Samantha Malm, MD

BACKGROUND: More than 260,000 cases of pulmonary embolism (PE) are diagnosed each year in the United States. However, the prevalence of PE is estimated to be only 25% to 35% of suspected cases. Commonly used noninvasive diagnostic tools (D-dimer levels, ventilation/perfusion scan, doppler ultrasonography) are inconclusive in a significant number of cases, leading to invasive testing with angiography. Helical computerized tomography (CT) scanning has been suggested by some as a useful test in the diagnosis of PE. This article attempts to address the role of this test in the diagnostic evaluation of those with suspected PE.

POPULATION STUDIED: We studied all adult patients (older than 6 years) presenting to the emergency department of a community teaching hospital in Geneva, Switzerland, over a 25-month period with suspected pulmonary embolism and elevated plasma D-dimer level greater than 500 μg/L. Of the initial 1108 patients enrolled in the study, 35% were excluded on the basis of a normal D-dimer level. Another 38% were excluded on the basis of reasonable criteria (ie, contraindication to CT, declining to participate, taking oral anticoagulants, CT results unavailable or unblinded). There was no clinically significant difference in age, sex, risk factors, clinical presentation, and clinical probability of PE between those included and those excluded.

STUDY DESIGN AND VALIDITY: This was a prospective cohort study in which 229 patients were evaluated and treated according to the hospital’s current practices. In addition to the usual studies, CT scans were performed on all patients, with results withheld from the treating physician so as to not influence diagnosis and treatment. CT interpretation was performed more than 3 months after acquisition of the films by 3 radiologists who were blinded to all other clinical data and test results. PE was diagnosed if the patient had a positive angiogram, a high-probability lung scan, or DVT and a clinical suspicion of PE. PE was ruled out if the patient had a normal angiogram, a normal or near-normal lung scan, or low clinical suspicion with a nondiagnostic lung scan and no evidence of DVT. Results from the CT were compared with these gold standards. In addition, patients were followed for 3 months for evidence of DVT or PE. It is important to note that the results of the study can only be applied to patients initially presenting as outpatients who were found to have elevated D-dimer levels. The study is well done. The gold standards chosen are reasonable, and the patient population is appropriate; these are the patients for whom the question of whether to proceed to angiography is important.

OUTCOMES MEASURED: Sensitivity and specificity of helical CT in diagnosing PE with and without other diagnostic modalities.

RESULTS: Approximately 40% of the 299 patients with positive D-dimer levels were eventually found to have PE (prevalence = 40%). Of these, the helical CT scan correctly identified 70% (confidence interval [CI], 62%-78%) of patients with embolism and correctly identified as negative 91% (CI, 86%-95%) of patients without embolism (positive likelihood ratio=8.0; negative likelihood ratio=0.3). These results were unchanged by the application of more stringent diagnostic criteria (high-probability scan, low-probability scan, or angiography). The false-negative rate of 30% decreased to 21% in patients who had a positive D-dimer level but negative ultrasound before CT. When used as a fourth-line diagnostic test, after a positive D-dimer, normal ultrasound, and inconclusive pulmonary scan, the false-negative rate decreased to 5% and the false-positive rate decreased to 7%.

BACKGROUND: More than 260,000 cases of pulmonary embolism (PE) are diagnosed each year in the United States. However, the prevalence of PE is estimated to be only 25% to 35% of suspected cases. Commonly used noninvasive diagnostic tools (D-dimer levels, ventilation/perfusion scan, doppler ultrasonography) are inconclusive in a significant number of cases, leading to invasive testing with angiography. Helical computerized tomography (CT) scanning has been suggested by some as a useful test in the diagnosis of PE. This article attempts to address the role of this test in the diagnostic evaluation of those with suspected PE.

POPULATION STUDIED: We studied all adult patients (older than 6 years) presenting to the emergency department of a community teaching hospital in Geneva, Switzerland, over a 25-month period with suspected pulmonary embolism and elevated plasma D-dimer level greater than 500 μg/L. Of the initial 1108 patients enrolled in the study, 35% were excluded on the basis of a normal D-dimer level. Another 38% were excluded on the basis of reasonable criteria (ie, contraindication to CT, declining to participate, taking oral anticoagulants, CT results unavailable or unblinded). There was no clinically significant difference in age, sex, risk factors, clinical presentation, and clinical probability of PE between those included and those excluded.

STUDY DESIGN AND VALIDITY: This was a prospective cohort study in which 229 patients were evaluated and treated according to the hospital’s current practices. In addition to the usual studies, CT scans were performed on all patients, with results withheld from the treating physician so as to not influence diagnosis and treatment. CT interpretation was performed more than 3 months after acquisition of the films by 3 radiologists who were blinded to all other clinical data and test results. PE was diagnosed if the patient had a positive angiogram, a high-probability lung scan, or DVT and a clinical suspicion of PE. PE was ruled out if the patient had a normal angiogram, a normal or near-normal lung scan, or low clinical suspicion with a nondiagnostic lung scan and no evidence of DVT. Results from the CT were compared with these gold standards. In addition, patients were followed for 3 months for evidence of DVT or PE. It is important to note that the results of the study can only be applied to patients initially presenting as outpatients who were found to have elevated D-dimer levels. The study is well done. The gold standards chosen are reasonable, and the patient population is appropriate; these are the patients for whom the question of whether to proceed to angiography is important.

OUTCOMES MEASURED: Sensitivity and specificity of helical CT in diagnosing PE with and without other diagnostic modalities.

RESULTS: Approximately 40% of the 299 patients with positive D-dimer levels were eventually found to have PE (prevalence = 40%). Of these, the helical CT scan correctly identified 70% (confidence interval [CI], 62%-78%) of patients with embolism and correctly identified as negative 91% (CI, 86%-95%) of patients without embolism (positive likelihood ratio=8.0; negative likelihood ratio=0.3). These results were unchanged by the application of more stringent diagnostic criteria (high-probability scan, low-probability scan, or angiography). The false-negative rate of 30% decreased to 21% in patients who had a positive D-dimer level but negative ultrasound before CT. When used as a fourth-line diagnostic test, after a positive D-dimer, normal ultrasound, and inconclusive pulmonary scan, the false-negative rate decreased to 5% and the false-positive rate decreased to 7%.

BACKGROUND: More than 260,000 cases of pulmonary embolism (PE) are diagnosed each year in the United States. However, the prevalence of PE is estimated to be only 25% to 35% of suspected cases. Commonly used noninvasive diagnostic tools (D-dimer levels, ventilation/perfusion scan, doppler ultrasonography) are inconclusive in a significant number of cases, leading to invasive testing with angiography. Helical computerized tomography (CT) scanning has been suggested by some as a useful test in the diagnosis of PE. This article attempts to address the role of this test in the diagnostic evaluation of those with suspected PE.

POPULATION STUDIED: We studied all adult patients (older than 6 years) presenting to the emergency department of a community teaching hospital in Geneva, Switzerland, over a 25-month period with suspected pulmonary embolism and elevated plasma D-dimer level greater than 500 μg/L. Of the initial 1108 patients enrolled in the study, 35% were excluded on the basis of a normal D-dimer level. Another 38% were excluded on the basis of reasonable criteria (ie, contraindication to CT, declining to participate, taking oral anticoagulants, CT results unavailable or unblinded). There was no clinically significant difference in age, sex, risk factors, clinical presentation, and clinical probability of PE between those included and those excluded.

STUDY DESIGN AND VALIDITY: This was a prospective cohort study in which 229 patients were evaluated and treated according to the hospital’s current practices. In addition to the usual studies, CT scans were performed on all patients, with results withheld from the treating physician so as to not influence diagnosis and treatment. CT interpretation was performed more than 3 months after acquisition of the films by 3 radiologists who were blinded to all other clinical data and test results. PE was diagnosed if the patient had a positive angiogram, a high-probability lung scan, or DVT and a clinical suspicion of PE. PE was ruled out if the patient had a normal angiogram, a normal or near-normal lung scan, or low clinical suspicion with a nondiagnostic lung scan and no evidence of DVT. Results from the CT were compared with these gold standards. In addition, patients were followed for 3 months for evidence of DVT or PE. It is important to note that the results of the study can only be applied to patients initially presenting as outpatients who were found to have elevated D-dimer levels. The study is well done. The gold standards chosen are reasonable, and the patient population is appropriate; these are the patients for whom the question of whether to proceed to angiography is important.

OUTCOMES MEASURED: Sensitivity and specificity of helical CT in diagnosing PE with and without other diagnostic modalities.

RESULTS: Approximately 40% of the 299 patients with positive D-dimer levels were eventually found to have PE (prevalence = 40%). Of these, the helical CT scan correctly identified 70% (confidence interval [CI], 62%-78%) of patients with embolism and correctly identified as negative 91% (CI, 86%-95%) of patients without embolism (positive likelihood ratio=8.0; negative likelihood ratio=0.3). These results were unchanged by the application of more stringent diagnostic criteria (high-probability scan, low-probability scan, or angiography). The false-negative rate of 30% decreased to 21% in patients who had a positive D-dimer level but negative ultrasound before CT. When used as a fourth-line diagnostic test, after a positive D-dimer, normal ultrasound, and inconclusive pulmonary scan, the false-negative rate decreased to 5% and the false-positive rate decreased to 7%.