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CRITICAL ANALYSIS

DIAGNOSIS



The three main questions to ask yourself about any report before applying its findings to your patients are:

1) Are the results valid?
2) What are the results?
3) Will the patients help me with my individual patient?

The data required to answer these questions varies between the domains and, depending upon the type of question, the types of evidence used.

Were the results valid?

PATIENTS:  There is no sense in testing a diagnostic test on patients who are unlikely to have a condition (If your attending asks you to perform a TVU on a 50-year-old man, you should ask why).  So the first question to ask yourself is whether the patient sample included an appropriate spectrum of patients?  Since you want to test the value of a negative result as well as a positive one, you want to make sure that healthy patients were included.  

BLIND COMPARISON:  You want to compare the test being studied to the reference standard, the recognized preferred test for the condition being tested for.  You want to make sure that BOTH tests were applied independently to ALL patients.  

REPRODUCIBILITY:  Was the test described clearly enough that you could perform it in your setting?  Were the analysis and interpretation of results clearly described?  Otherwise, you can't be sure of the same results.  

What are the results?
As described in the Important Concepts section for diagnosis, the results you'd like to see are the positive and negative Likelihood Ratios.  However, it is far more likely that studies will report Sensitivity and Specificity.  From these, you can compute Likelihood Ratios.  You will also want to know how precise the results of the study using confidence intervals .

Will the results help me in patient care?
In addition to the concerns raised earlier , you will want to be aware of the following issues.

PATIENTS:  Are your patients similar enough that the prevalance of the disease in the study population is similar to that in your patients?  Is the severity of the disease in the test population similar to patients you are likely to see?

BENEFITS:  Are there risks associated with the test?  Are these outweighed by the danger of an undiagnosed disease?

The University of Alberta provides a worksheet for analyzing articles on diagnosis.


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