity mean

Answer 12

the test is good for identifying people with the disease

Question 13

what is test specificity

Answer 13

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

Question 14

what is test specificity equal to

Answer 14

true negatives/ false positives + true negatives

Question 15

what does a high test specificity mean

Answer 15

the test is good at identifying people without the disease

Question 16

what is the positive predictive value

Answer 16

the risk of actually having the disease if you test positive

Question 17

what is PPv equal to

Answer 17

true positives/ true positives + false positives

Question 18

how does PPV change with prevalence

Answer 18

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

Question 19

what is negative predictive value

Answer 19

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

Question 20

what is NPV equal to

Answer 20

true negatives/ false negatives+true negatives

Question 21

what are the implications of false positive results

Answer 21

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

Question 22

what are the implications for false negatives

Answer 22

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

Question 23

what are some of the evaluation difficulties of screening programmes

Answer 23

• 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