Block 10

Question 1

What is the intention of a diagnostic test?

Answer 1

To confirm or refute your understanding and belief about diagnosis and/or treatment

Question 2

Define sensitivity

Answer 2

True positive rate =

Number of true positives / number of people with the disease

Question 3

Describe the outcomes of a diagnostic test with high sensitivity

Answer 3

Correctly classifies a high proportion of people who truly have the disease

Question 4

Define specificity

Answer 4

True negative rate =

Number of true negatives / number of people without the disease

Question 5

Describe the outcomes of a diagnostic test with high specificity

Answer 5

Correctly classifies a high proportion of people who truly do not have the disease

Question 6

What is positive predictive value?

Answer 6

The chance a having the disease if your test is positive =

Number of true positives / Number of people who test positive

Question 7

What is negative predictive value?

Answer 7

The chance of not having the disease if the test is negative =
Number of true negatives / Number of people who test negative

Question 8

Which measures of diagnostic tests do not change depending on the population?

Answer 8

Specificity and Sensitivity

Question 9

Which measures of diagnostic tests change depending on the population?

Answer 9

PPV and NPV

Question 10

As prevalence rises… (effect on PPV and NPV)

Answer 10

NPV falls

PPV rises

Question 11

As prevalence falls… (effect on PPV and NPV)

Answer 11

NPV rises

PPV falls

Question 12

The larger the LR+ve…

Answer 12

the greater the chance of having disease if the text is positive

Question 13

The smaller the LR-ve…

Answer 13

the smaller the chance of having disease if your test is negative

Question 14

Define screening

Answer 14

systematic application of a test or inquiry
to individuals at sufficient risk of a specific disorder to warrant further investigation or direct preventative actions
amongst persons who have not sought medical attention on account of symptoms of that disorder

Question 15

What type of prevention is screening (normally)?

Answer 15

Secondary - it aims to prevent disease progression

Question 16

There are 11 national screening programmes, name them…

Answer 16

• AAA
• bowel cancer
• breast
• cervical
• diabetic eye
• fetal anomaly
• infectious diseases in pregnancy
• newborn and infant physical examination
• newborn blood spot
• newborn hearing
• sickle cell and thalassaemia

Question 17

Why carry out screening?

Answer 17

• opportunities for primary prevention are limited
• opportunities for treatment are limited
• screening will give potential for earlier +/- more effective treatment

Question 18

For screening to take place, the condition must:

Answer 18

• be an important health problem
• be adequately understood
• have a detectable risk factor
• have a latent period
• have been targeting by cost-effective primary prevention
• have agreed further management plans in place in the case of a positive test

Question 19

For screening to take place, the test must:

Answer 19

• be simple, safe, precise, and validated
• have a known distribution of test values with a known and suitable cut-off agreed
• acceptable

Question 20

For screening to take place, the treatment must:

Answer 20

• be effective
• have better outcomes if given earlier
• be optimised
• have sufficient policies in place to cover who should be offered it or not

Question 21

For screening to take place, the programme must:

Answer 21

• be confirmed to be effective in an RCT
• acceptable to the professionals and public
• reap benefits that outweighs the harms
• be viable economically in relation to healthcare spending (opportunity cost)
• be well planned; quality assurance, adequate staffing, appropriate facilities

Question 22

Explain length bias

Answer 22

• You are more likely to detect more slowly progressing disease
• Individuals with slowly progressing disease already have a better prognosis than those who present with symptoms/signs
• So if you only look at the disease you have detected by screening then the screening looks as though it’s performing better

Question 23

Explain lead time bias

Answer 23

• Screening makes the length time the patient lives with disease longer because you’ve diagnosed it earlier
• But the patient doesn’t actually live longer - they just have a “lead-time” advantage (like a head start)
• Therefore you shouldn’t measure survival when apprising screening: instead measure deaths prevented

Question 24

What branch of ethics does screening conform to?

Answer 24

Utilitarianism