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Path 19.01 and 19.07 > 19.07.08 Screen vs test > Flashcards

19.07.08 Screen vs test Flashcards

1
Q

What is a screen

A

Process of identifying apparently healthy individuals who may be at increased risk of a disease/condition.

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2
Q

Aim of a screen

A

Early risk identification, thus save lives or improve quality of life. Risk reduction.

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3
Q

Is a screen considered to provide a diagnostic result

A

No.

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4
Q

Who does a screen target

A

Populations. If at-risk individuals are identified, they can then be offered info and further tests/ treatments/ surveillance if appropriate.

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5
Q

What do screening individuals need to understand

A

Screening does not exclude false positives/negatives. It does not guarantee protection.

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6
Q

Measures of screening performance

A

Specificity and sensitivity

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7
Q

Specificity is

A

High specificity means screen has a few false positives as possible. Proportion of those without the condition who return a negative screen result.

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8
Q

Sensitivity is

A

High Sensitivity means the screen captures as many individuals with the condition as possible. Measured as the proportion of those with the condition who have a positive screen result. Detection rate.

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9
Q

Types of screening

A

Mass, high risk/selective, multiphasic,

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10
Q

What is mass screening

A

Screening of a whole population or a subgroup. Offered to all, irrespective of the risk status of the individual.

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11
Q

What is high risk/selective screening

A

Screening of risk populations only.

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12
Q

What is multiphasic screening

A

Application of two or more screening tests to a large population at one time in stead of carrying out separate screening tests for single diseases.

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13
Q

Examples of cancer screening programmes

A
  • Pap smear, to detect potentially precancerous lesions and prevent cervical cancer.
  • Mammography: to detect breast cancer.
  • Colonoscopy and faecal occult blood tests to detect colorectal cancer.
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14
Q

Examples of ultrasound screening programmes

A
  • screening for infectious diseases (Hep B, HIV, syphilis)
  • Inherited conditions (sickle cell, thalassaemia)
  • Down’s, Edwards’, Patau’s syndrome
  • Structural abnormalities (18-21 week scan)
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15
Q

Other screening programs

A
  • Potential sperm bank donors
  • Hearing loss in newborns
  • Newborn screening for serious health conditions (CF)
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16
Q

Does a test provide a diagnostic result

A

Yes, unless inconclusive. Will have clinical utility. Establishes presence/absence of disease.

17
Q

What is clinical utility of a test

A

A test’s capacity to rule a diagnosis in/out and to make a decision possible.

18
Q

What factors determine the utility of a diagnostic test

A
  • Association between results and disease
  • Pre-test probability of a disease
  • demand of test to rule in/out disease with regard to post-test probability.
19
Q

Difference between a screen and a test with regard to purpose

A
  • Screening: to detect potential disease indicators

- Diagnostic test: to establish presence/absence of disease

20
Q

Difference between a screen and a test with regard to target population

A
  • Screening: large numbers of asymptomatic but at-risk individuals.
  • Diagnostic tests: symptomatic individuals to establish a diagnosis or asymptomatic individuals with a positive screening test.
21
Q

Difference between a screen and a test with regard to test method

A
  • Screening: simple, acceptable to patients and staff

- Diagnostic tests: can be invasive, expensive but justifiable to establish a diagnosis

22
Q

Difference between a screen and a test with regard to positive result threshold

A
  • Screening: High sensitivity, to not miss potential disease

- Diagnostic tests: high specificity (true negatives). More weight to accuracy and precision.

23
Q

Difference between a screen and a test with regard to positive result

A
  • Screening: Indicates suspicion of disease, requires confirmation
  • Diagnostic tests: provides a definite diagnosis.
24
Q

Difference between a screen and a test with regard to cost

A
  • Screening: Cheap, large numbers will be tested to identify a small number of potential cases.
  • Diagnostic tests: high costs justified to establish a diagnosis.
25
Q

Example of screen vs test for foetal anomaly screening

A
  • Screen: maternal serum screening or ultrasound scan

- diagnostic test: genetic testing (QF_PCR, microarray, etc), physical examination at birth.

26
Q

Example of screen vs test for newborn blood spot screening

A
  • Screen: biochemical analysis for analytes, e.g. IRT

- Diagnostic test: Gene mutation analysis of CFTR.

27
Q

Example of screen vs test for cancer

A
  • Screening: swabs, imaging

- Diagnostic test: biopsy, histopathology, genetic testing

28
Q

Who advises the government on aspects of screening

A

UK National Screening Committee (UK NSC)

29
Q

What does the UK NSC do

A
  • Reviews policies on screening for various conditions based on new research
  • Modifying/ implementing/ withdrawing programs.
30
Q

Main criteria for a new screening programme

A
  • Condition
  • Test
  • Treatment
  • Screening programme
31
Q

How does the condition affect development of a screening programme

A
  • Is it an important health problem
  • Are there detectable risk factors/ disease markers in early symptomatic stage. Is the epidemiology understood.
  • Is it cost-effective
  • Impact of identifying disease carriers.
32
Q

How does the test affect development of a screening programme

A
  • Simple, safe, precise and validated.
  • Test values should be know, define the cut-offs
  • What further investigations required when a positive result is found
33
Q

How does the test treatment development of a screening programme

A
  • Effective treatments implemented earlier should lead to better outcomes
  • Policies of who should be offered the test.
  • Clinical management should be optimised and standardised across all health providers.
34
Q

What other criteria should be considered development of a screening programme

A
  • Evidence from randomised controlled trials show that programme is effective in the reduction of mortality/morbidity.
  • Is the test socially and ethically acceptable
  • Benefits should outweigh the physical and psychological harm (caused by test/treatment)
  • Value for money
  • Adequate staffing, equipment, facilities available
  • Information available to allow patients to make an informed choice.
  • Justify eligibility criteria, there may be public pressure.
35
Q

How many screening policies does the UK NSC have

A

~100

36
Q

How long does it take the UK NSC to review a screening programme

A

6-24 months

37
Q

How often does the UK NSC review programmes

A

Every 3 years.

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