***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: OBJECTIVE This study was design ed to prospect ively compare helical CT with pulmonary angiography in the detection of pulmonary embolism in patients with an unresolved clinical and scintigraphic diagnosis . SUBJECTS AND METHODS Twenty patients with an unresolved suspicion of pulmonary embolism were evaluated with contrast-enhanced helical CT and with selective pulmonary angiography . An average of 11 hr separated the two studies . The CT scans were obtained during one 24-sec or two 12-sec breath-holds . CT scans were interpreted without knowledge of the results of scintigraphy or angiography . Selective pulmonary angiograms were obtained with knowledge of the findings on the ventilation/perfusion scan only . The sensitivity and specificity of CT were compared with those of angiography for central vessels ( segmental and larger ) only and for all vessels . RESULTS Eleven of the 20 patients had proved pulmonary embolism ( seven in central vessels and four in subsegmental vessels only ) . When only central vessels were analyzed , CT sensitivity was 86 % , specificity was 92 % , and the likelihood ratio was 10.7 . However , when subsegmental vessels were included , CT results were 63 % , 89 % , and 5.7 , respectively . CONCLUSION In our subset of patients , helical CT was only 63 % sensitive . Subsegmental emboli are difficult to diagnose . Pulmonary angiography remains the study of choice . CT has a limited role in the evaluation of acute pulmonary embolism Background —Serial ultrasonography is reliable for the diagnosis of deep venous thrombosis in symptomatic patients , but the low prevalence of thrombosis in this group renders the approach costly and inconvenient to patients . We studied the clinical validity of the combination of a pretest clinical probability score and a D-dimer test in the initial evaluation of patients suspected of deep venous thrombosis . Methods and Results — Patients with a normal D-dimer concentration ( < 500 fibrin equivalent units [ FEU ] & mgr;g/L ) and a non-high probability score ( <3 ) had no further testing . Patients with a normal D-dimer concentration and a high probability score ( ≥3 ) underwent one ultrasonogram . Serial ultrasonography was performed in patients with an abnormal D-dimer concentration . Patients were followed for 3 months . A total of 812 patients were evaluable for efficacy . Only 1 of 176 patients ( 0.6 % ; 95 % CI , 0.02 % to 3.1 % ) with a normal D-dimer concentration and a non-high probability score developed thrombosis during follow-up . A normal D-dimer concentration and a high probability score were found in 39 patients ; 3 of them ( 7.7 % ; 95 % CI , 1.6 % to 20.9 % ) had thrombosis at presentation , and one ( 2.8 % ; 95 % CI , 0.07 % to 14 . 5 % ) developed pulmonary embolism during follow-up . In 306 of 597 patients ( 51.3 % ) with an abnormal D-dimer concentration , thrombosis was detected by serial ultrasonography . Six patients ( 2.1 % ; 95 % CI , 0.8 % to 4 . 4 % ) developed thrombosis during follow-up . No deaths due to thromboembolism occurred during follow-up . The total need for ultrasonography  was reduced by 29 % . Conclusion —The combination of a non-high pretest clinical probability score and a normal D-dimer concentration is a safe strategy to rule out deep venous thrombosis and to withhold anticoagulation OBJECTIVE To vali date the predictive value of the Canadian clinical probability model for acute venous thrombosis , which , to the best of the authors ' knowledge , has not been done in emergency department ( ED ) setting s outside of Canada . METHODS Demographic and clinical information , rapid D-dimer testing , and venous ultrasound imaging  were obtained among patients presenting with clinical ly suspected venous thrombosis at a university-affiliated ED . A diagnosis of deep venous thrombosis ( DVT ) was made based on venous ultrasound test results or objective ly documented venous thromboembolism during a 12-week follow-up period . The probability of venous thrombosis was calculated using the Canadian clinical probability model . RESULTS Among 102 patients , 17 ( 17 % ) were diagnosed as having  venous thrombosis  initially or during the three-month follow-up period . The frequency of venous thrombosis among patients categorized as having high probability was 10 of 17 [ 59 % , 95 % confidence interval ( 95 % CI ) = 35 % to 82 % ] , 6 of 44 ( 14 % , 95 % CI = 4 % to 24 % ) with intermediate probability , and 1 of 41 ( 2 % , 95 % CI = 0.1 % to 11 % ) with low probability . This compares with respective values of 49 % , 14 % , and 3 % , reported by Canadian research ers in an ED study . Forty-one of 102 ( 40 % ) patients had an alternate diagnosis as likely or more likely than venous thrombosis , but only three ( 7 % , 95 % CI = 2 % to 18 % ) of these had venous thrombosis . CONCLUSIONS Use of the Canadian probability model for DVT in this ED result ed in effective risk stratification , comparable to previously published results PURPOSE Although clinical examination has been reported to be unreliable in the diagnosis of deep vein thrombosis  ( DVT ) , this conclusion has often been derived from hospitalized patients ( HP ) and may not be applicable in an outpatient setting . This study was undertaken to define clinical parameters that might predict the diagnostic value of emergency venous duplex scanning ( VDS ) . METHODS Venous duplex scans performed over a 9-month period ( interval I ) in 154 out patients ( 154 limbs ) and 145 HP ( 145 limbs ) with suspected DVT were review ed . RESULTS Eighteen percent of scans of out patients and 31 % of scans of HP were interpreted as positive for lower extremity DVT . With stepwise logistic regression analysis , criteria predictive of a negative result of outpatient VDS included ( 1 ) duration of symptoms greater than 7 days ( p = 0.003 ) , ( 2 ) thigh circumference difference relative to the uninvolved side of less than 3 cm ( p = 0.001 ) , and ( 3 ) no history of neoplasia ( p = 0.03 ) . This model , when applied prospect ively to 68 out patients ( 68 limbs ) over the next 5 months ( interval II ) , yielded a negative predictive value ( NPV ) of 96.7 % ( sensitivity 90.9 % , specificity 50.9 % , positive predictive value 26.3 % ) . Of the 222 out patients examined during intervals I and II , 98 ( 44 % ) met these three clinical criteria . Three of these 98 out patients had DVT on VDS and thus would have been misclassified as having a negative result . With a similar logistic regression analysis for HP , clinical criteria achieved an NPV of only 75 % ( sensitivity 36 % , specificity 90 % , positive predictive value 62 % ) . CONCLUSION Clinical assessment is unreliable in the diagnostic evaluation of HP with suspected DVT . In an outpatient population , however , clinical evaluation with the above criteria achieved an NPV of 96.7 % in the diagnosis of DVT . These parameters may be useful as guidelines in determining the appropriateness of emergency outpatient VDS We have previously demonstrated that a clinical model can be safely used in a management strategy in patients with suspected pulmonary embolism ( PE ) . We sought to simplify the clinical model and determine a scoring system , that when combined with D-dimer results , would safely exclude PE without the need for other tests , in a large proportion of patients . We used a r and omly selected sample of 80 % of the patients that participated in a prospect i ve cohort study of patients with suspected PE to perform a logistic regression analysis on 40 clinical variables to create a simple clinical prediction rule . Cut points on the new rule were determined to create two scoring systems . In the first scoring system patients were classified as having low , moderate and high probability of PE with the proportions being similar to those determined in our original study . The second system was design ed to create two categories , PE likely and unlikely . The goal in the latter was that PE unlikely patients with a negative D-dimer result would have PE in less than 2 % of cases . The proportion of patients with PE in each category was determined overall and according to a positive or negative SimpliRED D-dimer result . After these determinations we applied the models to the remaining 20 % of patients as a validation of the results . The following seven variables and assigned scores ( in brackets ) were included in the clinical prediction rule : Clinical symptoms of DVT ( 3.0 ) , no alternative diagnosis ( 3.0 ) , heart rate > 100 ( 1.5 ) , immobilization or surgery in the previous four weeks ( 1.5 ) , previous DVT/PE ( 1.5 ) , hemoptysis ( 1.0 ) and malignancy ( 1.0 ) . Patients were considered low probability if the score was < 2.0 , moderate of the score was 2.0 to 6.0 and high if the score was over 6.0 . Pulmonary embolism unlikely was assigned to patients with scores < or = 4.0 and PE likely if the score was > 4.0 . 7.8 % of patients with scores of less than or equal to 4 had PE but if the D-dimer was negative in these patients the rate of PE was only 2.2 % ( 95 % CI = 1.0 % to 4.0 % ) in the derivation set and 1.7 % in the validation set . Importantly this combination occurred in 46 % of our study patients . A score of < 2.0 and a negative D-dimer results in a PE rate of 1.5 % ( 95 % CI = 0.4 % to 3.7 % ) in the derivation set and 2.7 % ( 95 % CI = 0.3 % to 9.0 % ) in the validation set and only occurred in 29 % of patients . The combination of a score < or = 4.0 by our simple clinical prediction rule and a negative SimpliRED D-Dimer result may safely exclude PE in a large proportion of patients with suspected PE An optimal approach to the diagnosis of deep vein thrombosis ( DVT ) in lower limbs in the emergency department is still unknown . In this prospect i ve cohort study , we aim ed to evaluate the accuracy of the widely available plasma D-dimer test ( VIDAS ) and establish the usefulness of combining D-dimer testing with a clinical model to reduce the need for serial ultra-sonographies and improve the diagnostic strategy of DVT . We performed a cohort study in 383 consecutive out patients referred to the emergency department of Hospital La Princesa , with clinical suspicion of DVT . The patients were stratified into three pre-test probability categories using an explicit clinical model ( Wells score ) , and underwent a quantitative automated ELISA D-dimer assay ( VIDAS D-Dimer bioMérieux ) . Patients were managed according to the diagnostic strategy based on clinical probability and compression ultrasonography ( CU ) . Patients for whom DVT was considered a high pre-test probability with negative ultrasonographic findings in the initial CU , returned the following week for repeat ultrasonography . All patients with DVT excluded did not receive anticoagulant therapy , and were followed up for three months to monitor the development of venous thromboembolic complications . DVT was confirmed in 102 patients ( 26.6 % ) : 95 in the initial test , four in the second test , and three who developed venous thromboembolic complications in the three-month follow-up period . The calculated D-dimer cut-off level was 1 micro g/ml . One hundred patients ( 98 % ) with DVT had positive D-dimer . D-dimer had a sensitivity of 98 % and a negative predictive value of 98.6 % . Among the high-probability patients with positive D-dimer tests and initial negative CU , 9.75 % had DVT on repeat CU at one week . The study results suggest that the addition of VIDAS D-dimer to this diagnostic algorithm could improve the management of patients with suspected DVT in daily practice . A diagnostic approach of DVT based on D-dimer ( cut-off > or = 1 microg/ml ) as the first diagnostic tool for the exclusion of DVT , and the clinical probability model as the tool that identifies those patients requiring a second ultrasonography is useful and suitable for daily medical practice BACKGROUND The st and ard diagnostic approach in patients with suspected deep vein thrombosis is to repeat the compression ultrasonography after 1 week in all patients with an initial normal result . We hypothesized that a normal finding of a D-dimer assay safely obviates the need for repeated ultrasonography . In addition , we evaluated the potential value of a pretest probability assessment for this purpose . METHODS At presentation , consecutive out patients with suspected thrombosis underwent independent assessment by means of ultrasonography of the proximal veins , a whole-blood D-dimer assay , and a pretest clinical model . Patients with normal ultrasonographic findings and an abnormal D-dimer assay result were scheduled for repeated ultrasonography . We evaluated the incidence of symptomatic venous thromboembolic complications during a 3-month follow-up , and the value of clinical pretest probability with ultrasonography or D-dimer assay in scenario analyses . RESULT 
    Output:
    
The evidence strongly supports the use of clinical prediction rules , particularly the Wells model , for establishing the pretest probability of DVT or pulmonary embolism in a patient before ordering more definitive testing .