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How does evidence on the diagnostic accuracy of the vertebral artery test influence teaching of the test in a professional physical therapist education program?

Randy R Richter, PT, PhD, is Associate Professor, Department of Physical Therapy, Edward and Margaret Doisy School of Allied Health Professions, Saint Louis University, St Louis, Mo
Mark F Reinking, PT, PhD, SCS, ATC, is Assistant Professor, Department of Physical Therapy, Edward and Margaret Doisy School of Allied Health Professions, Saint Louis University

The purpose of "Evidence in Practice" is to illustrate the literature search process to obtain evidence that can guide clinical decision making. This article is not a case report. The examination, evaluation, and intervention sections are purposely abbreviated.

 

Although faculty members have always had the obligation to remain current in their teaching,¹ they are now being called on to provide evidence to support classroom teaching.² We believe evidence-based teaching leads to several positive outcomes. First, the importance of using evidence to make decisions is modeled to students. Second, students are shown that, for some topics, the evidence is contradictory or sparse. Addressing this ambiguity in the classroom also models ways to address similarly ambiguous clinical situations. Third, evidence-based teaching provides faculty with one standard for deciding what should or should not be included in a curriculum.

When teaching tests and measures to physical therapist students, we believe faculty should teach not only psychomotor competency, but also the appropriate use of test information in the clinical reasoning process. In order to draw confident conclusions from a clinical test, clinicians must understand the diagnostic characteristics of that test. Faculty should present the available evidence on diagnostic accuracy—including sensitivity, specificity, positive and negative predictive values, and likelihood ratios—particularly when the test itself puts the patient at risk. In the case of vertebral artery (VA) testing, the information gained from the test must outweigh the risk to the patient.

Vertebral artery testing is a traditional component of cervical spine examination for the assessment of vertebrobasilar insufficiency (VBI),^3–7 a syndrome of brainstem ischemia.⁸ This syndrome can result from pathologies such as atherosclerosis of the subclavian, vertebral, and basilar arteries; postural hypotension; Stokes-Adams attacks; and mechanical compression from cervical spondylosis.⁹ It also has been attributed to cervical spine examination and intervention techniques, including manipulation^6,10 and passive mobilization.¹⁰ The risk of VBI resulting from cervical manipulation has not been definitively established,¹¹ although Vickers and Zollman¹² report that the risk of adverse events ranges from 1 in 20,000 to 1 in 1 million manipulations. Common symptoms associated with VBI include dizziness, visual changes, slurred speech, difficulty swallowing, lightheadedness, syncope, nausea, or sensory changes.^4,6,10,13 Symptoms of VBI will vary depending on the balance between factors that compromise circulation and compensatory factors such as bilateral circulation and the circulation through the circle of Willis.⁶

Assessment for VBI typically includes questioning the patient about the history of VBI symptoms and performing VA testing, which is believed to compromise the vertebrobasilar system.^3,4,14 The specifics of VA testing regarding patient position, hold times, and sequence of cervical movements vary among authors.^{3,5,7,14–16} A common feature of VA testing, however, involves cervical spine motion to an end-range position of rotation, extension, or combined rotation and extension and then assessing for VBI symptoms. Reproduction of VBI symptoms during the test is considered a positive result and a contraindication for cervical manipulation,^3,4,14 cervical mobilization,^3,5 and end-range rotation.¹⁴ Magee³ describes the VA test as a "clearing" test, which implies that a negative VA test "clears" the patient of VBI and allows cervical mobilization or manipulation to be used, if indicated. We believe this to be a common interpretation of a negative VA test result.

We suggest that there are 2 major issues to consider when using the VA test. First, clinicians use the result of the VA test when making critical intervention decisions. We were concerned, however, that without knowledge of the diagnostic accuracy of the test, clinicians may be making intervention decisions based on incomplete information. Second, some authors indicate that the VA test may actually put patients at risk for VBI.^11,15,17 With this in mind, we posed the question "How does evidence on the diagnostic accuracy of the vertebral artery test influence teaching of the test in a professional physical therapist education program?"

	Database used for initial search:

 
Before we began our search, we knew of one study that described the diagnostic accuracy of VA testing.¹⁸ Because we believed that a successful search strategy would retrieve this study along with other studies reporting on the diagnostic accuracy of the VA test, we used it as a marker for a successful search.

We searched MEDLINE using PubMed, which can be accessed at www.pubmed.gov/. PubMed takes advantage of the MeSH (Medical Subject Heading) vocabulary for indexing bibliographic data in MEDLINE. MeSH terms are assigned to a bibliographic record based on the content of the record. We conducted the search on December 30, 2004.

Initial search:

We started by searching for a MeSH term related specifically to our topic. We used the MeSH database, which can be accessed through a link on the left sidebar of the main PubMed screen and through a dropdown list at the top of the main screen. We entered the term vertebr* into the MeSH database query box. The asterisk is a truncation symbol that instructs PubMed to search for alternative endings. Of the 466 terms that were retrieved, we decided to use the MeSH term Vertebrobasilar Insufficiency, after reading its definition. Because we were interested in studies reporting the diagnostic accuracy of VA testing, we decided to use the Clinical Queries feature available in PubMed. The Clinical Queries feature is accessed from the sidebar on the main screen. The interface of the Clinical Queries feature, previously described by Scalzitti and Sternisha,¹⁹ has changed, and an additional search option (Medical Genetics Searches) has been added (Fig. 1). Scalzitti and Sternisha used the Clinical Queries feature to search for citations of studies examining a treatment effect; because we were asking a diagnostic accuracy question, we used this feature to search for citations of articles related to diagnostic testing.

View larger version (28K): [in this window] [in a new window]   Figure 1. Clinical Queries uses predefined search filters to limit retrieval to records of studies that use a specific method. Source: National Library of Medicine

From the MeSH database screen, we chose sVertebrobasilar Insufficiency and clicked the Links option at the right of the term. A dialog box appeared, offering 3 linking options: PubMed, Clinical Queries, and NLM MeSH Browser. We clicked on Clinical Queries to instruct PubMed to enter the MeSH term into the Clinical Queries screen. We then selected the diagnosis and narrow, specific filters and clicked on Go. We retrieved 23 citations. Using the Limits option, we limited retrieval to English-language studies that used human subjects and included an abstract. We did not limit the search by years. With these limits in place, our search results dropped to 15 citations. After reviewing the titles and abstracts, the only citation to a diagnostic accuracy study of VA testing was Côté et al¹⁸—the article we were using as a marker of a successful search. The other citations described studies of the diagnostic accuracy of imaging techniques such as magnetic resonance angiography, computerized tomography angiography, and transcranial Doppler sonography for cerebral and limb circulation.

At this point, we decided to use the Related Articles link to search for records related to Côté et al.¹⁸ This feature is useful when you know of a study related to your topic and want to determine whether other related studies are in the database. To find related articles, PubMed uses a word-weighting algorithm to compare records. Only the title, abstract, and MeSH headings are compared. Records that are most closely related to the original record are retrieved. Results are displayed from the most to least relevant, with the original record displayed first. When this feature is used, limits are not in effect. Using this option, we retrieved 114 citations. We reviewed the titles and abstracts to determine if the citation referred to an article that examined the effect of cervical motion on VA blood flow and or VBI symptoms. Based on our review of the titles and abstracts, we decided to read 21 articles.^20–40

	Database used for second search:

Top Database used for initial... Database used for second... Database used for third... References

 
Although the 21 articles we planned to review were related to VA blood flow and cervical motion, it was not clear whether they examined diagnostic testing of the VA as performed clinically. Up to this point, the only study of the diagnostic accuracy of VA testing that we had found was the study by Côté et al.¹⁸ Consequently, we decided to search the literature further with Science Citation Index Expanded. A useful feature in Science Citation Index Expanded is the Cited Reference Search (Fig. 2). With this feature we were able to search forward, from 1995 to 2004, for articles that cited Côté Côté et al.¹⁸ We believed that other studies of the diagnostic accuracy of VA testing published after Côté et al¹⁸ would cite this article. The ability to search forward from a given citation is not available in PubMed.

View larger version (47K): [in this window] [in a new window]   Figure 2. The Cited Reference Search feature allows users to search the Science Citation Index Expanded database for records that cite a particular work. Reproduced with permission of Thomson Scientific.

Second search:

We clicked on the Cited Reference Search button (Fig. 2). On the next screen, we entered, in the appropriate query boxes, Cote P for the last name and initial for cited author, J Manip Physiol Ther (the journal abbreviation used by the database publisher) for the cited work, and 1996 for the cited year. We then clicked on Search. The next screen displayed the results of our search including the number of times the article was cited by articles published in journals included in the database (Fig. 2). In our case, Côté et al¹⁸ had been cited 25 times. We limited retrieval of these 25 articles to those published in English and clicked on the Finish Search button to view the references. Next, we printed the titles and abstracts of the 25 records that cited Côté et al.¹⁸ Fifteen of the 25 records in the database were not found when we searched PubMed. Although none of these 15 articles were diagnostic studies of VA testing, we chose to read 2 articles^41,42 that appeared to be commentaries related to VA testing.

	Database used for third search:

Top Database used for initial... Database used for second... Database used for third... References

 
In order to make sure that our search was reasonably comprehensive, our last search for studies of the diagnostic accuracy of tests for vertebrobasilar insufficiency used the CINAHL (Cumulative Index to Nursing and Allied Health Literature) database. We chose CINAHL because we believed that relevant citations might be present that were not in MEDLINE. CINAHL is a smaller database than MEDLINE; however, 55% of the journals in CINAHL are not indexed in MEDLINE.⁴³ For example, a magazine of the Orthopaedic Section of the American Physical Therapy Association, Orthopaedic Physical Therapy Practice, is indexed in CINAHL but is not indexed in MEDLINE. The search was conducted on December 30, 2004.

Third search:

Much of what we had learned from our previous searches we incorporated into the CINAHL search strategy. We combined subject headings (CINAHL's equivalent of MeSH terms) related to VBI ("vertebral artery" and "vertebral artery dissections") and related to diagnostic accuracy ("sensitivity and specificity," "reliability and validity" [which we exploded to capture narrower terms], and "ROC curve"). Our final search string was (vertebral artery OR vertebral artery dissections) AND ([sensitivity and specificity] OR [reliability and validity] OR [ROC curve]). After limiting our results to English we ended with a set of 7 records, which included Côté et al.¹⁸ Of these 7 records, 3 were not in MEDLINE or Science Citation Index Expanded. After reviewing the titles and abstracts, we decided not to read any of the articles because they did not appear to pertain to our question.

Selection of articles for review:

Based on our searches we decided to read a total of 24 articles: 21 articles from PubMed, 2 articles from Science Citation Index Expanded, and the article by Côté et al.¹⁸ After retrieving the articles from our institution's library or through the interlibrary loan department, we found that 2 were letters,^23,24 1 was a reliability study of the validity of Doppler ultrasound velocimetry,³⁹ and 1 examined the effect of head position on blood flow velocity in the internal carotid arteries.⁴⁰ Because these items were not appropriate to our question, they will not be discussed. The remaining 20 studies were classified into 4 groups (Tab. 1).

We retrieved 3 case reports^21,22,36 that described 4 cases involving changes in blood flow with cervical motion and the presence or absence of VBI symptoms. Results from the cases did not consistently support the relationship among cervical motion, blood flow or artery compromise, and VBI signs and symptoms. Two cases were false negatives,^21,36 one case was a false positive,²² and one case was a true positive.²²

The third group included 13 studies that examined the effect of head and neck movements on blood flow in the cerebral vasculature. Six observational studies of people who were apparently healthy individuals described the effect of head position on blood flow, including extracranial VA blood flow,^20,33,37 intracranial VA blood flow,^29,31,38 and blood flow in the internal carotid arteries.³³ Four other observational studies investigated the relationship between cervical motion and VA blood flow in participants who had signs and symptoms that suggested VBI.^25,26,28,30 Three studies used a group design comparing cases with controls to examine the relationship between cervical motion and VA blood flow.^32,34,35 The findings of these studies did not consistently support a relationship among cervical motion, VA blood flow, and VBI signs and symptoms. The lack of consistency in findings may be the result of differences in the characteristics of the participants and in the tools and procedures used to measure blood flow.

Although not a diagnostic accuracy study, 1 of the 13 studies in the third group reported data that we could use to calculate diagnostic accuracy statistics.³⁵ The abstract for this study follows.

Sakaguchi M, Kitagawa K, Hougaku H, Hashimoto H, Nagai Y, Yamagami H, Ohtsuki T, Oku N, Hashikawa K, Matsushita K, Matsumoto M, Hori M. Mechanical compression of the extracranial vertebral artery during neck rotation. Neurology. 2003 Sep 23;61(6):845-7.

Using duplex ultrasonography (US), the authors showed compression of the extracranial vertebral artery (ECVA) during neck rotation in 5.0% of 1,108 patients. Age (per 10-year increase, OR 0.80, 95% CI 0.67 to 0.96), vessel diameters (per 0.5-mm diameter increase, OR 0.63, 95% CI 0.51 to 0.79), and symptoms upon neck rotation (OR 4.01, 95% CI 1.35 to 11.9) were associated with vessel compression. In one case, SPECT revealed decreased cerebral perfusion of the hindbrain during rotation. ECVA US is useful in identifying vessel compression, especially in patients with symptoms on neck rotation.

[© 2003 AAN Enterprises Inc. Abstract reproduced with permission of Lippincott Williams & Wilkins.]

Using duplex Doppler ultrasonography, Sakaguchi et al³⁵ examined blood flow in the vertebral arteries and measured the diameter of the vertebral arteries. Participants included 1,108 people who came to their department for neurovascular evaluation. One hundred thirty-six participants (12.3%) had a history of unexplained vertebrobasilar distribution symptoms. Doppler ultrasound testing was performed on participants with their cervical spine in an extended and rotated position. The position was held for at least 10 seconds. Of the 136 participants with a history of unexplained vertebrobasilar distribution symptoms, 28 had symptoms with ultrasound testing and 108 did not. Of the 28 participants with symptoms during ultrasound testing, 5 had VA compression. Of the remaining 108 participants who had no symptoms during ultrasound testing, 7 had VA compression. Of the 972 participants who had no history of vertebrobasilar distribution symptoms, 42 had VA compression. None of these 972 participants had symptoms with ultrasound testing.

Although Sakaguchi³⁵ did not present diagnostic accuracy statistics, we entered their data into a 2 x 2 table (Tab. 2) and calculated sensitivity, specificity, and likelihood ratios (LRs), along with their 95% confidence intervals (CI). Sensitivity is the proportion of people who actually have the disease and are correctly identified as "positive" by the screening test.⁴⁴ Specificity is the proportion of people who do not have the disease and are correctly identified as "negative" by screening test.⁴⁴ Likelihood ratios combine sensitivity and specificity and indicate the change in odds favoring the disease given the screening test result.⁴⁵ In practice, LRs are used to determine the change from pretest probability to posttest probability of a disorder given a particular test result.⁴⁶ Likelihood ratios are referred to as positive (LR+) when the test results are positive; the greater the LR+, the more likely the condition is present given a positive test result.⁴⁷ Likelihood ratios are referred to as negative (LR–) when the test results are negative; the smaller the LR–, the more likely the condition is absent given a negative test.⁴⁷ An LR of 1.0 does not change the odds for or against the disease.⁴⁵ Jaeschke et al⁴⁸ provide further recommendations for interpreting LRs.

The study by Côté et al¹⁸ was the only study we found that reported diagnostic accuracy statistics for cervical spine movements used in pre-manipulation testing. The abstract for this study follows.

Cote P, Kreitz BG, Cassidy JD, Thiel H. The validity of the extension-rotation test as a clinical screening procedure before neck manipulation: a secondary analysis. J Manipulative Physiol Ther. 1996 Mar-Apr;19(3):159-64.

OBJECTIVE: To determine the validity of the neck extension-rotation test as a clinical screening procedure to detect decreased vertebrobasilar blood flow that might be associated with dizziness. DESIGN: Secondary analysis of a clinical screening test. METHODS: Twelve subjects with dizziness reproduced by the extension-rotation test and 30 healthy control subjects had Doppler ultrasonography examination of their vertebral arteries with the neck extended and rotated. Vascular impedance to blood flow was measured and the presence of signs and symptoms of vertebrobasilar ischemia was recorded. RESULTS: Cutoff points for validity estimates were derived through the percentile and Gaussian methods using impedance to blood flow as the standard. The sensitivity of the extensionrotation test for increased impedance to blood flow was 0%, regardless of the selected cut-off point. The specificity rates for the left vertebral artery were 71% and 67% for the percentile and Gaussian methods, respectively. The extension-rotation test was more specific on the right side, with a rate varying from 90% with the percentile method to 86% with the Gaussian technique. The positive predictive value of the test was 0% and its negative predictive value ranged from 63% to 97%. CONCLUSION: We were unable to demonstrate that the extension-rotation test is a valid clinical screening procedure to detect decreased blood flow in the vertebral artery. The value of this test for screening patients at risk of stroke after cervical manipulation is questionable.

[© 1996 National University of Health Sciences. Abstract reproduced with permission of National University of Health Sciences.]

This study is a secondary analysis of data collected in a previous study by Thiel et al.⁴⁹ We found the study by Thiel et al⁴⁹ after reading Côté et al.¹⁸ We used the study by Thiel et al⁴⁹ to clarify methodological issues reported by Côté et al.¹⁸ Participants were recruited from chiropractic clinics and identified as either experimental (n=12) or control (n=30) subjects. Participants in the experimental group had a history of symptoms related to head and neck movement. In addition, these participants had a positive result on the Wallenberg test (a specific VA test in which the head and neck are held in extension-rotation for 30 seconds); 4 people who had symptoms related to head and neck movement but a negative Wallenberg test were excluded from the study. Radiographic films of the neck and examination by a neurologist were used to rule out nonvascular causes of the symptoms related to head and neck movements. Participants in the control group were healthy; they did not have a history of cardiovascular disease, symptoms related to head and neck movements, or neck pain or stiffness; and they were not pregnant.

The index test for the study was cervical extension-rotation, which was held for at least 30 seconds. The reference test was duplex Doppler ultrasound at C3 to C5. Ultrasound testing was conducted with the subject supine and the head and neck in 3 positions: neutral, head over the edge of the table with the neck fully extended, and head hanging over the edge of the table with the head and neck fully extended and rotated.⁴⁹ Both VAs were examined. The unit of measurement for the ultrasound test was the ratio of systolic peak velocity to end diastolic minimum velocity, which is an estimate of vascular impedance.⁴⁹ A positive index test result occurred when the participant experienced symptoms of vertigo, nausea, tinnitus, light-headedness, visual problems, numbness of the face or one side of the body, nystagmus, vomiting, or loss of consciousness during cervical extension-rotation.

Using data from the control group, Côté et al¹⁸ established 2 cut points to determine whether the ultrasound test was positive. The first cut point was based on the Gaussian (normal) distribution of vascular impedance values and was set at the upper limit of the 95% CI. The second cut point was the 95th percentile of the vascular impedance values. Côté et al¹⁸ calculated sensitivity, specificity, and predictive values for each VA using each cut point, but did not calculate LRs. The reported sensitivity and positive predictive values were 0% for both VAs and for both cut points.¹⁸ Specificity ranged from 67% to 90%, and negative predictive values ranged from 63% to 97%.¹⁸

We used the data from 2 x 2 tables of the diagnostic test results¹⁸ to calculate 95% CIs for sensitivity^# and LRs and their 95% CIs for the neck extension-rotation test. Because there were no true positives for the left and right VAs at each cut point, we added 0.5 to the value of each cell in the 2 x 2 table to permit calculation of LRs and their 95% CIs.⁵⁰ The results from our calculations and values from the data in Côté et al¹⁸ are presented in Table 3. Regardless of the cut point, sensitivity for the extension-rotation test was 0%. The 95% CIs for sensitivity were 0% to 21% for the right VA using the Gaussian method and 0% to 79% for the left VA using the 95th percentile method. Specificity ranged from 67% (95% CI=53%–81%) for the left VA using the Gaussian method to 90% (95% CI=80%–99%) for the right VA using the 95th percentile method. Likelihood ratios and their 95% CIs were calculated using the log method described by Simel et al.⁴⁵ Positive LRs ranged from 0.211 (95% CI=0.014–3.174) for the left VA using the Gaussian method to 0.867 (95% CI=0.054–13.824) for the right VA using the 95th percentile method. Negative LRs ranged from 1.017 (95% CI=0.744–1.392) for the right VA using the 95th percentile method to 1.402 (95% CI=1.030–1.909) for the left VA using the Gaussian method.

Interpretation of the evidence:

After searching PubMed, Science Citation Index Expanded, and CINAHL, we found one study that examined the diagnostic accuracy of VA testing,¹⁸ and we were able to calculate sensitivity, specificity, LRs, and 95% CIs for another study.³⁵ None of the remaining studies examined the diagnostic accuracy of VA testing.

Although Côté et al¹⁸ reported sensitivity, specificity, and predictive values, possible methodological problems limit the usefulness of the findings. For example, in an empirical study on the influence of bias in studies of diagnostic tests, Lijmer et al⁵¹ found that diagnostic accuracy studies using separate groups of participants with and without the disorder (eg, a case-control design) significantly overestimated diagnostic accuracy (relative diagnostic odds ratio=3.0, 95% CI=2.0–4.5) when compared with studies that used consecutive patients. Côté et al¹⁸ used a case-control design. Lijmer et al⁵¹ also found that there was bias in favor of the apparent accuracy of the index test when interpretation of the reference standard was done by people who had knowledge of the results of the index test.

Likewise, in a systematic review of bias in studies of diagnostic accuracy, Whiting et al⁵² found that diagnostic accuracy was biased (sensitivity was increased) when clinical information, such as age, sex, and symptoms, was available during the interpretation of test results. Whether knowledge of clinical history should be available to the person interpreting the index test depends on whether the information would be available in the clinical setting.⁵² In Côté et al,¹⁸ it is not clear if the clinicians who were asking participants about possible symptoms of VBI during the testing were aware of the clinical history of the participant being tested. This knowledge may change how the questions were asked and influence the diagnostic accuracy of the test; that is, participants who were cases may have been questioned more closely than participants who were controls. Finally, Johnson et al⁵³ criticized the method used to measure VA blood flow as reported by Thiel et al,⁴⁹ calling its use as a reference standard into question.

Putting aside the methodological concerns related to the Côté et al¹⁸ study, the sensitivity values reported for the extension-rotation test and the CIs we calculated do not support the use of this test as screening test for VBI. The sensitivity of the test was 0%.¹⁸ The CIs we calculated for the sensitivity were wide (Tab. 3), indicating a lack of precision, which may have been a result of the small number of participants.⁵⁴ In almost all instances, the LRs and their 95% CIs that we calculated (Tab. 3) were close to 1.0, indicating that the extension-rotation test as performed by Côté et al¹⁸ would only slightly change the posttest probability of VBI.^45,48 The exception was the LRs calculated from data using the 95th percentile method as the cut point. In this instance, the upper limits of the positive LRs were large; however, the CI was wide (95% CI=0.073–9.686), indicating a lack of precision and small sample size.⁵⁴ Studies with larger sample sizes could provide more precise estimates of the diagnostic accuracy of the extension-rotation test.

The sensitivity values and 95% CIs that we calculated from the data in the study by Sakaguchi et al³⁵ were larger than those reported by Côté et al¹⁸ (Tab. 3); however, they were still too low for the extension-rotation test to be considered useful as a test to rule out VBI. Likewise, the LR– and 95% CI was close to 1.0. The specificity value and its 95% CI were close to 100% and larger than the specificity values reported by Côté et al¹⁸ (Tab. 3). Such a large specificity value could be interpreted as indicating that the extension-rotation test is useful for ruling in VBI⁵⁵; however, LRs that are calculated from sensitivity and specificity are better indicators of the usefulness of a diagnostic test.^46,56 The LR+ was 4.243 and the 95% CI was 1.678 to 10.729. Positive LRs between 2 and 5 indicate that a positive test result would lead to a small increase from the pretest to posttest probability.⁴⁸ Whether the change would be important would depend on the clinical situation. Although the upper limit of the 95% CI indicates that the extension-rotation test may lead to a large increase from the pretest to posttest probability, the lower limit of the CI indicates that the increase from the pretest to posttest probability would be small and may not be important.⁴⁸ In this case, the data are not definitive.⁵⁷

Teaching decision:

Our teaching decision has a psychomotor component and a cognitive component. We believe that, to gain the psychomotor skill needed to perform the VA test, students can review videos or still pictures of the test maneuver; they do not need to actually perform the test. Two aspects of the VA test led us to this conclusion. First, an individual may be at risk for VBI with the VA test.^{10,11,15,17,42} Second, the VA test using end-range extension-rotation is an uncomplicated movement that does not require advanced psychomotor skills.

Our teaching decision regarding the cognitive aspects of the VA test has 3 components that we believe are crucial in the development of clinical reasoning: (1) interpreting the test result, (2) using VA test results in making intervention decisions, and (3) understanding the strength of the evidence for using the test.

Whether reported by the author¹⁸ or calculated using reported data,^18,35 the sensitivity, LR–, and associated 95% CIs do not support the interpretation of a negative VA test result as a way to rule out VBI. In fact, these data indicate that a negative VA test does not add anything to the clinical decision-making process. The specificity values and LR+ values indicate that a positive VA test may suggest the presence of VBI and require that the clinician consider referring the patient for further diagnostic testing.

As we described earlier, the VA test has been called a clearing test,³ implying that a negative test "clears" the patient of VBI and allows cervical mobilization or manipulation if indicated. The diagnostic accuracy data we found do not support this interpretation. Furthermore, because the VA test does not expose the patient to a high-velocity, low-amplitude thrust, a negative VA test cannot be used to determine the safety of cervical manipulation.^17,42

We believe the strength of the evidence for VA testing is weak. In spite of the common clinical recommendation to use the VA test for VBI,^3–5,14 we found only one study that reported diagnostic accuracy statistics for the VA test.¹⁸ This study appeared to have methodological flaws shown to bias results.^51,52 Many of the studies we reviewed^{20,25,26,28–30,32–35,37,38} indicate that our understanding of the usefulness of VA testing is at an early phase of development.⁵⁸

Sackett and Haynes⁵⁸ describe 4 phases in the development of a diagnostic test. The first phase is supposed to demonstrate that the test results differ between those people known to have the disorder and those who do not. Results from these studies can add insight into the biological basis of the disorder but cannot be used to demonstrate the clinical usefulness of the test.⁵⁸ During the second phase of test development, testing may be done under ideal conditions, comparing people clearly with the disease to those without the disease.⁵⁸ At this time, cut points, which clearly differentiate the groups, can be selected. Because participants known to have or not have the disorder are tested in a phase 2 study, the results cannot be used to infer how the test would perform in a clinical situation.⁵⁸ In the third phase of test development, testing is done under typical clinical conditions.⁵⁸ The pool of participants include people with varying levels of the disorder and people with conditions that could be confused with the disorder of interest. The spectrum of the severity of the disorder should reflect what would be seen in clinical situations where the test will be used.⁵⁸ Studies in the fourth phase are designed to determine whether people who undergo testing have better health outcomes than those who do not undergo testing.⁵⁸

Using these criteria, the Côté et al¹⁸ study represents a phase 2 study. Although not designed as a diagnostic study, we consider Sakaguchi et al³⁵ to represent a phase 2 study as well. Excluding the literature review, commentaries, and case reports, the remaining group studies^{20,25,26,28–34,37,38} represent phase 1 studies at best. We believe that, before the VA test can be used to indicate the presence or absence of VBI, phase 3 studies using consecutive patients in clinical settings and that support the diagnostic accuracy of the test are needed.

The purpose of this article was to examine the diagnostic accuracy of the VA test to inform our teaching of the test. Although we will still teach the VA test to the students, this search has substantially changed how we teach the psychomotor skill and the clinical decisions based on test results. The decision of whether to perform the VA test for a given patient is beyond the scope of this article; however, we believe that any patient seen for cervical conditions should be questioned for symptoms related to VBI. We recognize that diagnostic accuracy data for these questions do not exist; however, they do not put the patient's health at risk. Based on the patient's response to these questions and the clinical judgment of the practitioner, performance of the VA test and referral for diagnostic imaging of VA patency may be appropriate. If the VA test is performed, the practitioner should carefully interpret the results in light of the diagnostic accuracy evidence for the test.

	Footnotes

 
A presentation based on an earlier draft of this paper was given to the Eastern District, Missouri Chapter of the American Physical Therapy Association.

The authors thank Mary Krieger, MLIS, RN, for her informative discussions about PubMed and CINAHL and for her comments on an earlier draft of this manuscript.

Items in brackets are the portions of the MEDLINE record that PubMed will search. In this case, the asterisk instructs PubMed to search for terms with alternate endings such as "diagnosis," "diagnose," or "diagnostic."

Thomson Scientific, 3501 Market St, Philadelphia, PA 19104.

SPECT=single photon emission computerized tomography.

^|| Values were calculated using the software program Confidence Interval Analysis, version 2.1.1, build 48. The program is included with Altman D, Machin D, Bryant T, Gardner M, eds. Statistics With Confidence: Confidence Intervals and Statistical Guidelines. 2nd ed. London, United Kingdom: BMJ Books; 2000. 95% CIs for sensitivity and specificity were calculated using the Wilson method. The log method was used to calculate the 95% CIs for the likelihood ratios.

^# 95% CIs for sensitivity were calculated using the Wilson method available through the software program Confidence Interval Analysis, version 2.1.1, build 48.

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