wk 6- diagnostic Flashcards
what is different about a diagnostic question ?
pico
p- considers the patient and also the context. eg, older adults with early signs of cognitive impairment
I- diagnostic test/ index test interested in
c- the reference standard diagnostic test (could be 1 or multiple)
o- the diagnosis of the condition/disease exploring, eg. dementia
hierarchy of diagnostic evidence
level I evidence- systematic review of level II studies
level II evidence- a study of test accuracy with an independent, blinded comparison with a valid reference standard, among consecutive persons with a defined clinical presentation
-compare index test with reference standard, blinded, using consecutive or random samples of patients.
level III- 1 evidence- a level II study but used non-consecutive or non random participants (selection bias)
level III- 2 evidence- comparison with a reference standard that doesn’t meet the criteria of the above 2 evidence
level III- 3 evidence- diagnostic case-control study: the index test results have disease and are compared to the index test results with a healthy group
level IV evidence- study of diagnostic yield (no reference standard): identify participants with the condition of interest by using the index test alone. without a comparator, there is no way to see how accurate the new index test is.
how can you acquire diagnostic studies? 4
-search both the medical index/subject heading AND the term as a keyword
-pubMed clinical queries
-narrow specific search and broad sensitive search
-all academic databases
features of clinical queries in PubMed
There are two key EBM search options:
Search by Clinical Study Category
Find Systematic Reviews
what does search by clinical study category do? and what are the 5 study categories?
searches PubMed for your specified search terms and then applies specialized search “filters” based on research by Haynes, et al. that are dependent on the clinical question you are seeking to answer.
There are five study categories or filters to choose from based on your clinical question:
Etiology: Information addressing causation/harm of disease
Diagnosis: Information addressing disease diagnosis
Prognosis: Information addressing disease prognosis
Clinical prediction guidelines: Data addressing the likelihood of disease presence or absence
Therapy: Information addressing the treatment of disease.
what scope categories are provided for the clinical study category?
Narrow, specific search –> will get more precise, relevant citations but you may miss a number of important studies
Broad: Sensitive search –> includes relevant citations but it is highly likely that you will find some results that are not as relevant.
STARD is?
standards for the reporting of diagnostic accuracy studies
list developed to help with reporting on diagnostic studies
appraisal of diagnostic studies
-interval validity (risk of bias- 6 casp questions)
-results (estimates of diagnostic accuracy)
-if and how it could be applied in clinical context (external validity)
if patients don’t get the diagnostic test and reference standard what could happen?
verification bias.
occurs during investigations of diagnostic test accuracy when there is a difference in testing strategy between groups of individuals, leading to differing ways of verifying the disease of interest.
if blinding is not done what could it result in?
interpretation bias
what are examples of results for diagnostic studies? 3
sensitivity and specificity
post test probabilities of a positive and negative test
likelihood ratios
what is sensitivity?
proportion WITH the disorder (gold standard) who have Positive result (alternative index test)
specificity
proportion WITHOUT the disorder (gold standard) who have a NEGATIVE result (alternative index test)
what does sensitivity / specificity tell us?
results tell us if we should use a test.
specificity and telling if someone has the disorder?????
when a highly specific test is used, a positive test result tends to rule in the disorder
sensitivity and telling if someone has the disordeR???
when a highly sensitive test is used, a negative test result tends to rule out the disorder
what does predictive values tell us?
post test probability, probability of disease given the results of a test.
positive predictive value tells us what?
probability of disease in a patient with a positive (abnormal) test result.
closer to 100% the better the test is at ruling IN disease
negative predictive value tells us?
probability of NOT having the disease when the test result is negative (normal)
closer to 0% the better the test is ruling OUT a disease
if the results are sensitivity 99% and specificity of 95% what does that tell us?
it is a really good test
unless specificity is perfect (100%), falling prevalence leads to false positive results
be aware of prevalence of condition you’re treating
sensitivity and positive predictive value tells us in laymen terms
sens- if a patient has the disorder, what is the chance of getting a positive result on the new test?
ppv- if a patient has a positive result on the new test, what is the chance that they have the disorder?
specificity and negative predictive value in laymen terms
spec- if a patient does not have the disorder, what is the chance of getting a negative result on the new test?
npv- if a patient has a negative result on the new test, what is the chance that they do not have the disorder?
likelihood ratios how are results interpreted?
more useful than predictive values. the results are not influenced by prevalence.
interpreting-
positive likelihood ratio of >2 helps rule IN a disease
positive likelihood ratio of >10 is an extremely good test for ruling IN disease
negative likelihood ratio of <0.5 helps rule OUT a disease
negative likelihood ratio of <0.1 is an extremely good test for ruling OUT disease
cut offs for diagnostic tests???
