Principles of screening Flashcards
What is the difference between population screening and diagnostic screening?
- Population screening = a test that is offered to individuals in a target group.. identifying healthy people who may have an increased chance of a disease or condition.
> Screening provider then offers information, further tests and treatment. This is to reduce associated problems or complications - Diagnostic screening = A test used to help figure out what disease or condition a person has based on their signs and symptoms.
What is the criteria for selecting the disease for possible screening?
- The condition:
1- Should be an important health problem
2- The epidemiology, incidence, prevalence and natural history of the condition should be understood
3- All the cost-effective primary prevention interventions should have been implemented as far as practicable.
4- If the carriers of a mutation are identified as a result of screening the natural history of people with this status should be understood, including the psychological implications.
What is the criteria for screening tests?
- The test
1- Should be a simple, safe, precise and validated screening test.
2- The distribution of test values in the target population should be known.
3- The test should be acceptable to the target population.
4- There should be an agreed policy on the further diagnostic investigation of individuals with a positive test result and on the choices available to those individuals.
Screening tests should be : Define
Sensitive
Specific
- Sensitive > Probability of testing positive if the disease is present
- Specificity > Probability of correctly identifying a non-diseased person or true negative.
Define Positive predictive value + Negative predictive value.
- Positive predictive value: Probability that a person actually has the disease given that he or she tests positive
- Negative predictive value: Probability that an individual is truly disease free given that the screening test is negative
What is lead time bias?
- Lead time bias: Early diagnosis falsely appears to prolong survival.
What is length time bias?
- Length time bias: screening over-represents less aggressive disease
> For example: aggressive disease has a short asymptomatic period
> Less aggressive disease has longer asymptomatic period.
What are some limitations of screening programmes?
- Screening tests are not 100% accurate
- Some screening tests can lead to difficult decisions
- Finding out you may have a health problem can cause considerable anxiety
- Normal or negative test normal does not guarantee that you will not go on to develop the condition.
What is the UK NSC criteria for a population screening programme
- Intervention > effective intervention available and intervention at pre-symptomatic phase leads to better outcome
- Screening reduces mortality and morbidity and ethically acceptable
- Benefit of screening must outweigh any harm
- Cost effective
What foetal screening is available?
Women can choose:
not to have screening
to have screening for Down’s (T21) and Edward & Patau’s syndromes(T18 / T13)
to have screening for T21 only
to have screening for T18 / T13 only
What is quality assurance?
- Process of checking that national standards are met (ensuring that screening programmes are safe and effective) and encouraging continuous improvement.
> Public Health England has been responsible for quality assuring the NHS Screening Programmes.
What are the 5 stages of AQ screening pathway?
1- Cohort identification
Identify the eligible group for screening from the population
2- Invitation and information
Invite the full cohort for screening, supplying information tailored appropriately for different groups to enable informed choice to participate
3- Testing
Conduct screening test(s) using agreed/recommended methods
4- Referral
Refer all screen-positive results to appropriate services
5- Diagnosis
Diagnose true cases and identify false positives
6-Intervention/treatment
Intervene/treat cases appropriately
