19.07.08 Screen vs test

Question 1

What is a screen

Answer 1

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

Question 2

Aim of a screen

Answer 2

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

Question 3

Is a screen considered to provide a diagnostic result

Answer 3

No.

Question 4

Who does a screen target

Answer 4

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

Question 5

What do screening individuals need to understand

Answer 5

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

Question 6

Measures of screening performance

Answer 6

Specificity and sensitivity

Question 7

Specificity is

Answer 7

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

Question 8

Sensitivity is

Answer 8

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.

Question 9

Types of screening

Answer 9

Mass, high risk/selective, multiphasic,

Question 10

What is mass screening

Answer 10

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

Question 11

What is high risk/selective screening

Answer 11

Screening of risk populations only.

Question 12

What is multiphasic screening

Answer 12

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.

Question 13

Examples of cancer screening programmes

Answer 13

• 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.

Question 14

Examples of ultrasound screening programmes

Answer 14

• 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)

Question 15

Other screening programs

Answer 15

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

Question 16

Does a test provide a diagnostic result

Answer 16

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

Question 17

What is clinical utility of a test

Answer 17

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

Question 18

What factors determine the utility of a diagnostic test

Answer 18

• 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.

Question 19

Difference between a screen and a test with regard to purpose

Answer 19

• Screening: to detect potential disease indicators

- Diagnostic test: to establish presence/absence of disease

Question 20

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

Answer 20

• 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.

Question 21

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

Answer 21

• Screening: simple, acceptable to patients and staff

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

Question 22

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

Answer 22

• Screening: High sensitivity, to not miss potential disease

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

Question 23

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

Answer 23

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

Question 24

Difference between a screen and a test with regard to cost

Answer 24

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

Question 25

Example of screen vs test for foetal anomaly screening

Answer 25

- Screen: maternal serum screening or ultrasound scan | - diagnostic test: genetic testing (QF_PCR, microarray, etc), physical examination at birth.

Question 26

Example of screen vs test for newborn blood spot screening

Answer 26

- Screen: biochemical analysis for analytes, e.g. IRT | - Diagnostic test: Gene mutation analysis of CFTR.

Question 27

Example of screen vs test for cancer

Answer 27

- Screening: swabs, imaging | - Diagnostic test: biopsy, histopathology, genetic testing

Question 28

Who advises the government on aspects of screening

Answer 28

UK National Screening Committee (UK NSC)

Question 29

What does the UK NSC do

Answer 29

- Reviews policies on screening for various conditions based on new research - Modifying/ implementing/ withdrawing programs.

Question 30

Main criteria for a new screening programme

Answer 30

- Condition - Test - Treatment - Screening programme

Question 31

How does the condition affect development of a screening programme

Answer 31

- 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.

Question 32

How does the test affect development of a screening programme

Answer 32

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

Question 33

How does the test treatment development of a screening programme

Answer 33

- 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.

Question 34

What other criteria should be considered development of a screening programme

Answer 34

- 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.

Question 35

How many screening policies does the UK NSC have

Answer 35

~100

Question 36

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

Answer 36

6-24 months

Question 37

How often does the UK NSC review programmes

Answer 37

Every 3 years.