Latest News - Part 14
Prospective Study of the Diagnostic Accuracy of the Simplify D-dimer Assay for Pulmonary Embolism in Emergency Department Patients: Conclusion
However, this may not occur in real practice. For example, in the present study, although the Canadian score < 2 produced a pretest probability of 2.9%, the actual measured posttest probability of PE was 1.2% (95% CI, 0.8 to 2.0%). In our population, the < 1.0% posttest probability objective was met only when a negative Simplify D-dimer result occurred when the physician’s unstructured pretest probability estimate was < 15%, which yielded a population with only a 2.7% prevalence of PE. With this combination, the actual measured posttest probability of PE was 0.7% (95% CI, 0.3 to 1.4%). We emphasize that these results are from one ED that appears to test for PE at a very low threshold.
Several factors could limit the external validity of this study. The upper limit of the 95% CI for the 0.7% post-test probability for PE after an unstructured estimate of PE < 15% plus a negative Simplify D-dimer result was 1.4%. Patients deemed low risk by clinicians were drawn from a cohort of urban ED patients with an overall 4.7% prevalence of PE. Researchers in Europe have found the prevalence of PE to be > 20% in patients referred from the ED; however, we submit that the threshold at which clinicians decide to order a d-dimer assay to rule out PE in the ED has decreased remarkably in the past 10 years, and continues to drop in the United States and also in Canada.” further
Prospective Study of the Diagnostic Accuracy of the Simplify D-dimer Assay for Pulmonary Embolism in Emergency Department Patients: Discussion
Figure 3 shows the plot of the likelihood ratio as a function of prevalence (R2 = 0.006 with t test on slope yielding p = 0.85; power to detect a significant correlation of 29%). The Pearson correlation coefficient observed for the plot of sensitivity vs prevalence yielded R2 = 0.20, with p = 0.27 from the t test on the slope; the plot of specificity vs prevalence yielded R2 = 0.38 with p = 0.10, and power of 36% (plots not shown). These regression analyses suggest the absence of a significant spectrum bias for either the pretest probability estimate or the underlying prevalence of PE on the diagnostic accuracy of the d-dimer assay. These computations do not address the possibility of spectrum effect, and the power to detect a significant relationship was small for each regression. This large, single-center study measured the diagnostic accuracy of a rapid, point-of-care, qualitative d-dimer assay in the ED setting. In a cohort of 2,302 patients, we found a moderate sensitivity of 80.5% and a relatively high specificity of 72.5%, leading to a negative likelihood ratio of 0.27. review
Prospective Study of the Diagnostic Accuracy of the Simplify D-dimer Assay for Pulmonary Embolism in Emergency Department Patients: Results
The d-dimer assay was performed on 2,302 patients enrolled from October 1, 2001, until June 30, 2004. Clinical characteristics of the study population are shown in Table 1. PE was diagnosed in 108 patients (4.7%; 95% CI, 3.6 to 5.6%). Figure 1 shows the flow diagram of diagnostic imaging relevant to PE. One thousand two hundred sixty-two patients with negative d-dimer results had no imaging performed, so the results of 90-day follow-up served as the criterion standard.
The distributions of pretest probability estimates from the unstructured approach, the Canadian score, and the Charlotte criteria are shown in Figure 2, which demonstrates that patients categorized as low risk for PE, either by the unstructured method < 15%, or by the Canadian score < 2, had a very low observed frequency of PE, at 2.7% (95% CI, 1.9 to 3.6%) and 2.9% (95% CI, 2.2 to 3.9%), respectively. When the Charlotte rule was negative, the frequency of PE was 3.9% (95% CI, 3.1 To 4.8%). read only
Prospective Study of the Diagnostic Accuracy of the Simplify D-dimer Assay for Pulmonary Embolism in Emergency Department Patients: Criterion Standard
Imaging was performed according to a flow diagram posted in the ED. The primary pulmonary vascular imaging study was CT angiography of the chest and venography of the legs, performed and interpreted as we have previously described. Patients who were allergic to iodinated contrast or had a serum creatinine measurement > 1.5 mg/dL underwent ventilation-perfusion scintillation lung scanning, interpreted by board-certified radiologists with specialty training in nuclear medicine in accordance with Prospective Investigation of Pulmonary Embolism Diagnosis study criteria. Lower-extremity venous ultrasound was ordered at the discretion of the attending emergency physician. Radiologists who interpreted images were unaware of the of the d-dimer result. Patients with negative d-dimer results did not necessarily undergo pulmonary vascular imaging. For all patients, the criterion standard was the result of 90-day follow-up, using a structured combination of telephone and medical record follow-up as we have previously described.
Prospective Study of the Diagnostic Accuracy of the Simplify D-dimer Assay for Pulmonary Embolism in Emergency Department Patients: Materials and Methods
Typical indications for the PE rule-out protocol included symptoms of dyspnea, chest pain, or syncope, or physical signs such as a rapid pulse or low pulse oximetry reading that could not be explained by another disease process. Exclusions were hemodynamic instability (clinical signs of shock as described by Jones et al), inability to obtain a blood sample for the d-dimer assay, or patient unwillingness to participate. Prior to diagnostic testing, physicians completed a Web-based electronic data collection form that contained > 70 data fields. The contents and methodology of this Web-based form have been published. The form first asks the clinician to provide his or her own three-tiered, unstructured pretest probability (low, < 15%; moderate, 15 to 40%; high, > 40%), and later parts of the data form contained elements required to compute the Canadian score and the Charlotte rule. The Charlotte rule, when negative, predicts a low-enough pretest probability to allow PE to be ruled out safely using either a quantitative d-dimer or a qualitative d-dimer in conjunction with a normal alveolar dead space measurement. comments
Prospective Study of the Diagnostic Accuracy of the Simplify D-dimer Assay for Pulmonary Embolism in Emergency Department Patients
The ideal screening strategy to exclude pulmonary embolism (PE) in the emergency department (ED) setting would be, fast, cheap, accurate, and easy to use. The d-dimer assay (Simplify D-dimer; Agen Biomedical; Brisbane, Australia) is a single-use, individually packaged immunofiltration cartridge assay. The kits and the reagents can be stored at room temperature. The user adds a drop of whole blood to a well, followed by a few drops of buffer. The test result is read in 10 min at the bedside. The test has an acquisition cost of < $20. However, to ensure patient safety and to maintain a defensible standard of care, any PE screening strategy must have sufficiently high sensitivity and specificity to reliably produce a posttest probability < 1.0%. add comment
Applied Medical Informatics for the Chest Physician: The Challenge of Understanding Clinical Workflow
The root causes for problems with interoperability include changing information technologies, competing proprietary vendor systems, and, simply, the complexity of clinical information systems. More recently, it has been recognized that standardization will be essential to the success of the National Health Information Network. Regional Health Information Networks are now beginning to appear in many states as networks of EMRs. All of this interconnection, though, clearly demands the standardization of systems and communications; in a word, interoperability. more
In the discussion of standards and interoperability, however, has appeared the additional issue of the standardization of language. In the AMI world, this notion of standardized medical terminology usually leads to the term lexicon, or dictionary. There are many examples of standardized medical lexicons (Fig 3). However through the efforts of Dr. David Brailer and the Office of the National Center for Healthcare Information Technology, the lexicon SNOMED has been acquired for use throughout the United States in an effort to catalyze the effective information interchange between information systems. The manufacturers of EMRs are now rapidly incorporating this particular lexicon. It has been said that the complexity of the automation of health care is much like the automation in the aerospace industry. Although the precise complexity grading of health-care automation may never be done, the fact is that there are numerous examples of failed clinical information systems over the past 30+ years that are related in part to the poor understanding and oversimplification of the process of clinical care.