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04 - PASS 1 > S5) Population-based Screening > Flashcards

S5) Population-based Screening Flashcards

1
Q

How can we detect diseases?

A
  • Spontaneous presentation
  • Opportunistic case finding
  • Screening
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2
Q

Define diagnosis

A

Diagnosis is the definitive identification of a suspected disease or defect by application of tests, examinations or other procedures to definitely label people as either having a disease or not having a disease

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3
Q

What is screening?

A

Screening is a systematic attempt to detect an unrecognised condition by the application of tests, examinations, or other procedures to identify healthy people who may be at increased risk of disease or condition

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4
Q

Outline the screening process

A
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5
Q

What is the purpose of screening?

A

To give a better outcome compared with finding something in the usual way (having symptoms and self reporting to health services)

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6
Q

One of the criteria for implementing a screening programme is Condition.

Explain this

A

Condition: an important health problem (frequency/severity) with epidemiology, incidence, prevalence and natural history understood

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7
Q

One of the criteria for implementing a screening programme is Test.

A screening test is going to make two types of error: false positive and false negative. What are these?

A
  • False positive – refers well people for further investigation, putting them through stress, anxiety and inconvenience

- False negative – fails to refer people who have an early form of the disease, inappropriately reasurring them

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8
Q

What are the four features of test validity?

A
  • Sensitivity
  • Specificity
  • Positive predictive value
  • Negative predictive value
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9
Q

What is sensitivity?

A

Sensitivity is the proportion of people with the disease who test positive (aka detection rate)

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10
Q

What is specificity?

A

Specificity is the proportion of the people without the disease who test negative

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11
Q

What is positive predictive value?

A

Positive predictive value is the probability that someone who has tested positive actually has the disease

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12
Q

What influences PPV?

A

Positive Predictive Value is strongly influenced by the prevalence of the disease

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13
Q

What is negative predictive value?

A

Negative predictive value is the proportion of the people who test negative and actually do not have the disease

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14
Q

What are the implications of false positive results?

A
  • Offered diagnostic testing with all its anxieties and risks for an absent condition
  • May lead to lower uptake of screening in future and greater risk of interval cancer
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15
Q

What are the implications of false negative results?

A
  • Not offered diagnostic testing when in fact they may have benefited from it
  • False reassurance – may present late with symptoms as a consequence
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16
Q

One of the criteria for implementing a screening programme is Intervention.

Explain this

A
  • Effective intervention for patients identified through screening

- Intervention at a presymptomatic phase leads to better outcomes for the screened individual

17
Q

One of the criteria for implementing a screening programme is Screening programme.

Explain this

A
  • Screening programmes have proven effectiveness in reducing mortality or morbidity
  • Benefit gained should outweigh any harms e.g. overdiagnosis, overtreatment, false positives, false reassurance, uncertain findings and complications
18
Q

One of the criteria for implementing a screening programme is Implementation.

Explain this

A
  • Clinical management and patient outcomes should be optimised
  • Evidence-based information available to potential participants (informed choice)
  • Public pressure should be anticipated
19
Q

Identify 2 advantages of screening for disease

A
  • Detect many diseases at birth, with no risk to the child
  • Avoid serious and permanent consequences for the child (presymptomatic treatment)
20
Q

Identify 4 disadvantages of screening programmes

A
  • Specimens may need to be taken a second time
  • False positives
  • False negatives
  • Complications could still arise
21
Q

One evaluation difficulty is lead time bias.

What is this?

A
  • Lead time bias is when early diagnosis falsely appears to prolong survival
  • Screened patients appear to survive longer, but only because they were diagnosed earlier
22
Q

One evaluation difficulty is length time bias.

What is this?

A

Length time bias involves the easy detection of slow growing, unthreatening cases rather than aggressive, fast-growing ones

23
Q

Another evaluation difficulty is selection bias.

What is this?

A
  • 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
24
Q

Give examples of 4 screening programmes in the UK

04 - PASS 1 (17 decks)

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