Clinical probability and alveolar dead space measurement for suspected pulmonary embolism in patients with an abnormal D-dimer test result

BACKGROUND: Most patients with suspected pulmonary embolism (PE) have a positive D-dimer test and undergo diagnostic imaging. Additional non-invasive bedside tests are required to reduce the need for further diagnostic tests. OBJECTIVES: We aimed to determine whether a combination of clinical probability assessment and alveolar dead space fraction measurement can confirm or exclude PE in patients with an abnormal D-dimer test. METHODS: We assessed clinical probability of PE and alveolar dead space fraction in 270 consecutive in- and outpatients with suspected PE and positive D-dimer. An alveolar dead space fraction < 0.15 was considered normal. PE was subsequently excluded or confirmed by venous compression ultrasonography, spiral computed tomography and a 3-month follow-up. Radiologists were unaware of the results of clinical probability and capnography. RESULTS: PE was confirmed in 108 patients (40%). Capnography had a sensitivity of 68.5% (95% confidence interval [CI]: 58.9-77.1%) and a specificity of 81.5% (95% CI: 74.6-87.1%) for PE. Forty-five patients (16.6%) had both a low clinical probability and normal capnography (sensitivity: 99.1%, 95% CI: 94.9-100%) and 34 patients (12.6%) had both a high clinical probability and abnormal capnography (specificity: 100%, 95% CI: 97.7-100%). CONCLUSION: Capnography alone does not exclude PE accurately. The combination of clinical probability and capnography accurately excludes or confirms PE and avoids further testing in up to 30% of patients.     

Diagnostic accuracy of magnetic resonance imaging for an acute pulmonary embolism: results of the ‘IRM‐EP’ study

Summary. Background: Magnetic resonance imaging (MRI) has not been validated as an alternative diagnostic test to computed tomography angiography (CTA) in patients with suspicion of a pulmonary embolism (PE). Objectives: To evaluate performance of current MRI technology in diagnosing PE, in reference to a 64‐detector CTA. Patients/methods: Prospective investigation including 300 patients with a suspected PE, referred for CTA after assessment of clinical probability and D‐dimer testing. MRI protocol included unenhanced, perfusion and angiographic sequences. MRI results were interpreted by two independent readers, to evaluate inter‐reader agreement. Sensitivity and specificity were evaluated globally and according to PE location and to clinical probability category. Results: Of 300 enrolled patients, 274 were analyzed and 103 (37.5%) had a PE diagnosed by CTA. For patients with conclusive MRI results (72% for reader 1, 70% for reader 2), sensitivity and specificity were 84.5% (95% confidence interval [CI], 74.9–91.4%) and 99.1% (95% CI, 95.1–100.0%), respectively, for reader 1, and 78.7% (95% CI, 68.2–87.1%) and 100% (95% CI, 96.7–100.0%) for reader 2. After exclusion of inconclusive MRI results for both readers, inter‐reader agreement was excellent (kappa value: 0.93, 95% CI: 0.88–0.99). Sensitivity was better for proximal (97.7–100%) than for segmental (68.0–91.7%) and sub‐segmental (21.4–33.3%) PE (P < 0.0001). Sensitivity was similar for both readers within each clinical probability category. Conclusions: Current MRI technology demonstrates high specificity and high sensitivity for proximal PE, but still limited sensitivity for distal PE and 30% of inconclusive results. Although a positive result can aid in clinical decision making, MRI cannot be used as a stand‐alone test to exclude PE.     

Use of spiral computed tomography contrast angiography and ultrasonography to exclude the diagnosis of pulmonary embolism in the emergency department

Spiral computed tomography (CT) contrast angiography is a promising imaging modality for the diagnosis of pulmonary embolism but the negative predictive value of this test remains controversial. We performed a multi-center prospective cohort study to determine the safety of relying on a negative spiral CT contrast angiography scan to exclude pulmonary embolism. Patients presenting to the Emergency Departments of three tertiary care institutions with clinically suspected pulmonary embolism were potentially eligible for the study. Patients underwent a clinical evaluation to categorize pretest probability into low, moderate, and high categories, and had D-dimer testing performed. Patients at low pretest probability with normal D-dimer were considered to have pulmonary embolism excluded. The remaining patients underwent spiral CT contrast angiography scan of the pulmonary arterial circulation and bilateral venous ultrasound of the proximal leg veins. Patients who were confirmed to have pulmonary embolism or deep vein thrombosis were treated with anticoagulant therapy. Patients in whom the diagnosis of pulmonary embolism was excluded did not receive anticoagulant therapy and were followed for a 3-month period for the development of venous thromboembolic complications. Eight hundred fifty-eight (858) patients were enrolled in this study. Three-hundred sixty-nine (369) patients had low pretest probability and negative D-dimer results and no further diagnostic tests were performed. None of these patients subsequently developed venous thromboembolic complications (0%, 95% confidence interval [CI] 0% to 1.0%). The remaining 489 were referred for spiral CT contrast angiography scan and ultrasound. Sixty-seven patients were confirmed to have pulmonary embolism and an additional 15 patients with negative CT scans had proximal deep vein thrombosis (DVT) on ultrasound for a total prevalence of venous thromboembolism of 82/489 (16.8%). Two of 409 patients who had pulmonary embolism excluded in the initial evaluation phase developed proximal venous thromboembolism (0.5%; 95% CI 0% to 1.8%) in the 3-month follow-up period. These findings suggest that the combination of a negative spiral CT contrast angiography scan and normal venous ultrasound imaging safely excludes the diagnosis of pulmonary embolism in the Emergency Department setting.     

肺通气?蛐灌注显像与螺旋CT血管成像用于肺栓塞诊断的比较研究

目的:比较通气?蛐灌注(V-P)显像和螺旋CT血管成像(SCTA)对肺栓塞(PE)诊断的临床价值。资料和方法:65例疑有PE的患者同时进行了V-P显像和SCTA检查,包括29例PE和36例非PE患者。以最终临床诊断为标准,分别评价两种显像对PE诊断的临床价值。结果:V-P显像对PE诊断的灵敏度、特异性和准确性分别为86.2%,72.2%和78.5%,SCTA分别为79.3%,91.7%和86.2%。非确定性诊断在V-P显像中占受检病例的16.9%,SCTA占4.6%。V-P显像的非确定性诊断多出现于既往有其它心肺疾患的患者,如将非确定性诊断病例去除,则V-P显像的各项诊断参数均较SCTA呈增高趋势。联合应用两种检查法,则诊断的灵敏度、特异性和准确性分别可提高到93.1%,94.4%和93.8%。结论:总体上SCTA对PE诊断的准确性优于V-P显像,应作为首选检查法;如果对受检病例作适当的选择,V-P显像的诊断价值仍有可能进一步提高;联合应用两种显像是目前最为理想的PE诊断方法。     

螺旋CT血管造影在肺栓塞诊断中的价值

目的:讨论肺栓塞的CT征象及螺旋CT三维重建对肺栓塞（PE）的诊断价值。方法：对7例肺栓塞病人进行螺旋CT血管造影检查确定肺栓塞的形态，部位和数目。结果：7例患共累及55处肺动脉极其分支，其CT表现部分充盈缺损，其在垂直面上表现为圆形充盈缺损，在水平面上呈轨道状充盈缺损；完全性堵塞或中断；环状狭窄。结论：螺旋CT血管造影对肺栓塞诊断有极高价值。     

Sensitivity and specificity of the semiquantitative latex agglutination D-dimer assay for the diagnosis of acute pulmonary embolism as defined by computed tomographic angiography

OBJECTIVE: To determine the sensitivity and specificity of the semiquantitative latex agglutination plasma fibrin D-dimer assay for the diagnosis of acute pulmonary embolism by using computed tomographic (CT) angiography as the diagnostic reference standard. PATIENTS AND METHODS: From January 1, 1998, to June 26, 2000, patients who had both semiquantitative latex agglutination plasma fibrin D-dimer testing and CT angiography for suspected acute pulmonary embolism were selected for the study. A D-dimer value greater than 250 ng/mL was considered positive for thromboembolic disease. Diagnosis of acute pulmonary embolism was based solely on the interpretation of the CT angiogram. The D-dimer assay results were then compared with the CT angiographic diagnoses. RESULTS: Of 946 CT studies, 172 (18%) were positive for acute pulmonary embolism. The D-dimer assay was positive for 612 (65%) of the 946 patients. For acute pulmonary embolism, the D-dimer assay had a sensitivity of 0.83 (95% confidence interval [CI], 0.76-0.88), a specificity of 039 (95% CI, 036-0.43), a negative likelihood ratio of 0.44 (95 % CI, 032-0.62), and a negative predictive value of 0.91 (95% CI, 0.87-0.94). CONCLUSIONS: The semiquantitative latex agglutination plasma fibrin D-dimer assay had moderate sensitivity and low specificity for the diagnosis of acute pulmonary embolism. When used alone, the results of this test were insufficient to exclude this serious and potentially fatal disorder. Approximately two thirds of our patients had positive D-dimer assays and required further evaluation to exclude acute pulmonary embolism.     

Subsegmental pulmonary embolism diagnosed by computed tomography: incidence and clinical implications. A systematic review and meta‐analysis of the management outcome studies

Summary. Background: Multiple‐detectors computed tomographic pulmonary angiography (CTPA) has a higher sensitivity for pulmonary embolism (PE) within the subsegmental pulmonary arteries as compared with single‐detector CTPA. Multiple‐detectors CTPA might increase the rate of subsegmental PE diagnosis. The clinical significance of subsegmental PE is unknown. We sought to summarize the proportion of subsegmental PE diagnosed with single‐ and multiple‐detectors CTPA and assess the safety of diagnostic strategies based on single‐ or multiple‐detectors CTPA to exclude PE. Patients and methods: A systematic literature search strategy was conducted using MEDLINE, EMBASE and the Cochrane Register of Controlled Trials. We selected 22 articles (20 prospective cohort studies and two randomized controlled trials) that included patients with suspected PE who underwent a CTPA and reported the rate of subsegmental PE. Two reviewers independently extracted data onto standardized forms. Results: The rate of subsegmental PE diagnosis was 4.7% [95% confidence interval (CI): 2.5–7.6] and 9.4 (95% CI: 5.5–14.2) in patients that underwent a single‐ and multiple‐detectors CTPA, respectively. The 3‐month thromboembolic risks in patients with suspected PE and who were left untreated based on a diagnostic algorithm including a negative CTPA was 0.9% (95% CI: 0.4–1.4) and 1.1% (95% CI: 0.7–1.4) for single‐ and multiple‐detectors CTPA, respectively. Conclusion: Multiple‐detectors CTPA seems to increase the proportion of patients diagnosed with subsegmental PE without lowering the 3‐month risk of thromboembolism suggesting that subsegmental PE may not be clinically relevant.     

D-Dimer test in cancer patients with suspected acute pulmonary embolism

BACKGROUND: The safety of a D-dimer (DD) measurement in cancer patients with clinically suspected pulmonary embolism (PE) is unclear. OBJECTIVES: The aim of this study was to assess the accuracy of the DD test in consecutive patients with clinically suspected PE with and without cancer. METHODS: The diagnostic accuracy of DD (Tinaquant D-dimer) was first retrospectively assessed in an unselected group of patients referred for suspected PE (n = 350). Subsequently, the predictive value of the DD was validated in a group of consecutive inpatients and outpatients with clinically suspected PE prospectively enrolled in a management study (n = 519). The results of the DD test in cancer patients were assessed according to the final diagnosis of PE and the 3-month clinical follow-up. RESULTS: In the first study group, DD showed a sensitivity and a negative predictive value (NPV) of 100% and 100% in patients with cancer and 97% and 98% in those without malignancy, respectively. In the validation cohort, the sensitivity and NPV of DD were both 100% (95% CI 82%-100% and 72%-100%, respectively), whereas in patients without malignancy, the corresponding estimates were 93% (95% CI 87%-98%) and 97% (95% CI, 95%-99%), respectively. The specificity of DD was low in patients with (21%) and without cancer (53%). CONCLUSIONS: A negative DD result safely excludes the diagnosis of PE in patients with cancer. Because of the low specificity, when testing 100 patients with suspected PE, a normal DD concentration safely excludes PE in 15 patients with cancer and in 43 patients without cancer.     

The correlation between elevated cardiac troponin I and pulmonary artery obstruction index in ED patients with pulmonary embolism

Objectives

The aim of this study is to investigate the correlation between cardiac troponin I (cTnI) values and the pulmonary artery obstruction index assessed with spiral computed tomography (CT) scan in emergency department (ED) patients with pulmonary embolism (PE).

Methods

This is a retrospective cohort study of all 179 ED patients diagnosed with PE between December 2004 and January 2007. Study population consisted of 104 (58.1%) of 179 patients with PE in whom both cTnI was measured and a contemporaneously performed CT scan was available for review. In these patients, the levels of cTnI measured in the ED were correlated with the degree of pulmonary vascular obstruction determined by applying the modified Computed Tomography Obstruction Index to the spiral CT scan performed in the ED.

Results

Troponin values were elevated in 20 (19.2%) of 104 patients (95% confidence interval [CI], 11.6-26.8) with a mean cTnI concentration of 0.38 ± 0.44 μg/L. Elevated cTnI value had a significant correlation with main pulmonary arteries involvement using the modified Computed Tomography Obstruction Index score (P = .0001). Elevated ED cTnI value had 53.8% (95% CI, 37.6-66) sensitivity and 92.3% (95% CI, 87-96.4) specificity, 70% (95% CI, 49-86) PPV, and 85.7% (95% CI, 80.7-90) NPV for predicting main pulmonary artery obstruction on CT. Increased cTnI values were highly correlated to intensive care unit admission of patients with PE (RR, 12.83; 95% CI, 3.87-42.4).

Conclusions

Measuring cTnI value might be considered in ED patients who are suspected of having PE. Elevated cTnI should raise the clinician's concern for the possibility of central pulmonary vascular obstruction.     

急性肺血栓栓塞的多排螺旋CT诊断

目的探讨多排螺旋CT对急性肺血栓栓塞(PE)的诊断价值.方法对临床怀疑急性PE的21例患者采用多排螺旋CT行薄层肺动脉造影(CTPA)及间接法深静脉造影(CTV).结果 CTPA检出12例急性PE,间接法CTV检出深静脉血栓8例.1 mm有效层厚图像对段、亚段肺动脉及其内血栓的显示高于3 mm有效层厚图像(P<0.05).结论多排螺旋CT能促进急性PE的诊断.     

An Emergency Department Guideline for the Diagnosis of Pulmonary Embolism: An Outcome Study

OBJECTIVE: To assess the clinical outcome of patients suspected of pulmonary embolism (PE) following implementation of an emergency department (ED) diagnostic guideline. METHODS: A prospective observational study of all patients suspected of PE who presented to the ED during a four-month study period. The authors' modification of the Charlotte criteria recommended D-dimer testing in those younger than 70 years of age with a low clinical suspicion of PE and no unexplained hypoxemia, unilateral leg swelling, recent surgery, hemoptysis, pregnancy, or prolonged duration of symptoms. The primary outcome was the identification of venous thromboembolism during a three-month follow-up period. The negative predictive value of the overall diagnostic strategy and the test characteristics of D-dimer were calculated. RESULTS: A total of 1,207 consecutive patients were evaluated for suspected PE; 71 (5.8%) were diagnosed with venous thromboembolism. One missed case of PE was identified on follow-up, yielding a negative predictive value of 99.9% (95% confidence interval [CI] = 99.5% to 100%). The missed case was a patient who presented with pleuritic chest pain and shortness of breath; a chest radiograph revealed pneumothorax, and the physician decided not to pursue the positive D-dimer result. The patient returned six weeks later with PE. Subgroup analysis of patients having D-dimer performed (n = 677) yields a sensitivity of 0.93 (95% CI = 0.77 to 0.98) and a specificity of 0.74 (95% CI = 0.70 to 0.77). CONCLUSIONS: Implementation of a PE diagnostic guideline in a community ED setting is safe and has improved the specificity of the enzyme-linked immunosorbent assay D-dimer test when compared with previous studies.     

Accuracy of clinical decision rule, D-dimer and spiral computed tomography in patients with malignancy, previous venous thromboembolism, COPD or heart failure and in older patients with suspected pulmonary embolism

BACKGROUND: The diagnostic work-up of patients with suspected pulmonary embolism (PE) has been optimized and simplified by the use of clinical decision rules (CDR), D-dimer (DD) testing and spiral computed tomography (s-CT). Whether this strategy is equally safe and efficient in specific subgroups of patients is evaluated in this study. METHODS: A diagnostic strategy including a CDR, DD test and s-CT was evaluated in patients with malignancy, previous venous thromboembolism (VTE), chronic obstructive pulmonary disease or heart failure and in older patients. PE was ruled out by either an unlikely CDR and a normal DD or a s-CT negative for PE. The safety of these tests was assessed by the 3-month incidence rate of symptomatic VTE in those without PE at baseline. The efficiency was evaluated by calculating the numbers needed to test for the different subgroups. RESULTS: The venous thromboembolic incidence rate after the combination of an unlikely CDR and a normal DD varied from 0% (95% CI: 0-7.9%) in the 482 patients older than 75 years of age to 2% (95% CI: 0.05-10.9%) in the 474 patients with a malignancy. For s-CT these incidences varied from 0.3% to 1.8%. The number needed to test in order to rule out one patient from PE with the studied strategy was highest in cancer patients and in the elderly patients (approximately 10). CONCLUSION: It appears to be safe to rule out PE by either the combination of an unlikely CDR and a normal DD or by a negative s-CT in various subgroups of patients with suspected PE. However, the clinical usefulness of the CDR in combination with the DD as the initial step in the diagnostic process varied among these patient groups.     

64层螺旋CT肺动脉造影在肺栓塞诊断中的应用

目的 利用64层螺旋CT肺动脉造影探讨肺动脉栓塞(pulmonary embolism,PE)的影像表现及其临床应用.方法 对18例Wells评分在2分以上,且临床疑诊为PE的患者,使用64层螺旋CT肺动脉造影检查,进行多平面重建(MPR)、最大密度投影(MIP)和容积再现(VR)后外理.结果 18例均确诊为PE.PE的直接征象:18例患者均见肺动脉腔内充盈缺损改变.1)中央性充盈缺损,呈双轨征和靶征3例;2)偏侧性充盈缺损9例;3)附壁性充盈缺损3例;4)完全性阻塞3例.部分患者可见PE的间接征象:1)肺梗死4例;2)支气管动脉扩张3例;3)胸腔积液10例;4)右室功能不全1例.结论 64层螺旋CT具有快速、准确、无创伤等优点,能清晰显示PE的直接征象和间接征象,是临床明确PE诊断及评价疗效的首选方法.     

Safety of ruling out acute pulmonary embolism by normal computed tomography pulmonary angiography in patients with an indication for computed tomography: systematic review and meta-analysis

Introduction : Several outcome studies have ruled out acute pulmonary embolism (PE) by normal computed tomography pulmonary angiography (CTPA). We performed a meta-analysis in order to determine the safety of this strategy in a specific group of patients with a strict indication for CTPA, that is, 'likely' or 'high' clinical probability for PE, an elevated D-dimer concentration, or both. Methods : Studies that ruled out PE by normal CTPA, with or without subsequent normal bilateral compression ultrasonography (CUS), in patients with a strict indication for CTPA, were searched for in Medline, EMBASE, Web of Science and the Cochrane dataset. The primary endpoint was the occurrence of (fatal) venous thromboembolism (VTE) in a 3-month follow-up period. Results : Three studies were identified that excluded PE by CTPA alone (2020 patients), and three studies that performed additional CUS of the legs after normal CTPA (1069 patients). The pooled incidence of VTE at 3 months was 1.2% [95% confidence interval (CI) 0.8–1.8] based on a normal CTPA result as a sole test, and 1.1% (95% CI 0.6–2.0) based on normal CTPA and negative CUS findings, resulting in negative predictive values of 98.8% (95% CI 98.2–99.2) and 98.9% (95% CI 98.0–99.4), respectively. This compares favorably with the VTE failure rate after normal pulmonary angiography (1.7%, 95% CI 1.0–2.7). The risk of fatal PE did not differ between the diagnostic strategies (0.6% vs. 0.5%). Conclusion : A normal CTPA result alone can safely exclude PE in all patients in whom CTPA is required to rule out this disease. There is no need for additional ultrasonography to rule out VTE in these patients.     

Diagnostic management of clinically suspected acute pulmonary embolism

Summary.  Current diagnostic management of hemodynamically stable patients with clinically suspected acute pulmonary embolism (PE) consists of the accurate and rapid distinction between the approximate 20–25% of patients who have acute PE and require anticoagulant treatment, and the overall majority of patients who do not have the disease in question. Clinical outcome studies have demonstrated that, using algorithms with sequential diagnostic tests, PE can be safely ruled out in patients with a clinical probability indicating PE to be unlikely and a normal D-dimer test result. This obviates the need for additional radiological imaging tests in 20–40% of patients. CT pulmonary angiography (CTPA) has become the first line tool to confirm or exclude the diagnosis of PE in patients with a likely probability of PE or an elevated D-dimer blood concentration. While single-row-detector technology CTPA has a low sensitivity for PE and bilateral compression ultrasound (CUS) of the lower limbs is considered necessary to rule out PE, multi-row-detector CTPA is safe to exclude PE without the confirmatory use of CUS.     

Exclusion of pulmonary embolism using quantitative plasma D-dimer assays

Recent quantitative studies using pulmonary angiography as reference method have indicated that the overall accuracy of quantitative D-dimer assays for the exclusion of pulmonary embolism (PE) in patients suspected of PE is poorer than was reported in earlier studies in which the same D-dimer assays were used (90-94% vs 98-100%). An explanation can be found in the fact that the earlier studies are hampered by the fact that the reference method was a compilation of clinical data and non-invasive diagnostic tests rather than a true gold standard. Furthermore, in those studies no discrimination was made between the milder cases of subsegmental PE and the more severe cases of segmental and larger PE. The lack of a true gold standard and preselection leading to reduced proportions of cases of subsegmental PE in the earlier studies rather than differences in the storage conditions of plasma samples or treatment with heparin, appear to have caused the discrepancies in the reported accuracy of D-dimer assays. It is concluded that the sensitivity and negative predictive values obtained with different quantitative D-dimer assays are in close agreement with each other, that is poor for subsegmental PE and excellent for segmental and larger PE. In diagnostic algorithms D-dimer can reliably exclude acute segmental and/or massive PE. Further work-up within 48 hours is still necessary in negative D-dimer outcomes to exclude subsegmental PE.     

Management of suspected pulmonary embolism (PE) by D-dimer and multi-slice computed tomography in outpatients: an outcome study

OBJECTIVES: A prospective outcome study designed to evaluate a simple strategy for the management of outpatients with suspected pulmonary embolism (PE), based on clinical probability, D-dimer, and multi-slice computed tomography (MSCT). METHODS: A cohort of 432 consecutive patients admitted to the emergency department with suspected PE was managed by sequential non-invasive testing. Patients in whom PE was ruled out were not given anticoagulants, but were followed-up for 3 months. RESULTS: Normal D-dimer and low-intermediate clinical probability ruled out PE in 103 patients [24% (95% CI 20-28)]. Seventeen patients had normal D-dimer, but high clinical probability and proceeded to MSCT. All patients proved negative for PE. A total of 329 (76%) patients underwent MSCT examination. Pulmonary embolism was diagnosed in 93 patients [21.5% (95% CI 18-26)] and was ruled out by negative MSCT in 221 patients [51% (95% CI 46-56)]. MSCT scans were determined as inconclusive in 15 (4.5%) patients. No patient developed objectively verified venous thromboembolism (VTE) during the 3-month follow-up period. However, the cause of death was adjudicated as possibly related to PE in two patients, resulting in an overall 3-month VTE risk of 0.6% (95% CI 0-2.2%). The diagnostic algorithm yielded a definite diagnosis in 96.5% of the patients. CONCLUSIONS: This simple and non-invasive strategy combining clinical probability, D-dimer, and MSCT for the management of outpatients with suspected PE appears to be safe and effective.     

急性肺栓塞性病变的螺旋CT诊断和评价

目的：评价螺旋CT对急性肺栓塞性病变的诊断价值。方法;对临床怀疑急性肺栓塞性病变经螺旋CT诊断及数字减影血管造影（DSA）证实的10例病人作了回顾性分析。观察内容：胸腔积液的有无及多少;肺实质病变的形态;部位及数量;中心及周围肺动脉内有无充盈缺损等。结果：肺栓塞3例,肺梗死7例。除2例混合型外,其余8例均为周围型,下叶居多。结论：肺内楔形实变影可提示急性肺栓塞性病变,若与血管征并存则诊断价值更大。     

Computed tomography of acute pulmonary embolism

Pulmonary embolism (PE) is a common condition in which diagnostic and therapeutic delays contribute to substantial morbidity and mortality. Advances in spiral computed tomography (CT) scanner technology over the past 10 years have been paralleled by progressive improvement in the ability to identify and accurately evaluate the pulmonary arteries for acute PE using CT pulmonary angiography (CTPA). Preliminary studies indicate multi-detector CT (MDCT) scanners offer improved accuracy for distal segmental and subsegmental PE. The ability to directly visualize emboli using CTPA has led to its widespread implementation. Published studies using optimal techniques have found sensitivity and specificity of approximately 90%. Clinical signs and symptoms are nonspecific. Only 20% to 30% of those patients evaluated for acute PE are found to harbor emboli. Previous imaging algorithms offered limited diagnostic value for the remaining 70% to 80% of patients who proved not to have PE. It has been shown that spiral CT identifies an alternate diagnosis in approximately 70% of these patients, which, along with its rapid and widespread availability, largely accounts for its popularity with referring clinicians. It is noted that meta-analysis studies of the existing data regarding spiral CT in acute PE have shown deficiencies in study designs, indicating that further research is required. However, at this time, spiral CT is being widely employed in the diagnostic work-up of patients with suspected acute PE. This review will discuss the use of spiral CT for acute PE, including scan acquisition parameters, radiation dose, diagnostic findings, interpretive pitfalls and the role of leg vein studies.     

Evaluation of a quantitative D-dimer latex immunoassay for acute pulmonary embolism diagnosed by computed tomographic angiography

OBJECTIVE: To determine the sensitivity and specificity of a quantitative plasma fibrin D-dimer latex immunoassay (LIA) for the diagnosis of acute pulmonary embolism. SUBJECTS AND METHODS: Study subjects were Mayo Clinic Rochester inpatients and outpatients with suspected acute pulmonary embolism; all had undergone quantitative D-dimer LIA testing and multidetector-row computed tomographic (CT) angiography between August 3, 2001, and November 10, 2003. Multidetector-row CT angiography was the diagnostic reference standard. RESULTS: Of 1355 CT studies, 208 (15%) were positive for acute pulmonary embolism. Median D-dimer levels were significantly higher for patients with acute pulmonary embolism (1425 ng/mL) than for patients without (500 ng/mL) (P<.001). The highest specificity that optimizes sensitivity for acute pulmonary embolism was achieved by using a discriminant value of 300 ng/mL, which yielded a sensitivity of 0.94 (95% confidence interval [CI], 0.89-0.97), a specificity of 0.27 (95% CI, 0.25-0.30), and a negative predictive value of 0.96 (95% CI, 0.93-0.98). CONCLUSION: The quantitative D-dimer LIA with a discriminant value of 300 ng/mL had high sensitivity and high negative predictive value but low specificity for the diagnosis of acute pulmonary embolism. On the basis of these results, we believe that a negative quantitative D-dimer LIA result and a low pretest probability of thromboembolism together are sufficient to exclude acute pulmonary embolism.