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.

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?

The Resource

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

Based on the best, well-built question, choose the best search strategy to address the question. These search examples were done using PubMed in October 2003.

The Evaluation

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

Read the following article, then determine if the article properly addresses the issues of validity. As we 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.

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.

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?

4. Description of Methodology:  Were methods of the test described in sufficient detail to permit replication?

Are the results of this study valid?

This covers the first aspect of evaluating the evidence. There are two additional questions that you, as clinicians, need to consider:

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 status by ELISA
Result of FlexSure test	Positive	Negative	Total
Positive	90	5	95
Negative	44	236	280
Total	134	241	375

Sensitivity (95% CI)	Specificity (95% CI)	+LR	-LR
67% (59 to 75)	98% (95 to 99)	32.4	0.3

Sensitivity: Only 67% of the patient who had H. pylori infection, tested positive for the disease

Specificity: 98% of the patients who did not have H. pylori, tested negative for the disease.

2. Are the Results applicable to your patient?

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)