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Diagnosis critical appraisal guide
Where do I look?
Validity
Are the objectives clearly stated?
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Abstract
Introduction
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Patients and
methods
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Patients and
methods (usually
displayed in
Table 1)
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Methods
Was there an independent, blind comparison between the index test and the ‘gold
standard’?
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Methods
Did the authors have clear objectives when the study began?
Are the analyses and presented results congruent with the original study objectives?
Did the clinicians face diagnostic uncertainty?
Were subjects drawn from a group in which it was not known whether the condition
of interest was present or absent?
Was the test evaluated in a representative spectrum of patients, similar to those
that would be encountered in practice?
Were the full spectrum of cases included – mild to severe, early to late?
Random or consecutive selection will minimise bias.
Was the reference standard test done regardless of the index test results? i.e. Did
the results of the test being evaluated influence the decision to perform the ‘gold
standard’?
Ideally, all study participants should have both the test being studied and the
reference test.
In some situations where the reference test is expensive or invasive, a reasonable
substitute is adequate follow up of those patients with negative index test results to
see whether the diagnosis of interest remains truly absent over time.
The reference standard should be the current ‘best test’ that is closest to ‘truth’.
This may include a combination of tests if that is the current way of determining the
diagnosis.
If you are unsure whether the reference test was the current ‘gold standard’ you
may need to look this up or ask a colleague.
The investigator interpreting the results of each of the tests should be unaware of
the results of the other test, i.e. blinded.
Were the methods for performing the test described in enough detail for the tests
to be replicated?
A reference may be given to another methodology paper.
Faculty of Medicine, Dentistry and Health Sciences
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Methods
References
UWA Medical and Dental Library
What is the accuracy of the test?
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Results
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Discussion
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Methods
How does the test perform in the population being tested (post-test probabilities)?
Are results discussed in relation to the existing knowledge and is the discussion
biased?
The discussion should place results into a clinical context and the authors
conclusions should be justified by the study results.
What level of evidence does this paper give?
Can you assign a Level of Evidence using the Oxford CEBM Levels of Evidence
Hierarchy?
Clinical Importance
Where do I look?
Will patients be better off as a result of the test?
Consider whether patient care will differ for different test results.
Will these changes do more good than harm? Is the target disorder dangerous if left
untreated?
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Abstract
Introduction
Results
Discussion
Acknowledge and understand the risks of the new test.
Are confirmatory tests in patients with false positive index tests risky?
Ask yourself if effective treatment exists for patients with a positive test.
Applicability
Where do I look?
Are the results applicable to your patient or a patient in your care?
Does the test perform differently for different severities of disease?
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Introduction
Discussion
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Introduction
Background
reading
Does the test perform differently for populations with different mixes of competing
conditions?
Will the results change your management strategy?
Think about the test and treatment thresholds for the health condition to be
detected. Will you initiate treatment if this test is positive?
Can you reproduce the test and correctly interpret it in your clinical setting?
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Does the test yield the same result when applied to the same stable patient twice (is •
it reproducible?) Do different observers agree about the test results? Consider
whether inter-observer variability been analysed or addressed.
Results
Discussion
Ask yourself whether you have the same technology and expertise available.
Faculty of Medicine, Dentistry and Health Sciences
UWA Medical and Dental Library
How would I clearly express the results to a colleague or my patient?
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Results
Extract data that helps you describe the study findings to a patient or colleague in
plain English.
Can you perform EBP calculations to help you do this? Try putting the Positive
Predictive Value (PPV) or Negative Predictive Value (NPV) into a sentence for your
patient.
EBP Calculations
Gold standard positive
(condition present)
Gold standard negative
(condition not present)
Test positive
True positive
A
False positive
B
Test negative
False negative
C
True negative
D
Sensitivity = A / (A + C)
Positive predictive value = A / (A + B)
Specificity = D / (B + D)
Negative predictive value = D / (C + D)
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Likelihood ratio for a positive test result = sens/(1-spec)
Likelihood ratio for a negative test result = (1-sens)/spec
Pre-test probability (prevalence) = (A+C)/(A+B+C+D)
Pre-test odds = prevalence/(1-prevalence)
Faculty of Medicine, Dentistry and Health Sciences
UWA Medical and Dental Library