The principles of population Screening Flashcards
What is screening?
The process of identifying healthy people who are at a higher risk of developing a health problem.
Then testing these indivduals before the onset of symptoms
What is the purpose of screening?
Reduce the risk of future ill health via early treatment
To give information for informed decision making
What is meant by population screening?
Tests a target group in a structured programme.
What type of prevention stratgery is screening?
Secondary
Note primary - stops a disease before it happens
Secondary - identify a disease in an early stage
tertiray - when an event is already happened, prevent it from getting worse or happening again
What is the meaning of a positive or negative screening result?
Positive - increased risk of a disease developing
Negative - decreased risk of a disease developing
*specific to a time and circumstance, results may change at a different date.
What are some of the options after a positive screening test result?
Advice and support
Treatment for condition to slow progression
No further action (if further tests are negative)
Further tests - always happens first regardless of the above options.
What do we need to ensure patients with a negative screening test result understand?
Low risk at this moment of time in these conditions
May still get the disease in the future
Should still check out any unusual symptoms at the doctors
Should return for next screening interval as normal
What do we need to ensure patients with a positive screening test result understand?
Further information and investigations are often needed/recommended
The patient can refuse further tests
This indicates they are at an increased risk having a disease, this is not always a diagnosis with this disease.
What are the different criteria for a screening programme?
Condition - important (effect quality/qunatity of life), well understand, longer latent period, primary prevention or treatment available
Test - simple, safe, acceptable
Intervention - effective
Screening programme - evidence based, benefits outweight costs, properly resourced
What is meant by a latency period and why is it important in public health screening?
Latency period is the time between when a disease is identifiable and when the symptoms start
Diseases with a longer latency period are more likely to be picked up in and benefit from early treatment from a screening test.
How should a test be designed to be acceptable?
Non-invasive (not needing to cut into anyone)
Low ‘eew factor’ patients are often less willing to do a stool sample for example
Patient comfort
Social stigma
e.g around cervical smeer test.
What does sensitivity mean in regards to a screening test?
The probability of testing positive if the disease is truly present
Should have few false negatives
What does specificity mean regarding a screening test?
Probability of testing negative if the disease is truly negative.
Should have few false positives
What is positive predictive value in regards to screening programmes?
PPV - probability of truly having the disease based on a positive test outcome.
What is negative predictive value in regards to public screening test?
The probability of truly being disease negative based on a negative test outcome.
What is important to remember when analysing PPV and NPV statistics?
Values are influenced by community background and time sensitive situations
E.g during peak pandemic when more people had COVID the PPV value was higher as you probably did have covid even without testing.
How do you calculate sensitivity of a screening programme?
True prositives + False negatives
