Lecture 13 (no 12) - Prevention and Screening

Question 1

What are the strategies for prevention?

Answer 1

• Primary prevention
• Secondary prevention
• Tertiary prevention

Question 2

What is Primary Prevention?

Answer 2

Prevent the disease from developing

Question 3

What is Secondary Prevention?

Answer 3

Detect abnormality early and treat it effectively

Question 4

What is Tertiary Prevention?

Answer 4

Prevent recurrence and maintain quality of life

Question 5

What is the “high risk” strategy?

Answer 5

• Define threshold of unacceptable risk
• Screen population to define those at high risk
• Intervene to reduce their risk

Question 6

What is the “mass” strategy?

Answer 6

• Attempt to move whole population to lower risk

- Automatically reduces number at high risk

Question 7

What is screening?

Answer 7

The investigation of asymptomatic individuals in order to detect those with a high probability of having or developing a given disease

Identification in a population of unrecognized disease (or risk factors) by a “simple” test

Question 8

What are some examples of screening?

Answer 8

• Physical examination
• Laboratory test
• Procedure
• History taking

Question 9

What are the optimal conditions for effective screening?

Answer 9

• Right disease
• Good test
• Effective programme

Question 10

A suitable target disease for screening should:

Answer 10

• Represent a significant health problem (common / severe)
• Have an effective intervention that improves the outcome of the disease
• Have a well-understood natural history

Question 11

At what critical point is the ideal time to screen for cancer?

Answer 11

Critical point 2, between early diagnosis and usual clinical diagnosis

Question 12

The screening test should be:

Answer 12

• Accurate
• Inexpensive
• Safe
• Available/easy to apply to a target population

Question 13

Which test when positive rules the diagnosis in?

Answer 13

Specific test

SPPIN

Question 14

Which test when negative rules the diagnosis out?

Answer 14

Sensitive test

SNNOUT

Question 15

When would you use a highly sensitive test?

Answer 15

• When disease is serious and definitive treatment exist
• When the disease can spread
• When there is minimal cost and risk of subsequent diagnostic evaluations

Question 16

When would you use a highly specific test?

Answer 16

• When costs or risk of subsequent diagnostic evaluations are substantial
• When false-positive results can harm person physically, emotionally, or financially

Question 17

How do you deal with excess positive results?

Answer 17

A mechanism is required to weed out false positives (e.g. through further testing)

-Sequential testing VS Simultaneous testing

Question 18

What makes a screening program the RIGHT program?

Answer 18

• Accessibility of screening service
• Facilities to confirm the diagnosis
• Effective treatment available
• Costs are justified by frequency and severity of the condition
• Established evidence of improved survival and benefits outweigh harms

Question 19

What are the main biases to be avoided in evaluating the benefits of a screening program?

Answer 19

• Volunteer bias
• Lead-time bias
• Length bias

Question 20

How do you avoid volunteer bias?

Answer 20

• Pool all volunteers and randomly assign to screen or not screen
• Important to ensure as many as possible assigned to screening are actually screened
• Follow-up with ppl who showed up and ppl who did not

Question 21

What is Lead-time bias?

Answer 21

The period between the point when disease is detected by screening and when it would have become symptomatic and diagnosed in the usual way

Question 22

What is Length Bias?

Answer 22

-Screening is more likely to detect cases where the disease is progressing slowly, than those where it is progressing quickly
(slow cases are to likely to have favorable outcome therefore, the effect of screening will again appear more favorable)

Question 23

What are some harms from screening?

Answer 23

• False positives (unnecessary anxiety, work up, treatment costs)
• Inconsequential Disease (excessive treatment, labeling)
• False negatives (increase in risky behavior)