Diagnostic Testing and Screening Flashcards
What is a screening test?
A test administered to a group of asymptomatic people to detect signs of a disease. (not diagnostic, it just indicates whether or not someone may have condition)
Test identifies:
Pre-disease abnormality
Early disease
Disease risk markers
What does the WHO define screening as?
Presumptive identification of unrecognised disease or defects by means of tests, examinations or other procedures that can be applied rapidly.
What is the aim of screening for a disease or a risk marker for a disease?
To reduce burden of disease, morbidity from the disease or mortality
What are potential risks of screening?
False negatives
False positives
Over-diagnosis
What should the outcome of screening be?
Screening should do more good than harm
What is diagnostic testing?
Identifies whether a person does or does not have a particular condition.
Research studies compare diagnostic testing to compare accuracy to a reference test or a gold standard.
What kind of testing is idea for diagnostic studies?
Cross-sectional survey prospective with blind comparison to gold standard
How are diagnostic tests conducted?
Researchers give all participants gold standard tests and index tests then the results are compared.
Number of true positives and negatives as well as false positives and negatives are derived and specificity/sensitivity of a test is calculated.
What is sensitivity a measure of?
True positives/all disease positives.
Provides information about how well a test performs in detecting disease in people who have the disease.
What is specificity a measure of?
True negatives/all disease negativites
What are the key questions to ask when appraising the validity (risk of bias) of a diagnostic study?
Was there a clear question for the study to address? (patients in test should include patients with high, medium, and low probability of target disease)
Is the comparison with an appropriate reference standard? (Is standard measure able to provide proof that target disorder is present/not present?)
Did all participants get both tests?
Could the results of the test of interest have been influenced by the results of the reference standard or vice versa? (this can be addressed with a blind study. Results should be decided separately and without knowing the other result)
Was there a clear description of the disease/condition status of the tested population? (Type of patients can affect study results)
Was there sufficient description of the methods for performing the test? (Results should be reproducible and should address the question adequately)
What are the measures for specificity and sensitivity of a diagnostic tool clinically?
Positive Predictive Value (PPV) [probability that a patient has a disease if he or she has a positive test]
Negative Predictive Values (NPV) [Probability that a patient doesn’t have the disease if he/she has a negative test]
What factors are used for determining the utility of a test in predicting the presence or absence of a condition or disease?
The statistics
Positive Predictive Value
Negative Predictive Value
Sensitivity
Specificity
What are the consequences of low sensitivity?
People with disease are missed
False reassurance that people do not have the disease
People might delay seeking treatment
Costs without benefits
What are the consequences of low specificity?
People who do not have the disease believe they do
Unnecessary anxiety
Unnecessary investigative procedures
Costs will increase with no compensating benefits.
