Patient Selection and Data Collection

All hospital, clinic, and emergency room patients who underwent lung scanning for suspected pulmonary embolism at the University of Virginia Hospital, Charlottesville, from July 1987 through Feb­ruary 1988 were enrolled in the study at the time the lung scan was ordered. The study protocol was approved by the human subjects committee of the University of Virginia Health Sciences Center.

Plasma samples were obtained as soon as possible after the development of the symptoms or signs that led to the lung scan request. Additional samples of plasma were collected every two to three days up to ten days after the scan. The plasma specimens, collected in EDTA-containing tubes, were separated by centrifu- gation within 24 hours of collection and stored at —20° С until assayed. buy antibiotics canada

At the time the lung scan was ordered, the requesting physician was asked to provide an estimate of the pretest probability of pulmonary embolism (theoretically 0 to 100 percent). This proba­bility served as an index of the clinical suspicion for pulmonary embolism. The lung scans were interpreted in accordance with standard criteria for normal, low probability, intermediate probabil­ity, indeterminate, and high probability ventilation-perfusion pat­terns.8 In addition to the scan result, the patients’ charts were reviewed to obtain the following information: demographic features; clinical characteristics pertinent to the question of pulmonary embolism (eg, symptoms of chest pain or dyspnea); risk factors for venous thromboembolism; presence of conditions known to be associated with detectable plasma DNA (see below); physical findings associated with pulmonary embolism (eg, tachypnea or tachycardia); laboratory tests (eg, arterial blood gases, electrocar­diography, and chest roentgenogram); lower extremity venography and other tests for deep venous thrombosis; lung scan and pulmonary angiography interpretations; and the final physician diagnosis based on the total constellation of relevant information. All test interpre­tations were made and all clinical data were obtained without knowledge of the plasma DNA results.

Patients were excluded from the study if they had a condition other than pulmonary embolism known to be associated with release of DNA into plasma. These are recent major surgery, recent generalized seizures, liver failure, bacterial endocarditis, high doses of corticosteroids, hemodialysis, and systemic lupus erythema­tosus (SLE) with active vasculitis. Patients also were excluded if their clinical symptoms of pulmonary embolism had persisted for more than seven days before the first plasma sample was drawn. The exclusions were made without knowledge of plasma DNA results.
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