Screening Flashcards
What is screening?
A process that tests for a condition or disease in a population of apparently well people who are in a high risk population - purpose is PREVENTION
What is primary prevention
Aims to prevent a disease from occuring
What is secondary prevention
Detection of a disease in its early stages in order to alter the course of disease and maximise changes of complete recovery
What is teritary prevention
Trying to slow down the progression of the disease
What is a false positive?
When the result of a test is positive although the person does not actually have the disease
What is a true positive?
When the result of the test s positive and the patient has the disease
What is a false negative?
When the result of the test is negative but the patient actually has the disease
What a true negative?
When the result of a test is negative, and this is correct because the patient does not have the diease
What does the sensitivity of a screening programme measure?
The proportion of people with the disease who are correctly identified by the screening test
true positives/people with the disease
What does the specificity of a screening programme measure?
The proportion of people without the disease who are correctly excluded by the test
true negative/population without the disease
What is the positive predictive value (PPV) of a screening programme measure?
The proportion of people with a positive result who actually have the disease
true positive/positive results
What is the negative predictive value (NPV) of a screening programme measure?
The proportion of people with a negative result who do not have the disease
true negatives/all negatives
What is the result of a screening test with a low sensitivty
Not all patients with the disease will be identified
What are the possible consequences of a screening programme with a low PPV
- patients potentially receive unnecessary diagnostic procedures
- may cause unnecessary anxiety as the test was positive but the patient DO NOT have the disease
- cost
What is prevalence?
The proportion of a population found to have the disease
What is incidence?
The number of new cases within a specified time period, divided by the population at risk
What is the Wilson and Jungner criteria for screening? In terms of -the condition -the treatment -the test -the benefits
THE CONDITION
a) it should be an serious health problem
b) the aetiology should be well undestood
iii there should be a detectable early stage
THE TREATMENT
a) there should be an accepted treatment for the disease
b) facilities for diagnosis and treatment should be available
c) there can’t be an unmanageable extra clinical workload
THE TEST
a) a suitable test should be devised for the early stage
b) the test should be acceptable for the patients
c) intervals for repeating the test should be determined
BENEFITS
a) there should be an agreed policy on whom to treat
b) the cost should be balanced against the benefits
What selection bias?
People who choose to participate in screening programmes may be different from those who do not
What is lead time bias?
Screening merely identifies the disease earlier than before and thus gives the impression that survival is prolonged (but survival time is unchanged)
What is time-length bias?
Diseases that have a longer period of presentation are more likely to be detected by screening than the ones with shorter time of presentation
