3 Secondary prevention

Question 1

What is screening?

Answer 1

process of identifying healthy people who may be at increased risk of a disease or condition.

Question 2

What may screening lead to early detection of?

Answer 2

disease (breast cancer)
pre-cursor to disease (CIN for cervical cancer)
susceptibility to disease (cardiovascular risk assessment)

Question 3

Why might we shift the cut-off further left?

Answer 3

to avoid missing disease (sensitivity)

Question 4

Why might we shift the cut-off further right?

Answer 4

to avoid misclassifying healthy people (specificity)

Question 5

What is sensitivity?

Answer 5

The rate of True positives

the proportion of diseased people identified as diseased

Question 6

What is specificity?

Answer 6

the rate of true negatives

proportion of healthy people identified as healthy

Question 7

what is a specific test useful for?

Answer 7

screening where consequences of missclassifying someone falsely as diseased are serious

Question 8

What is a sensitive test useful for?

Answer 8

screening where consequences of missclassifying disease are serious

Question 9

What is the positive predictive value?

Answer 9

the number of true positives out of all of those who tested positive

if you test positive how likely is it that you’ve got the disease

Question 10

What will screening in a low risk population cause?

Answer 10

more false positives

Question 11

What is prevalence of a disease?

Answer 11

the number of positive tests in a cohort (inc. false positives)

Question 12

What is the relationship between PPV / NPV and prevalence?

what is the significance of this?

Answer 12

As prevalence increases, PPV goes up and stays up

NPV stays quite high nutil very high prevalence, where it will decrease

usually it is the PPV that is changing, but the NPV stays high for most circumstances

Question 13

What is the difference between a screening test and programme?

Answer 13

a programme takes things further than a test, with comprehensive disease control activity following a positive result

Question 14

What is the role of the National Screening Committee?

Answer 14

advises ministers on all aspects of screening policy, assesses new screening programmes to ensure they do more good than harm

Question 15

What is there to lose with a false negative?

Answer 15

false reassurance
disregard symptoms
delayed intervention

Question 16

What is there to lose with a false positive?

Answer 16

further test costs
risk of diagnostic testing
anxiety
fear of future screening

Question 17

What is the significance of natural disease history?

Answer 17

understanding natural disease history is essential to screening

we therefore need:
preclinical detectable period
test that can be applied
treatment that will alter outcome

Question 18

What conditions are required to undertake screening according to the NSC?

Answer 18

important
has a latent phase
natural hisotry understood
primary prevention implemented

Question 19

What criteria does the screening test have to meet according to the NSC?

Answer 19

suitable
agreed suitable cut-offs
agreed policy for test +ve

Question 20

What criteria does the screening intervention have to meet according to the NSC?

Answer 20

effective treatment
policy on who to treat
adequate facilities

Question 21

What criteria does the screening programme have to meet according to the NSC?

Answer 21

RCT evidence of effectiveness
information understandable to those screened
clinically, socially, and ethically acceptable
benefits > harms

Question 22

What was the result of thyroid cancer screening in South Korea?

Answer 22

the rapid increase in thyroid cancer diagnoses were not accompanied by an reduction in deaths

screening did not outweigh the harms of the process

Question 23

What are the 3 main types of bias associated with screening programmes?

Answer 23

volunteer bias
lead time bias
length bias

Question 24

What type of bias is associated with volunteer bias?

Answer 24

detection bias leading to pseudodisease

detection of a disease precursor by screening in someone who would not ultimately develop symptoms

Question 25

What is lead time bias?

Answer 25

time between disease detection through screening and the disease detection by diagnosis without screening

Question 26

What is length bias?

Answer 26

those with long-preclinical phase more likely to be detected by screening, and usually have better prognosis (less aggressive disease)

Question 27

What was found by the Nelson trial?

Answer 27

more early stage and fewer later stage cancers in low dose CT vs control

There was no overally difference between the 2 ggroups in all-cause mortality, the response has been mixxed. The US and UK have not implemented this screening process, Croatia have

Question 28

What were the potential harms from screening observed in the Nelson trial?

Answer 28

9.2% of low-dose CT screening tests were interderminate and had to be repeated
56%% of those with a positive test were false positive