screening Flashcards
what is the phases of the natural history of disease
underlying
susceptible
subclinical
recovery/disability/death
what is primordial prevention
targets the population rather than individuals
focuses on social and environmental intervential
targets conditions that would lead to disease onset
what is primary prevention
targets susceptible populations of individual
prevent a disease from emerging and targets healthy individuals
reduces exposure to risk factors
what is secondary prevention
targets individuals with subclinical disease
early detection
screening programs
what is tertiary prevention
targets clinical and outcome stages of the disease
reduce disease severity and associated complications
what is quaternary prevention
Measures taken to identify patients at risk of over-medicalisation
Targets are patients with illness but no disease
Prevents harmful medical interventions
what are the disadvantages of classification systems
Classification systems are imperfect
Overlap between different types of prevention, and interventions may fall into more than one category
How can smoking cessation fall into primary, secondary and tertiary prevention?
Is all screening secondary prevention, or can some be classified as primary prevention?
what is screening
Screening is the presumptive identification of unrecognized disease or defect by the application of tests, examinations, or other procedures which can be applied rapidly.
what are the principles of screenings
- The condition should be an important health problem.
- There should be an accepted treatment for patients with recognized diseases.
- Facilities for diagnosis and treatment should be available.
- There should be a recognizable latent or early symptomatic phase.
- There should be a suitable test or examination.
- The test should be acceptable to the population.
- The natural history of the condition should be adequately understood.
- There should be an agreed policy on whom to treat as patients.
- The cost of case-finding should be economically balanced
- Case-finding should be a continuous process
what is the purpose of a screening test
detect potential disease indictators
what is the purpose of diagnostic tests
establish presence/absence of disease
what is the target population of screening tests
Large numbers of asymptomatic, but potentially at risk individuals
what is the target population of diagnostic test
Symptomatic individuals to establish diagnosis, or asymptomatic individuals with a positive screening test
what is the test method of screening tests
Simple, acceptable to patients and staff, should not be harmful
what is the test method of diagnostic test
maybe invasive, expensive but justifiable as necessary to establish diagnosis
what is the positive result threshold of a screening test
Generally chosen towards high sensitivity not to miss potential disease
what is the positive result threshold of a diagnostic test
Chosen towards high specificity (true negatives). More weight given to accuracy and precision than to patient acceptability
what is the postive result of a screening test
Essentially indicates suspicion of disease that warrants confirmation
what is the positive result of a diagnostic test
Result provides a definite diagnosis
what is the cost of a screening test
Cheap
what is the cost of a diagnostic test
higher costs
what are the aims of screening
To reduce mortality by early detection and early treatment of a condition
To reduce the incidence of a condition by identifying and treating its precursors
To reduce the severity of a condition by identifying people with the condition and offering effective treatment
To increase choice by identifying conditions or risk factors at an early stage in a life-course when more options are available
what are the screening steps
identify the population eligible for screening
invitation and information
testing
referral of screen positives and reporting of screen-negative results
diagnosis
intervention, treatment and follow-up
reporting of outcomes
what is population-based screening
Systematically screen every person within a population
what is selective screening
Applied to a particular subset of the population, e.g. high-risk group
what is multiphasic screening
more than one test is applied for more than one condition
what is opportunistic screening
during routine healthcare visists
what does the national screening committee do
advises ministers in the 4 UK countries on implementing, continuing and modifying population-based screening programmes
considers all the evidence and makes recommendations based on a set of criteria that have evolved from the Wilson Jungner criteria
what does public health england do
advises on implementation of safe, high quality screening programmes in England
develops standards and provides services that help the localNHSimplement and run screening services consistently across the country
what does UKHSA do
is responsible for planning, preventing and responding to external health threats, and providing intellectual, scientific and operational leadership at national and local level, as well as on the global stage
Is an executive agency sponsored by the Department of Health and Social Care
what is sensitivity
Proportion of true positives that are correctly identified by the test
what is specificity
Proportion of true negatives that are correctly identified by the test
what is accuracy
Proportion of true positives and true negatives that are correctly identified by the test
what is a true positive
when predicted class and true class is positive
what is a false negative
when the predicted class is positive but the true class is negative
what is a false negative
when the predicted class is negative but the true class is positive
what is a true negative
when the predicted class and true class are negative
how do you calculate sensitivity
TP / (TP+FN)
how do you calculate specificity
TN / (FP+TN)
How do you calculate the positive predictive value PPV
TP / (TP+FP) or
How do you calculate the negative predictive value NPV
TN / (FN+TN)
How do you calculate accuracy
(TP+TN) / (TP+FP+FN+TN)
what does a high sensitivity mean
Most people with the condition have been identified
If a test is negative, there is a high degree of certainty that the test subject does not have the disease
If a test is positive, the test subject may or may not have the disease
what does a high specificity mean
Most test subjects with a positive test do have the disease
If the test positive, there is a high degree of certainty that the test subject does have the disease
If the test negative, the test subject may or may not have the disease
what does the PPV tell us
if a test result is positive, what is the probability that the person has the condition?
what does NPV tell us
if a test result is negative, what is the probability that the person does not have the disease?
