Contribution of D-dimer plasma measurement and lower-limb venous ultrasound to the diagnosis of pulmonary embolism: a decision analysis model

Diagnostic and therapeutic strategy for acute pulmonary thromboembolism

BACKGROUND

The diagnostic and therapeutic strategy for acute pulmonary thromboembolism (APTE) was published by the Japanese Circulation Society. But in Japan, there has been no report on how to improve the pre-test probability in APTE-suspected cases, to determine a practically available diagnostic strategy, nor has been a report that compares diagnostic methods and therapies for APTE by decision analysis.

METHODS AND RESULTS

APTE was found in 66.7% before using diagnostic imaging techniques. Compared with the absence of APTE, prolonged immobilization, cancer, tachycardia, unilateral leg swelling and inverted T-wave in V(1-3) were found more often in the presence of APTE. The rate of obtaining the result on the day of ordering the examination test was 100% with arterial blood gas analysis, trans-thoracic echocardiography and computed tomography (CT), 78.2% in D-dimer, 85.5% in pulmonary angiography, and 54.5% in perfusion lung scan. Decision analysis showed that the highest expected utility was anticoagulant over 0.51 in pre-test probability, with CT between 0.13 and 0.51.

CONCLUSIONS

The pre-test probability of APTE has already been high before using specific diagnostic imaging techniques in Japan. Our results showed that the diagnostic strategy for APTE made by the Japanese Circulation Society was available in most hospitals in Japan.

Comparison of six D-dimer methods in patients suspected of deep vein thrombosis

We evaluated six D-dimer methods to determine their sensitivity, specificity, and negative predictive values (NPV) in symptomatic patients suspected of deep vein thrombosis (DVT). In patients suspected of DVT a whole blood D-dimer test (SimpliRED, Agen) was performed, and then tested using enzyme-linked immunosorbent assay (VIDAS D-Dimer, BioMerieux; Asserachrome D-Di, Stago International; Dimertest Gold, Agen) and automated immunoturbidometric methods (Advanced D-Dimer, Dade Behring; MiniQuant, Biopool). Each D-dimer method was independently compared with radiographic results to determine sensitivity and NPV. There were 151 patients enrolled in the study. Thirty-five (23.2%) patients had a positive Doppler ultrasound, with 26 proximal, eight distal, and one patient with both proximal and distal thrombus. Two patients (1.3%) had inconclusive studies and were excluded from the analyses. For all patients, the sensitivities for the rapid D-dimer methods were: SimpliRED, 82.3% [95% confidence interval (CI), 80.3-84.3%]; VIDAS D-Dimer, 91.4% (95% CI, 89.9-92.9%); MiniQuant D-Dimer, 96.3% (95% CI, 95.1-97.5%); and Advanced D-Dimer, 97.1% (95% CI, 96.3-97.9%). The sensitivity improved for SimpliRED (86.4%; 95% CI, 83.3-89.4%), VIDAS D-Dimer (95.5%; 95% CI, 85.0-100%), MiniQuant D-Dimer (100%; 95% CI, 96.9-100%) and Advanced D-Dimer (100%; 95% CI, 98.9-100%) in the inpatient population. The automated immunoturbidometric methods, the MiniQuant D-Dimer and Advanced D-Dimer, demonstrated comparable sensitivities and NPV with the VIDAS D-Dimer method in symptomatic patients suspected of DVT, which would suggest that these newer D-dimer methods could be used as part of the diagnostic algorithm for patients suspected of DVT.

Role of fibrin D-dimer testing in emergency medicine

OBJECTIVES

Systemic values of the fibrinolytic plasma marker fibrin D-dimer are raised in a variety of acute clinical conditions. D-dimer values can now be rapidly determined and used to aid diagnosis in emergency medicine. However, despite clinical guidelines, inappropriate and unnecessary measurement of D-dimer values is a significant clinical problem. An understanding of the pathophysiological basis and limitations of the value of D-dimer values may help reduce this problem. This review discusses the pathophysiology of the fibrinolytic system. The currently used assays, clinical indications, and limitations of D-dimer measurement are reviewed. Finally, the potential future clinical indications for measurement of D-dimer values in emergency medicine are discussed.

METHODS

Literature on D-dimer was identified from Medline, along with cross referencing from the reference lists of major articles on the subject

RESULTS

and conclusions: Systemic D-dimer values aids diagnosis, and is potentially a prognostic indicator, in a variety of clinical conditions in emergency medicine. However, it has limited specificity in patients with comorbid conditions. Although, currently, there is no standard D-dimer assay, immunoturbidimetric assays are the most suitable for use in emergency medicine

Nonspecific tests for pulmonary embolism

Many tests have been proposed as useful in the diagnostic evaluation of suspected PE, but nonspecific tests for PE can only add to the level of suspicion one has for the diagnosis. As Anderson indicates, "virtually all clinical and laboratory findings neither diagnose nor exclude the diagnosis of PE. They merely serve to heighten suspicion of the diagnosis and prompt the clinician to pursue additional diagnostic studies." D-dimer measurement is promising as a test to exclude PE in young healthy out-patients, and further study and improvements in technology, can clarify the usefulness of the different methods of performing this assay. For now, diagnostic algorithms for PE should continue to incorporate multiple tests and decision points, but the standard remains specialized imaging techniques.

Detection of pulmonary embolism by D-dimer assay, spiral computed tomography, and magnetic resonance imaging

Pulmonary embolism (PE) remains difficult to diagnose. Ventilation perfusion lung scan, the standard diagnostic test for PE, has poor overall sensitivity. The gold standard examination, pulmonary angiography, is invasive and has some risk, making clinicians reluctant to refer patients. In recent years, new diagnostic modalities have been investigated, including D-Dimer assays, spiral computed tomography (CT), and magnetic resonance imaging (MRI). The authors reviewed the literature and noted that the D-Dimer assays by ELISA or rapid ELISA design are approximately 90% to 95% sensitive, but are not specific for the diagnosis of pulmonary embolism. Spiral CT has been studied with conflicting results; however, in the largest studies the reported sensitivities are greater than approximately 85%. Electron beam CT is an alternative technique, which has not been as extensively studied. MRI is also useful for imaging the pulmonary arterial vasculature, but remains experimental. Although a more accurate assessment of the sensitivity of these new modalities will need to wait until a large angiographically controlled study, such as the planned PIOPED II, can be done, D-Dimer assay and spiral CT are often useful in the detection of pulmonary embolism. The authors make recommendations for their use in a diagnostic algorithm, as alternatives to the standard ventilation perfusion lung scan.

Pulmonary embolism: clinical features and management

Pulmonary embolism (PE) often presents diagnostic difficulties, as its presentation is varied and non-specific. This article attempts a logical approach to the management of a patient with suspected PE, starting with how it may occur, the assessment of clinical probability of PE and subsequent investigations and treatment.

Diagnostic role of ED ultrasound in deep venous thrombosis and pulmonary embolism

Proximal deep venous thrombosis (DVT), which may lead to pulmonary embolism (PE), is one of the serious and underrecognized causes of lower extremity pain and swelling. The diagnosis of DVT requires a confirmatory objective test because clinical signs and symptoms are unreliable. Assessment of thigh vein compressibility with real-time ultrasound is an accurate test for DVT that may be performed rapidly at the bedside. Although unproven, we propose that wider use of this test in the emergency department by emergency physicians might increase the diagnosis of DVT, prevent PE, and reduce utilization of other more costly and invasive diagnostic tests. Evaluation of DVT by compression ultrasound may also be incorporated in the diagnostic workup of suspected PE. In the case of a nondiagnostic ventilation/perfusion scan, demonstration of proximal DVT by ultrasound represents a likely source of PE and an indication for anticoagulation, eliminating the need for pulmonary angiography. In the critically ill patient whose presentation is consistent with massive PE, one rapid approach to the diagnosis may be to combine transthoracic echocardiography with lower extremity ultrasound.

Evaluation of a new, rapid, and quantitative D-Dimer test in patients with suspected pulmonary embolism

Previous studies have suggested the utility of D-Dimer ELISA assays in eliminating a diagnosis of pulmonary embolism (PE). Our objectives were to evaluate the performance of a new, rapid, quantitative, and automated Liatest D-Dimer Assay in patients with suspected PE. Three hundred eighty-six consecutive patients referred to our institution between March 1992 and December 1996 for clinically suspected PE, with recent clinical signs not exceeding 1 wk, were included in this study. Diagnosis of PE was based on clinical evaluation, radionuclide lung imaging, lower limb examination, and, when required, pulmonary angiography. D-Dimer performances, for both Liatest D-Dimer and standard D-Dimer ELISA (Asserachrom DDi), assays, were assessed at the end of the study. Among the 386 patients tested, 146 (37.8%) were classified as PE-positive. Liatest D-Dimer assay had a 100% sensitivity (95% confidence interval, 97 to 100%) and a negative predictive value of 100% (95% confidence interval, 94 to 100%). A normal result, below the cutoff of 500 ng/ml, occurred in 83 of the 386 (21%) patients. There was a strong agreement between Liatest D-Dimer and Asserachrom DDi analyses. These findings suggest that this rapid, quantitative, and automated D-Dimer assay provides a useful diagnostic tool for the clinician with regard to exclusion of PE.

[Role of D-dimers in the diagnosis of thromboembolic disease]

The presence of D-dimers in the bloodstream is secondary to fibrin formation and lysis. Because fibrin is the main component of a thrombus, deep vein thrombosis and/or pulmonary embolism may be excluded with a predictive value of more than 95%, provided D-dimer plasma concentration is below a critical, assay-dependent cutoff. The D-dimer test is thus an ideal screening step in outpatients clinically suspected of venous thromboembolism. Only ELISA tests have been validated in clinical practice at present time for this indication, sensitivity of latex assays being insufficient.

Work-up of patients with malignancy after an intermediate-probability ventilation-perfusion scan: why don't physicians pursue a definitive diagnosis?

RATIONALE AND OBJECTIVES

The authors determined whether there are specific patient characteristics associated with the clinical decision to eschew further diagnostic testing in patients in whom a ventilation-perfusion (V-P) scan indicates intermediate probability of pulmonary embolism (PE).

MATERIALS AND METHODS

The authors reviewed all intermediate-probability V-P scans obtained in a 12-month period. Patients were divided into two groups. Group 1 comprised patients in whom a definitive diagnosis of PE was not obtained and who were not treated for PE (n = 57); group 2 comprised patients in whom the diagnosis of PE was confirmed or excluded and who, if PE was confirmed, received appropriate treatment (n = 14). Age, gender, frequency of malignancy, and survival of patients in groups 1 and 2 were compared.

RESULTS

The frequency of malignancy was significantly greater in group 1 than in group 2 (P = .012). Although the estimated 2-year survival of group 1 patients was significantly less than that of group 2 patients (P = .039), this difference is likely due to confounding by age and malignancy.

CONCLUSION

When an intermediate-probability V-P scan is obtained, physicians are significantly less likely to pursue a definitive diagnosis of PE in patients with malignancy.

Diagnosis of acute lower limb deep venous thrombosis with ultrasound: trends and controversies

Acute deep venous thrombosis of the lower limb is a common and threatening condition whose clinical diagnosis is known to be unreliable. Sonography has gradually superseded venography as the primary diagnostic procedure. A review of the medical literature shows that sonography offers a high level of sensitivity and specificity in symptomatic patients but suffers from a lack of sensitivity at the calf level and in asymptomatic patients. Technologic progress, as well as increased operator experience, may improve sensitivity. Nevertheless, several critical issues remain unresolved, such as the significance of free-floating thrombi, the usefulness of calf and bilateral examination, the criteria that are essential to the diagnosis, the risk of compression sonography, and sonography's role in the direct detection of venous emboli.

Respiratory pearls, pitfalls, and updates

The scope of respiratory and ventilatory support offered in the emergency department (ED) has expanded substantially in the last 10 years. Emergency physicians are now much more aggressive and sophisticated in their management of bronchospasm, pulmonary edema, and acute respiratory failure. New medications and new technologies that have been tested in intensive care units should also be considered appropriate for use in the ED; indeed, from a respiratory support standpoint, the ED should be viewed as an intensive care unit. In this article, the authors outline these new concepts and treatments that allow initiation of "intensive care" in the ED.

Ventilation-perfusion lung scanning and spiral computed tomography of the lungs: competing or complementary modalities?

The recently developed technique of spiral computed tomographic angiography (CTA) is being used for the detection of pulmonary emboli (PE), and several studies have assessed its accuracy using pulmonary angiography as the gold standard. CTA shows a high level of accuracy in the detection of pulmonary emboli in segmental or larger central vessels. The specificity is high enough to eliminate the requirement for angiography if a positive CTA result is found. The main factor limiting the sensitivity of CTA is the frequency of peripheral emboli in the vessels outside the central chest field covered by CTA. The incidence of such peripheral emboli varies in different reports from 0% to 36%, and their significance remains arguable. Interpretative criteria for V./Q.- lung scintigraphy have been refined as a result of the lessons learned from the PIOPED study. Using these modified criteria, and taking into account the prior probability of PE based on the presence or absence of clinical risk factors, treatment decisions can be reasonably made in patients in the following categories: those with normal lung scans, those with high probability scans and high prior probability of PE, and those with low probability scans and low clinical suspicion. Patients with intermediate probability or indeterminate scans, and those in whom the scan results conflict with the clinical expectation, will need further tests. Ultrasound examination of the leg veins, if positive, will select a further subgroup of patients for active treatment. Patients with a negative or inconclusive ultrasound result, who previously have been candidates for pulmonary angiography, can now go on to CTA. The advantages in specificity which CTA offers will make it an important part of the diagnostic workup for selected patients, but in view of its increased cost and high radiation dose compared with V./Q. scintigraphy, the argument that CTA should completely replace lung scintigraphy is currently unsupportable.

Applicability of decision analysis to everyday clinical practice: a controlled feasibility trial

OBJECTIVE

To determine whether decision analysis is applicable to routine management of suspected pulmonary embolism in an emergency care setting.

DESIGN

Controlled feasibility trial.

SETTING

Emergency center of a university hospital.

PATIENTS

Outpatients (n = 84) admitted with clinical and scintigraphic evidence of pulmonary embolism.

INTERVENTIONS

Patients were treated either with the usual clinical work-up for pulmonary embolism (control group) or using a decision analysis model with three options: no action: angiography followed by treatment if positive; treatment without angiography.

RESULTS

All six senior residents in the decision analysis group agreed to fully participate for the 16 months of the study. Summarizing the decision analysis model in a graph was critical to obtain acceptance from all the physicians. Decision analysis (n = 43) and control (n = 41) patients underwent similar numbers of angiographies. However, angiographies for patients who had intermediate clinical probabilities of pulmonary embolism, between 25 and 75%, were more frequent in the decision analysis group (9/13 = 69%) than in the control group (7/20 = 35%). Agreement between clinical probability and lung-scan result was stronger in the decision analysis group.

CONCLUSIONS

Decision analysis was successfully used to manage all patients suspected of having pulmonary embolism admitted to an emergency center during the 16-month trial. There was no insuperable obstacle to acceptance of clinical decision analysis by the physicians. Decision analysis may have resulted in a better discrimination between low and intermediate clinical probabilities of pulmonary embolism.