Lecture 13 (no 12) - Prevention and Screening Flashcards
What are the strategies for prevention?
- Primary prevention
- Secondary prevention
- Tertiary prevention
What is Primary Prevention?
Prevent the disease from developing
What is Secondary Prevention?
Detect abnormality early and treat it effectively
What is Tertiary Prevention?
Prevent recurrence and maintain quality of life
What is the “high risk” strategy?
- Define threshold of unacceptable risk
- Screen population to define those at high risk
- Intervene to reduce their risk
What is the “mass” strategy?
- Attempt to move whole population to lower risk
- Automatically reduces number at high risk
What is screening?
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
What are some examples of screening?
- Physical examination
- Laboratory test
- Procedure
- History taking
What are the optimal conditions for effective screening?
- Right disease
- Good test
- Effective programme
A suitable target disease for screening should:
- Represent a significant health problem (common / severe)
- Have an effective intervention that improves the outcome of the disease
- Have a well-understood natural history
At what critical point is the ideal time to screen for cancer?
Critical point 2, between early diagnosis and usual clinical diagnosis
The screening test should be:
- Accurate
- Inexpensive
- Safe
- Available/easy to apply to a target population
Which test when positive rules the diagnosis in?
Specific test
SPPIN
Which test when negative rules the diagnosis out?
Sensitive test
SNNOUT
When would you use a highly sensitive test?
- When disease is serious and definitive treatment exist
- When the disease can spread
- When there is minimal cost and risk of subsequent diagnostic evaluations
When would you use a highly specific test?
- When costs or risk of subsequent diagnostic evaluations are substantial
- When false-positive results can harm person physically, emotionally, or financially
How do you deal with excess positive results?
A mechanism is required to weed out false positives (e.g. through further testing)
-Sequential testing VS Simultaneous testing
What makes a screening program the RIGHT program?
- 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
What are the main biases to be avoided in evaluating the benefits of a screening program?
- Volunteer bias
- Lead-time bias
- Length bias
How do you avoid volunteer bias?
- 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
What is Lead-time bias?
The period between the point when disease is detected by screening and when it would have become symptomatic and diagnosed in the usual way
What is Length Bias?
-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)
What are some harms from screening?
- False positives (unnecessary anxiety, work up, treatment costs)
- Inconsequential Disease (excessive treatment, labeling)
- False negatives (increase in risky behavior)
