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HaDSoc > 6: screening > Flashcards

6: screening Flashcards

1
Q

define screening

A

A SYSTEMATIC attempt to DETECT an unrecognised
condition by the application of tests, examinations, or
other procedures, which can be applied RAPIDLY (and
cheaply) to DISTINGUISH between APPARENTLY well
persons who PROBABLY have a disease (or its precursor)
and those who probably DO NOT

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2
Q

list the criterias for screening

A
  1. Condition
  2. Test
  3. Intervention
  4. Screening programme
  5. Implementation
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3
Q

list the criteria for implementation of a screening programme, including those relating to the condition (disease)

A
  • An IMPORTANT health problem (frequency/severity)
  • epidemiology, incidence, prevalence and natural history WELL UNDERSTOOD
  • cost-effective PRIMARY PREVENTION interventions must have been considered
  • must have EARLY DETECTABLE STAGE
  • psychological implications should be understood
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4
Q

list the criteria for implementation of a screening programme, including those relating to the test

A
  • Simple, safe, precise and validated screening test
  • Agreed cut-off level must be defined and agreed
  • Acceptable to target population
  • Agreed policy on further diagnostic investigation for those who test positive and choices available to them
  • Distribution of results within population must be known
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5
Q

list the criteria for implementation of a screening programme, including those relating to the treatment

A
  1. Based on evidence
  2. Early treatment must be advantageous
  3. Clinical management and patient outcomes should be optimised
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6
Q

list the criteria for implementation of a screening programme, including those relating to the programme

A
  1. benefit should outweigh harm
  2. facilities for screening / counselling / treatment
  3. proven effectiveness (RCT data)
  4. decision on perimeter should be scientifically justifiable to the public
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7
Q

what are the difficulties of evaluating the effectiveness of screening programmes?

A

lead-time bias
length-time bias
selection bias

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8
Q

what is lead-time bias?

A

early diagnosis falsely appear to prolong survival, but patient lives the same length of time

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9
Q

what is length-time bias?

A

screening programmes are better at picking up slow-growing, unthreatening cases than aggressive, fast-growing ones
disease detectable through screening are more likely to have a favourable prognosis

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10
Q

what is selection bias?

A

‘healthy volunteer effect’
• Studies of screening often skewed by ‘healthy volunteer’ effect
• Those who have regular screening likely to also do other things that protect them from disease

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11
Q

how do you get rid of selection bias?

A

• An RCT would help deal with this bias

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12
Q

list the criteria for implementation of a screening programme, including those relating to the implementation

A

• Clinical management and patient outcomes should be
optimised
• All other options for managing the condition should have been considered
• Management and monitoring programme – quality assurance
• Adequate staffing and facilities for programme
• Evidence-based information available to potential
participants (informed choice)
• Public pressure should be anticipated - decisions should be scientifically justifiable to the public

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13
Q

what are the challenges of implementing a screening programme?

A
  1. alters doctor-patient relationship
  2. complexity of screening programmes need to be taken into account
  3. evaluation of screening programmes difficult
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14
Q

Difficulty in achieving informed choice in screening programmes?

A

• Communicating benefits, harms and risks of preventive

interventions can be challenging

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15
Q

Sociological critiques of screening?

A
  • Structural critiques
  • Surveillance critiques
  • Moral obligation
  • Feminist critiques
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16
Q

what are feminist critiques of screening?

A

screening is targeted more at women

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17
Q

what are Surveillance critiques surrounding screening?

A

Individuals and populations increasingly subject to

surveillance – prevention as social control?

18
Q

what are structural critiques surrounding screening?

A

Victim blaming / Individualising pathology

19
Q

give examples of screening programmes in the UK

A

BBC: breast, bowel, cervix
AAA (abdominal aortic aneurysm)
diabetic eyes
newborn spot blood test

20
Q

what are the 2 types of errors that screening test will make?

A

false positive

false negative

21
Q

what is a false positive?

A

refer well people for further investigation

22
Q

what is a false negative?

A

fail to refer people who do actually have an early form of the disease

23
Q

what are the problems with referring well people for further investigation? (false positive)

A
  • Put them through stress, anxiety, inconvenience
  • Direct costs
  • Opportunity costs
24
Q

what are the problems of failing to refer people who do actually have an early form of the disease? (false negative)

A
  • Inappropriate reassurance

* Possibly delay presentation with symptoms

25
Q

what are the features of test validity?

A
  • Sensitivity (detection rate)
  • Specificity
  • Positive predictive value
  • Negative predictive value
26
Q

what is sensitivity of the test?

A
  • The proportion of the people WITH the disease who are test POSITIVE
  • Also know as the DETECTION RATE
  • The proportion of the people who really have the disease who are identified correctly by the test as having the disease
  • the probability a case will test positive
27
Q

how do you work out sensitivity of the test?

A

Sensitivity = True positives / (True positives + false negatives)

28
Q

what does it mean if the sensitivity of the test is high?

A

• the test is very good at correctly identifying people with the disease you are screening for
• A high sensitivity is ideal (although not always possible)
(sensitive to disease)

29
Q

what is specificity of the test?

A

• the proportion of the people WITHOUT the disease who
are test NEGATIVE
• The proportion of the people who really do not have the
disease who are identified correctly by the test as not having the disease
• Probability a non-case will test negative
(specific to accuracy)

30
Q

how do you work out specificity?

A

Specificity = True negatives / (false positives + true negatives)

31
Q

what does a high specificity mean?

A
  • the test is very good at correctly identifying people without the disease as not having the disease
  • A high specificity is ideal (although not always possible)
32
Q

what should be expected if the same test is applied in the same way to different populations with regards to sensitivity and specificity? why?

A

• When the same test is applied in the same way in different populations the test will have the SAME sensitivity and specificity
• Sensitivity and specificity are a function of the
CHARACTERISTICS of the test

33
Q

what is positive predictive value (PPV)?

A

Probability that someone who has tested POSITIVE actually HAS the disease

“If I am test positive – what is my risk of actually having the disease?”

34
Q

what is PPV strongly influenced by?

A

prevalence of the disease

35
Q

how do you work out PPV?

A

PPV = True positives / (True positives + false positives)

36
Q

what is the negative predictive value (NPV)?

A

the proportion of the people who are test negative who actually do not have the disease

“If the screening test is negative – what are the chances
that I really don’t have the disease?”

37
Q

how do you work out NPV?

A

NPV = True negatives / (False negatives + True negatives)

38
Q

what does a false positive result indicate?

A

patients MAY have the disease when in fact they do not

39
Q

what are implications of false positive results?

A

• Patients will be offered (invasive) diagnostic testing with associated anxieties and risks – They will be turned into “patients” when they are not actually ill
• May lead to lower uptake of screening in future
• If the PPV is low there will be a lot of people with false
positive results who undergo stress and unnecessary
procedures

40
Q

what does false negative indicate?

A

the screening test indicates that they do not have the disease when in fact they do

41
Q

implications of false negative results?

A

• Patients will not be offered (invasive) diagnostic testing
when in fact they may have benefited from it. Their
disease, although present will not be diagnosed.
• They will be falsely reassured – may present late with
symptoms as a consequence

HaDSoc (9 decks)

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