Screening Flashcards
What is screening?
A strategy used in a population to identify the possible presence of an as-yet undiagnosed disease in individuals without signs or symptoms. They are designed to sport disease early
What are Junger and Wilson’s criteria for a good screening programme?
Condition should be an important health problem
Should be accepted treatment for disease
Facilities for diagnosis and treatment available
Recognisable latent or early stage
Test should be acceptable to the population
Natural history of the disease should be understood
Agreed policy in who to treat as patients
Cost of case-finding balanced
Case finding is a continual process
What are the disadvantageous of screening?
Can involve cost and use of medical resources on a majority of people who don’t need it
Adverse effects of screening e.g. radiation
Overdiagnosis
Unnecessary investigation of false positive results
A false sense of security from false negative results
In relation to screening programmes, what is overdiagnosis?
Identifying abnormalities that would never cause a problem in a person’s lifetime
In terms of a diagnostic test what is sensitivity?
The true positive rate
100% sensitivity = no false negatives
In terms of a diagnostic test what is specificity?
The true negative rate
100% specificity = no false positives
What screening programmes are offered in Scotland, who are they offered to?
Newborn screening
Diabetic retinopathy screening for those over 12 with diabetes
Cervical screening for women aged 25-65
Pregnancy screening
Breast screening for women aged 50-70
Bowel screening for those aged 50-74
Abdominal aortic aneurysm screening for men aged 65
What are the differences between screening tests and diagnostic tests?
Screening tests are simple, affordable, acceptable and have low risk of complications but merely act as a sieve to find those most at risk of disease
Diagnostic tests are more complex, expensive, have higher risks and are less suitable for testing large groups of people but are the gold standard for diagnosis
A multidisciplinary panel decides whether or not screening programmes should be offered. Which committee oversees this?
UK national screening comittee
What types of bias are particular pitfalls when studying the effectiveness of screening?
Healthy volunteer bias
Lead time bias
Length time bias
What is lead time bias in relation to screening programmes?
Lead time is the length of time between the detection of disease and its usual clinical presentation
Lead time bias is where a screening programme appears to give increased survival time without actual doing so because of lead time
Describe length time bias in terms of cancer screening
Faster growing tumours generally have shorter asymptomatic phases than slower growing tumours thus they have a shorter period of time in which the cancer is present in the body but not yet causing symptoms which they would seek advice about. Thus, slower growing cancers are more likely to be picked up by screening rather than symptoms than faster growing cancers due to the fact that they have a longer asymptomatic phase. These slower growing cancers are likely to have better outcomes anyway and so this can give the impression that detecting cancer through screening causes cancers to be less dangerous when in fact less dangerous cancers are just more likely to be caught by screening
What is the formula for calculating sensitivity?
Sensitivity = number of true positives / ( number of true positives + number of false negatives)
What is the formula for calculating specificity?
Specificity = number of true negatives / ( number of true negatives + number of false positives)
What is the formula for calculating positive predicted value?
Positive predicted value = number of true positives / ( number of true positives + number of false positives)
