Session 6 - Screening Flashcards Preview

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Flashcards in Session 6 - Screening Deck (21)
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1
Q

Define screening

A

Systematic attempt to detect an unrecognised condition by use of tests, exams etc which can be applied rapidly to distinguish between persons with and without the disease

2
Q

What are the 3 ways a disease can be detected?

A
  1. Spontaneous presentation
  2. Opportunistic case finding
  3. Screening
3
Q

What must the disease be for a screening program to be implemented?

A
  • Must be an important health problem
  • Epidemiology and natural history must be well understood
  • Must have an early detectable stage
  • Cost-effective primary prevention interventions must have been considered and where possible implemented
4
Q

What must the test be for the screening program to be implemented?

A
  • Simple and Safe
  • Precise and valid
  • Acceptable to the population
  • There must be an agreed policy on whom to investigate further
5
Q

What must the treatment be for a screening program to be implemented?

A
  • Effective evidence based treatment must be available
  • Early treatment must be advantageous, must not just bring forward the date of diagnosis
6
Q

What must the programme be for the screening to be implemented?

A
  • Other options considered, e.g. improving treatment
  • Benefit should outweigh physical and psychological harm
  • Facilities for diagnosis and treatment
7
Q

What is a false positive?

A

Screening programme refers well people for further investigation

8
Q

What is a false negative?

A

Failure to refer people who do actually have early disease

9
Q

What is sensitivity?

A

The proportion of the people with the disease who are correctly identified by screening test

Correctly Positive screening test/ (CPST+Negative screening test but has disease)

10
Q

What is the specificity?

A

The proportion of the people without the disease who are test negative

“If I don’t have the disease, will I test negative?”

11
Q

What is positive predictive value?

A

The probability that someone who has tested positive actually has the disease

PPV = True positives / (true + false positives)

12
Q

What is negative predictive value?

A

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

NPV = True negatives / (false + true negatives)

13
Q

What are the advantages and disadvantages for screening for disease?

A

Adv:

  • Early detection may improve outcome
  • True negatives reassure patients

Disadv:

  • False positives expose patients to invasive diagnostic tests
  • False negatives falsely reassure patients
  • False negatives not offered diagnostic testing that could benefit
  • Expensive interventions could divert money away from treatments
14
Q

What is lead time bias??

A
  • Screened patients appear to survive longer, but only because they were diagnosed earlier
  • Patients live the same length of time, but longer knowing they have the disease
15
Q

What is length time bias?

A
  • Screening programmes are better at picking up slow-growing, unthreatening cases than aggressive, fast-growing ones
  • Diseases that are detectable through screening are more likely to have favourable prognosis, and may indeed never have caused a problem
16
Q

What is selection bias?

A
  • Those who have regular screening are also likely to engage in other health behaviours that protect them from disease
  • Similar to ‘healthy worker’ bias
17
Q

Give 3 examples of screening programmes in the Uk

A
  • PKU
  • downs syndrome
  • breast cancer
18
Q

Give 2 sociological critiques of screening

A
  • Surveillance critiques
  • Victim blaming - not all individuals can take responsibility for their own health
19
Q

What is the illness iceberg? Why is it relevant to STIs?

A

Numerb of cases identified vastly outnumbered by unidentified cases

Relevant to STIs as many are asymptomatic or present transient non specific symptoms

20
Q

What is the difference between sensitivity and PPV?

A

100% sensitive is everyone with the disease is picked up

100% PPV is everyone who tests positive has the disease

21
Q

What is the difference between specificity and NPV?

A

100% specific is everyone who doesnt have the disease tests negative

100% NPV is everyone who tests negative doesnt have the disesae