OUTPATIENT DUPLEX SCANNING FOR DEEP-VEIN THROMBOSIS - PARAMETERS PREDICTIVE OF A NEGATIVE STUDY RESULT

Purpose: Although clinical examination has been reported to be unrelia ble in the diagnosis of deep vein thrombosis (DVT), this conclusion ha s often been derived from hospitalized patients (HP) and may not be ap plicable in an outpatient setting. This study was undertaken to define clinical parameters that might predict the diagnostic value of emerge ncy venous duplex scanning (VDS). Methods: Venous duplex scans perform ed over a 9-month period (interval I) in 154 outpatients (154 limbs) a nd 145 HP (145 limbs) with suspected DVT were reviewed. Results: Eight een percent of scans of outpatients and 31% of scans of HP were interp reted as positive for lower extremity DVT. With stepwise logistic regr ession analysis, criteria predictive of a negative result of outpatien t 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 prospectively to 68 outpatients (68 limb s) 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 outpatients examined during interv als I and II, 98 (44%) met these three clinical criteria. Three of the se 98 outpatients had DVT on VDS and thus would have been misclassifie d as having a negative result. With a similar logistic regression anal ysis for HP, clinical criteria achieved an NPV of only 75% (sensitivit y 36%, specificity 90%, positive predictive value 62%). Conclusion: Cl inical assessment is unreliable in the diagnostic evaluation of HP wit h suspected DVT. In an outpatient population, however, clinical evalua tion with the above criteria achieved an NPV of 96.7% in the diagnosis of DVT. These parameters may be useful as guidelines in determining t he appropriateness of emergency outpatient VDS.