Investigations into the Clinical Utility of Latex D-Dimer in the Diagnosis of Deep Venous Thrombosis

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Abstract
The serial use of non-invasive tests has been shown to be a safe method of managing outpatients who are suspected of having lower limb deep venous thrombosis (DVT). Objective testing has shown that the majority of these outpatients do not have venous thrombosis. A rapid test to exclude DVT in these patients, without the need for expensive and inconvenient serial non-invasive vascular testing, would have practical and economic advantages. Studies measuring the fibrin degradation product D-dimer using enzyme-linked immunoassays (EIA) in patients with veno-graphically proven DVT suggest that it should be possible to exclude this condition by the use of one of the rapid latex bead D-dimer tests. We have examined 190 patients with suspected DVT using both a latex and an EIA D-dimer assay. The latex D-dimer test used in this study was negative in 7 of the 36 proven cases of DVT. This sensitivity of only 80% is not sufficient to allow this type of assay, in its current form, to be used as an exclusion test for DVT. The same plasma samples were tested with an EIA assay. This information was used to mathematically model the effects of selecting a range of D-dimer discriminant cut off points for the diagnosis of DVT. These results indicate that 62% of suspected clinically significant DVT could have this diagnosis excluded, with a 98% sensitivity, if the rapid latex or equivalent D-dimer test could be reformulated to measure less than 185 ng/ml of D-dimer.

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