Abstract
This article provides an introductory step-by-step process to appraise an article on diagnosis. The authors introduce these principles using a systematic approach and case-based format. The process of assessing the validity of an article on diagnosis, determining its importance, and applying it to an individual patient is reviewed. The concepts of study population homogeneity, reference and criterion standards, and completeness are discussed to help physicians determine an article's validity. Instruction on calculating prevalence, sensitivity, specificity, and positive and negative predictive values and likelihood ratios is provided and applied to a hypothetical clinical scenario. Study generalizability and the role of patient values, expectations, and concerns are also addressed. The skills learned from appraising an article on diagnosis in the manner outlined provides a solid basis for life-long learning and improved patient care.
Every medical school graduate is taught how to assess and diagnose a patient's condition. A diagnostic test and its results are important tools that help guide physicians to the appropriate diagnosis by revealing the likelihood of whether or not a patient has a specific condition.
1 Results of the best diagnostic tests remove all doubt that a patient has (or does not have) an identifiable disease or disorder. However, not all diagnostic tests are equal in their ability to differentiate the presence, absence, or severity of a particular disease or condition present in a patient. Therefore, clinicians need a method for selecting the best test to meet a particular patient's needs.
2 Evidence-based medicine (EBM), the practice of appraising the literature in a time-efficient manner to answer a clinical question about, and for, the patient,
3 is such a method.
In this article, we present a strategy for busy clinicians, physician residents, and medical students to critically assess the medical literature on diagnosis. In-depth details of research methods are beyond the scope of this introductory series on EBM. Readers are encouraged to seek further training on these topics with supplemental learning opportunities and continuing medical education. Finally, the clinical scenario described has been simplified to provide readers with an illustrative example for the general concepts introduced.
To find an article that is appropriate to review for the purpose of better establishing patient diagnosis, physicians can approach searching the evidence in two ways. In general, physicians who practice EBM search the evidence for an article that contains the information sought. However, physicians in the habit of summarizing articles relevant to their practice can first refer to their clinically-appraised topics (CATs) when faced with a clinical question.
Similar to the index card method of recording researched information, CATs are a personal method of documenting the results of any article in medical literature for a specific clinical problem.
3 These records are simply summaries of a study and its results that a physician can create for later retrieval, review, and reuse (
Figure 1). The most thorough CATs consist of the article title, the clinical “bottom line,” the clinical question, a summary of the results, comments, the date the study was published, and any relevant citations.
3 A more detailed description of these components is available in
Figure 2.
4 Physicians may choose to share their CATs with colleagues, in which case physicians should also include their name or initials as the CAT appraiser.
A CAT is not a systematic review and should not be considered a practice guideline because the information found in it may not be authoritative.
3 However, physicians will begin to refine and improve their EBM skills after summarizing varying clinical issues in this fashion.
3
When searching the evidence for a clinically relevant article on diagnosis, systematic reviews and meta-analyses are the most authoritative types of reports.
3 These studies, which critically appraise and summarize multiple similar studies concerning a common medical problem, are not as numerous as individual articles. However, such reviews are only as good as the individual studies they include. A physician must be vigilant in critically assessing a systematic review or meta-analysis before putting its recommendations into practice. For guidelines on how to appraise such review articles, a handbook is available on The Cochrane Collaboration Web site (
http://www.cochrane.org/resources/handbook/Handbook4.2.6Sep2006.pdf).
In the absence of a systematic review or meta-analysis, individual articles are often the only source of new information available to clinicians. Assessing these individual articles (
Figure 3) is the focus of this paper.
To ascertain the validity of an individual article, physicians need to determine not only if the study's results and conclusions were accurately deduced but also if the methods used to arrive at the conclusions were free of error and bias. This is the most crucial step in evaluating an article. If its validity is questionable, the article's results cannot be confidently interpreted.
2,5,6 Physicians may use the following questions
3 to help them determine an article's validity:
Now that a diagnostic article of interest is found and is deemed to have merit, one can evaluate its results to determine its general usefulness (
Figure 4). Although this step of the appraisal process for articles on diagnosis appears intimidating, it only requires basic mathematic and statistical skills. With practice, these invaluable calculations will become second nature.
For example, a positive result on a rapid streptococcal antigen test rules in (SpPin) the diagnosis of a streptococcal pharyngitis, and a negative D-dimer test result effectively rules out (SnNout) the diagnosis of deep venous thrombosis (
Figure 5).
Now that the article has been reviewed for its validity and relevance to the physician's patient and it is determined to have significant clinical applicability, one still needs to answer a fundamental question: Can these results benefit the patient?
3
If a physician cannot confidently answer “yes,” the article must be placed aside and a new search started. The potential for “wasted time” is the main factor behind why physicians often do not apply this step. However, the real waste of time— not to mention a potential for harm—would result from implementing results that cannot be expected to help the patient or that are unrealistic to apply in the clinical setting.
The shift in pretest probability to the positive predictive value (or posttest probability) for a given diagnostic test is an effective discriminator for choosing between competing tests. Large LR+ values and small LR- values are indicative of significant shifts. For example, a diagnostic test that provides a LR+ or LR- of 1.0 will not shift the posttest probability at all.
1,3 Therefore, it would be wasteful to perform the test because its results would not benefit the patient or the clinical decision-making process. On the other hand, a test with a LR+ of 10.0 would shift a pretest probability of 50% to a positive predictive value of 92%, which would be clinically useful.
1,3
In addition to the test's pre- to posttest shift, one needs to consider the cost and invasiveness of the tests when choosing between competing diagnostic tests. When these competing elements are considered and balanced with the patient's needs and informed consent, physicians can be confident that the best evidence is being applied in the most efficient and effective manner (
Figure 6).
Although most clinicians are already incorporating EBM principles in their practices, often instinctively, some physicians may require a more organized approach to integrating this relatively new model of self-education. Improved comfort levels and true expertise in the practice of EBM are the result of additional education, repetition, and self-assessment. The principles of EBM allow physicians to stay informed while also improving the quality of the information communicated to patients during patient encounters. The systematic approach that is used to appraise an article on diagnosis is but one step in practicing EBM. Remember, the goal is always to provide the best care possible to patients—using one's clinical expertise to address patient values and expectations for treatment.