Secondary Prevention Flashcards
Define screening
Screening is the process of identifying apparently health people who may be at increased risk of a disease or condition. They can then be offered information, further tests and appropriate treatment to reduce their risk and/or any complications arising from the disease or condition.
What 3 categories of things can screening lead to the early detection of?
- disease
- pre-cursor
- susceptibility to disease in individuals with no signs or symptoms
What are 4 methods of screening?
questionnaire
examination
lab tests imaging
imaging
Describe what is meant by:
- false postive
- false negative
False postitive = test result is positive, when person does not have the disease
False negative = test result is negative, when person does have the disease
Describe what is meant by a sensitive test
When is the test more useful?
The threshold is closer to the no disease curve.
This reduces the incidence of false negatives.
The test is more useful when the result is negative as you can be almost certain that the patient does not have the disease.
How is sensitivity calculated from a table?
a/a+c
Vertical!
The number of true positive divided by the total number with the disease
Describe what is meant by a specific test
When is the test more useful?
The threshold for the test is closer to the disease curve.
This reduces the incidence of false positives
This is useful if the test is positive e.g. in down syndrome, as so much rides on a positive test result.
How is specificity calculated from a table?
b/b+d
Vertical!
The number of true negatives divided by the total number with no disease
What is the positive predictive value?
What is the negative predictive value?
How are they calculated?
PPV = if you test positive, how likely is it that you really have the disease
a/a+b HORIZONTAL
NPV = if you test negative, how likely is it that you really don’t have the disease
d/c+d HORIZONTAL
How do you calculate prevalence from the predictive values?
a+c / a+b+c+d
Screening in low risk populations results in high rates of ………. …………. . How does this impact who we screen?
false positives
This is why we only screen high risk populations as oppose to whole populations. To reduce the incidence of false positives, where subsequent diagnosis and treatment could have negative consequences
Describe the relationship between predictive value and prevalence and how this impacts the populations we target.
PPV starts low and increases as prevalence increases.
NPV starts high and then drops off at high prevalence.
NPV remains high for most conditions so still target high risk populations
Differentiate between screening tests and screening programmes.
Screening test is the individual test that says negative or positive. However this is of little use to the patient.
Screening programmes include the test, but consider population at risk, screening interval, options for diagnosis and treatment.
What do screening programmes involve?
- Systematic invitation of an agreed population of apparently healthy individuals to undertake a screening test.
- Further investigation, assessment and diagnosis of those screening positive.
Everyone of the following outcomes has a set of risks. The benefits must outweigh the harm caused by a screening programme.
Explain.
True positive = NNS to benefit, ‘labelling’
True negative = costs and hazards of screening
False positive = costs/hazards of further tests, anxiety, fear of future screening
False negative = false reassurance, disregards symptoms and delays intervention
