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ASK
Clinical Question

ACQUIRE
Literature Search

APPRAISE
Evaluate Evidence

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Your Knowledge

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Testing Your Knowledge

Case 4: Diagnosis of Helicobacter pylori infection

This is a self-correcting exercise. Click on Answer for a pop-up box with the response.

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ASSESS
the patient

1. Start with the patient -- a clinical problem or question arises out of the care of the patient

The patient is a middle aged male with symptoms of dyspepsia. Your first concern in managing this patient is to determine if the dyspepsia is related to peptic ulcer disease. This generally requires endoscopy, which is a minimally invasive, but a relatively expensive diagnostic test. To decrease the use of endoscopy, you have been considering the strategy of testing for H. pylori, treating those that are positive, and then doing an endoscopy on those that remain symptomatic.

The standard laboratory ELISA has been the favored screening test for H. pylori but this test can take days to accomplish. Recently you have read about more convenient in-office or "near patient" whole-blood tests (such as FlexSure) that can show results within hours.

Before you consider a change in practice, you want to find out if the these "near patient" tests, such as FlexSure, are as sensitive as the "gold standard" ELISA test for detecting H. pylori.

 

 

ASK
the Question

2. Construct a well-built clinical question derived from the case

Based on this scenario, choose the best, well-built clinical question:

A. How accurate is the Flexsure test and should I use it on my patient?

B.  In adults with suspected H. pylori, are the "near patient" whole-blood tests such as FlexSure, as accurate as the ELISA assay in aiding diagnosis?

C. Can symptoms of dyspepsia and a "near patient", whole-blood test predict H. pylori infection?

ACQUIRE
the Evidence

3. Select the appropriate resource(s) and conduct a search

Based on question C, choose the best search strategy to address the question.

A. Search: h pylori and flexsure Limits English, Clinical Trials

B. Search: dyspepsia AND h pylori AND blood tests

C. Search: h pylori AND (blood tests OR flexsure OR near patient) AND (sensitivity OR specificity)

APPRAISE
the Evidence

4. Appraise the evidence for its validity (closeness to the truth) and its applicability (usefulness in clinical practice)

Read the following article to determine if the article meets the criteria for validity. As stated previously, evaluating the medical literature is a complex undertaking. You will find that the answers to the questions of validity may not always be clearly stated in the article and that you may have to use your own judgment about the importance and significance of each question.

Article: Duggan AE, Elliott, C. Logan RF. Testing for Helicobacter pylori infection: validation and diagnostic yield of a near patient test in primary care.   BMJ. 319(7219):1236-9,1999 Nov 6.

Are the results valid?

1. Independent, Blind Comparison:  Was there an independent "blind" comparison with a reference standard?

2. Spectrum of Patients Studied:  Were patients from an appropriate spectrum for whom the test would be applied in clinical practice?

3. Performance of Reference Standard:  Was the reference standard performed in all cases or did the results of the test being evaluated influence the decision to perform the reference standard?

Are the results of this study valid?

What are the results?

 

Results were available for 375 patients (9 patients had indeterminate ELISA results, 5 had invalid FlexSure results, and 8 had no serum available). 36% of patients had H. pylori infection.

 

H. pylori

ELISA - Positive

H. pylori

ELISA - Negative

 

Totals

FlexSure Positive

90

5

95

FlexSure negative

44

236

280

Sensitivity: measures the proportion of patients with the disease who also test positive for the disease in this study.  Sensitivity = true positive / all disease positives 

90/134 = 67% -- 67% of the patient who had H. pylori infection, tested positive for the disease

Specificity: measures the proportion of patients without the disease who also test negative for the disease in this study.  Specificity = true negative /  all disease negatives 

236/241= 98% -- 98% of the patients who did not have H. pylori, tested negative for the disease.

 

How can I apply the results to patient care?

The in-office or "near patient" test had excellent specificity (98%) but a sensitivity of only 67%, which means that one third of patients infected with H. pylori and a proportionate number of those with peptic ulcer would be missed. The authors conclude that tests with such poor sensitivity should not be used for the test-and-treat strategy.

An alternate approach exists, however. Given its high specificity, the in-office test could be used to rapidly and reliably diagnose two thirds of infected patients; the more sensitive laboratory ELISA could be reserved for those with negative results. However, the cost-effectiveness of this strategy would be highly dependent on the relative costs of the tests (the in-office test would have to be much less expensive than the ELISA) and on the prevalence of H. pylori in the population (the fewer people infected, the larger the number who would need a second test).

All of these factors should be considered before an in-office test is used for the test-and-treat strategy.

Reprinted with permission from the American College of Physicians. (ACP Journal Club 133(1):36, Jul-Aug 2000)


 

APPLY:
talk with patient

5. Return to the patient -- integrate the evidence and clinical expertise, patient preferences and apply it to practice

 

Think about your patient and how best to diagnosis his problem and begin treatment.

Please take a few minutes to give us feedback about this tutorial. Thank you!

 

Revised July 2010