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Epidemiology and Biostatistics > Screening > Flashcards

Screening Flashcards

1
Q

Definition of screening

A

Actively identifying disease/pre disease in apparently healthy subjects who may benefit from early treatment

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2
Q

Definition of opportunistic screening

A

When someone asks their doctor for a test

This type of screening is not always checked/monitored

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3
Q

Definition of population screening

A

Entire population at risk is called to be screened

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4
Q

Definition of the lead time bias

A

Interval between the diagnosis of a disease at screening and the usual time of diagnosis by symptoms
As a result, screen detected cases appear to survive longer

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5
Q

Definition of length biased sampling

A

Rapidly progressive disease causes the individual to consult but less rapidly progressing cases are likely to remain for screening

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6
Q

Definition of selection bias

A

Those who enter screening almost invariably are more conscious than those who decline

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7
Q

Definition of over diagnosis bias

A

Signs detected and identified as disease in a screening program would not have presented clinically during the individuals lifetime

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8
Q

What is screening and what does it not involve

A

Actively identifying disease/pre disease in apparently healthy subjects

Does not involve

  • testing
  • case finding
  • opportunistic screening
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9
Q

What is the difference between screening and a diagnostic test

A

Screening
-No symptoms of condition but disease onset has occured

Diagnostic test
-Confirm/deny suspected condition once initial testing has revealed its possibility

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10
Q

What is the difference between primary and secondary prevention

Is screening a form or primary or secondary prevention

A

Primary prevention

  • Whilst you’re healthy, prevent onset of disease
  • eg, cholesterol lowering drugs to prevent heart disease

Secondary prevention

  • Once diseased, prevents it from getting worse, but before diagnosis
  • eg screening
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11
Q

What are the 4 types of screening that the NHS offers

What pathologies can be tested

A

Cancer

  • Breast
  • Cervical
  • Bowel

Cardiovascular

  • AAA
  • Diabetic retinopathy

Antenatal

  • SCD and thalassemia
  • Downs
  • Ultrasound for congenital deformities

Newborns

  • SCD, CF
  • Congenital hypothyroidism, inherited metabolic diseases
  • Hearing and physical tests
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12
Q

Describe the importance of bowel cancer screening

A

Most cases of bowel cancer are detected in the muscular external and lymph nodes
Decreased 5% year of survival

So by screening, more cases are detected in the mucosa where the 5% year survival is high

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13
Q

What are the 3 criteria for screening for a disease

Condition

A
  • Condition affects large frequency/rare but has a large impact on individuals
  • Primary prevention not possible/effective
  • Identifiable preclinical stage of disease
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14
Q

What are the criteria for screening for a disease

Test

A
  • Must be able to separate those with a high probability of the disease from those with a low probability
  • Simple, safe, precise and validated
  • Clear distinction between normal and abnormal results
  • Acceptable to subjects, reasonable costs
  • Agreed policy on further diagnostic investigation of individuals with a +ve result
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15
Q

What are the properties of a screening test, what are the 4 possible results

What are the 4 calculations you can do to test for the efficacy of the test

How does prevalence affect the calculations

A

TP, FP
FN, TN

Sensitivity
Specificity

PPV
NPV
-if prevalence falls, PPV falls and ratio between TP:FP falls

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16
Q

Describe the Receiver Operating Curve

What is the ideal ROC

A

If ratio of TP:FP is equal => not useful

Ideally you’d like ROC to be as close to LH corner => increased specificity and sensitivity

17
Q

What is the criteria for screening for a disease

Treatment

A

-Effective treatment available. Outcome of early treatment better than later treatment after clinical diagnosis

18
Q

What is lead time bias

A

Interval between the diagnosis of a disease at screening and then usual time of diagnosis by symptoms

19
Q

What are the 4 types of bias that can arise in a screening test

A

Lead time bias
Length bias
Selection bias
Overdiagnosis bias

20
Q

What is length bias

A

Slow growing tumors may be more often detected through screening
Rapidly progressive diseases cause the individual to consult but less rapidly progressive cases to remain for screening detection

21
Q

What is selection bias

A

Those who enter screening are more conscious than those who decline

22
Q

What is over diagnosis bias

A

+ve screening results does not lead to the development of disease in the individuals lifetime

23
Q

What are the solutions to these biases

A

RCT when mortality is used as the outcome instead of survival
Survival can be used if there is evidence of over diagnosis bias and observation period is from randomization date
Individual and community trials

24
Q

What are the 5 properties of a good screening programme

A

Evidence that the program is clinically, socially and ethically acceptable to health professionals and the public

Benefits should outweigh physical and psychological harms of programme

Opportunity cost should be balanced in relation to total expenditure on medical care

Plan for managing and monitoring the screening programme and quality

Adequate staffing and facilities fo the whole programme

25
Q

What are the 4 advantages of screening

A

Improved prognosis for TP
Less radical treatment needed
May save resources
Reassure those with TN

26
Q

What are the 5 disadvantages of screening

A

Longer period of awareness for TP whose prognosis is unaltered
Overtreatment of borderline abnormalities
False reassurance of FN
Anxiety and hazards for FP
Hazard of test to all participants

27
Q

What is quality assurance and why is it important in a screening test

How is this done

A

Minimise harms, maximize benefits from screening

  • increase screening uptake
  • optimise test performance so sensitivity and specificity is high as possible
  • optimise effectiveness of post screening therapy
28
Q

What are failsafe actions

A

At all stages of screening, different healthcare workers have different responsibilities to ensure that any +ve results are handled accoridngly

29
Q

What are the ethical considerations that need to be made in screening

A

Those invited are not patients
Must get informed consent

Negative outcomes from participating in a screening programme are possible

  • FP
  • FN
  • TP

The benefits must exceed harms
Efficient resource usage
Autonomy and equity must be promoted

30
Q

What are the inequalities associated un screening uptake

A

More affluent groups are more likely to engage in screening programs (no of cars etc)
Creates health inequalitiy as less affluent groups are more ;likely to have worse health outcomes

Epidemiology and Biostatistics (16 decks)

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