Preventative Medicine part 2 Flashcards
What are the Criteria for Screening Methods ?
Relative burden of the condition
Feasibility of the screening programme
Potential effectiveness of the programme
Relative burden of the condition ?
When compared to other diseases, the expenses should be justifiable in relation to the available resources. The costs of treating the patients with an advanced outcome should be taken into account.
An outcome that is rare, but serious and easily preventable may be worth screening for.
Example:
Phenylketonuria:
- Congenital disease: inability to metabolize phenylalanine.
- Leads to mental retardation.
- It is easily diagnosed, highly specific and sensitive screening test performed on the blood sample of a new-born.
- Diet low in phenylalanine prevents the outcome.
Measuring effectiveness what are the biases or issues which may contribute to it ?
-Selection bias. Participation differs depending on the outcome or the screening method.
E.g. women with high risk of breast cancer are more willing to attend to a mammography. Those who are at lower risk are less willing to attend .
Lead-time bias. This occurs when a screening identifies the outcome earlier but it does not have any influence on it.
E.g. test A identifies outcome at 55 years, test B at 50, whereas the onset of symptoms starts at 60. Does test A prolong survival for 5 years and test B for 10 years? No. Other outcome measures must be used rather than survival time.
Measuring effectiveness how does the influence of length time Bias ?
Length-time bias. This occurs when there is a longer asymptomatic period.
E.g. slower-growing breast cancer tumours may be detected more likely by screening rather than fast-growing tumours, leading to a better prognosis.
However, slower-growing cancers are less prone to metastasize and therefore the success of the screening method may be over-estimated.
What type of Trial is good for testing outcomes etc ?
A randomized-controlled trial is usually the best method for evaluation. The effects of lead-time, length-time and selection bias are balanced by random allocation.
Advantage of Randomised Controlled Trial
- unbiased distribution of confounders;
blinding more likely;
randomisation facilitates statistical analysis.
Ethical issue - Only real issue
What are the best prevention strategies ?
- Cost-effective
- Targeting high-risk individuals
- Prevention paradox
-
Prevention Strategies for Cost Effective ?
- Those more exposed to the outcome are more willing to do the test.
- It fits society’s perception of the role of medical intervention (i.e. focusing in needy individuals) E.g. screenings to detect STDs (sexually transmitted diseases) should be targeted at those with multiple sexual patterns, practicing unprotected sex, etc. rather than to the general population.
Prevention Strategies for Targeting High risk Individuals ?
Targeting high-risk individuals
Definitions of the high-risk groups should be accurate to avoid anxiety in healthy individuals. -Does not always address the causes of the exposure to a known risk factor. E.g. vaccination of people exposed to cholera without improving the quality of water supply. -It may be considered exclusive. All individuals should have access to interventions aimed at improving their health.
Prevention paradox Prevention Strategies for Prevention Paradox ?
This happens if the high-risk individuals are a small percentage of the whole population at risk.
A large risk-reduction in high-risk individuals does not have an impact on the whole population.
Whereas a slight risk-reduction among many people may have a larger impact on the population.
E.g. 61% of myocardial infarction (MI) occur in men that are not at risk.
If the whole population is aware of the factors influencing MIs (smoking, blood pressure, stress) and modify they behaviour, the benefit would be much more significant.
By using specific strategies -
Benefits of Using different approaches at the same time ?
There are benefits in using different approaches at the same time. E.g. in HIV prevention, health education messages on safer-sex practices are aimed at the whole population.
Whereas, sex-workers and drug-users may be targeted for HIV-screening, and given improved access to condoms and disposable needles respectively.
Should Prostate Cancer be Screened Yes why ?
This is because is one of the biggest killer which occur for men in the UK
12.6% of male cancer deaths in the UK.
- However, it is a disease of older male: 56-70 years old and over at diagnosis. With the risk rising with the ageing population with early detection better to help minimise any effects later in life
Many cases clinically silent .Slient killer therefore the early the
If diagnosed early (no metastasis) – 77% five-year relative survival
With metastasis – 30% five-year relative survival
However, there is a high risk of over-diagnosis with secondary effects: impotence and incontinence.
Prostate
