How to evaluate diagnostic tests: the Thessaly test

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Date: July-August 2013
Publisher: American Chiropractic Association Inc.
Document Type: Report
Length: 1,887 words
Lexile Measure: 1340L

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A colleague tells you about a new orthopedic test. How do you know if this test is worth integrating into your practice?

You are attending a continuing education seminar and a colleague tells you about a new orthopedic test for evaluating meniscal tears in the knee. The colleague explains that this orthopedic test, called the Thessaly test, is "great" at evaluating meniscal tears and suggests that you begin using it. At this point, you may wonder just how great the Thessaly Test is for diagnosing meniscal tears and whether it is worth incorporating into your physical exam process.

Doctors of chiropractic are commonly faced with challenges when determining a clinical diagnosis, and diagnostic tests are tools used to inform accurate diagnosis. Clinicians are charged with the difficult task of having to navigate an ever changing environment of diagnostic tests; critical appraisal of such tests helps with this process. This article will discuss how to critically appraise studies describing diagnostic tests and will use the example of an article related to the Thessaly test to review this process.

So, where to begin when evaluating diagnostic tests?

Evaluating a diagnostic test requires critically appraising the original article and should focus on 3 primary questions: (1)

1. Are the results valid?

2. What are the results?

3. Can these results help me care for my patient?

Are the results valid?

Assessing the validity of a diagnostic test begins by examining how the study was performed. This information is located in the Methods section of the article. Assessing validity should evaluate how the authors selected the patients and whether a reference standard was used to make comparison with the diagnostic test being studied.

Which patients were included in the study affect the diagnostic test validity. The patients in the study should be representative of a wide spectrum of patients likely to receive the diagnostic test in the real world. It is important that the research study include patients with varying degrees of severity, ranging from mild to severely affected.

The accuracy of a diagnostic test is established by comparing results with a reference or criterion standard, which is occasionally called a gold standard. This reference standard should unequivocally demonstrate the presence of the target condition and should be applied to all patients in the study. Also, the comparisons between the results of the diagnostic test being studied and the reference standard should be blinded. In addition, those individuals making comparisons should be unaware of each test result. This safeguard against bias is commonly referred to as an "independent and blinded comparison." (2)

If the results are valid, proceed to critical appraisal of the results.

What are the results?

Assessing the properties of diagnostic test results requires a dedicated search of the Results section. Diagnostic tests will commonly be reported in terms of sensitivity and specificity.

* Sensitivity is the...

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