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D-dimer ELISA Identifies Patients at Low Risk for Acute Venous Thromboembolism

A rapid immunoenzymatic assay can exclude patients from further diagnostic testing for acute thromboembolism, suggests a recent Swiss study.

Elevated levels of D-dimer, which are fibrin degradation products, have been observed in patients with venous thromboembolism (VTE). An automated enzyme-linked immunosorbent assay (ELISA) that measures D-dimer levels has greatly aided in the diagnosis of acute thromboembolism in tertiary centers, according to a number of previous trials.

The D-dimer ELISA is a rapid and reliable diagnostic tool whose widespread clinical use would be quite valuable, particularly in emergency care units. Its high negative predictive value allows patients to be discharged more quickly, thereby conserving hospital resources. Moreover, this assay is less expensive and easier to perform than standard invasive or non-invasive procedures.

Thierry Fumeaux, MD, and colleagues at the Regional Hospital, Sion, Switzerland, performed a retrospective diagnostic assessment on 494 patients who were admitted to the emergency department of a secondary care hospital with possible acute VTE and given a D-dimer assay. Six-month follow-up data were collected from hospital records, patient questionnaires, telephone responses, or contact with the patients' physicians.

Upon admission, D-dimer assays were performed simultaneously with clinical evaluation and non-invasive (i.e., venous ultrasound or lung scan) or invasive (i.e., venous or pulmonary angiography) diagnostic tests, but the D-dimer results were not used in diagnosis. Results from the D-dimer assays were later evaluated for their predictive value by comparing assay results with the diagnosis of acute VTE within the follow-up period.

In the course of the study, 110 patients were diagnosed with acute VTE. The D-dimer test correctly predicted VTE in 104 of these patients, detecting D-dimer levels over 500mg/L. However, 6 cases were not correctly predicted and showed negative results in the D-dimer test.

The 6 false-negative results were reported in patients who were evaluated by a physician as having an intermediate or high probability of VTE. This suggests that the D-dimer assay may not be useful in diagnosing this subgroup of patients.

Furthermore, the study confirmed the role of the D-dimer test in excluding low-risk VTE patients in that the assay was very sensitive and could successfully predict patients without risk of VTE (negative predictive value of 96.8%). However, the test lacks specificity and could not predict which patients had VTE.

Dr. Fumeaux and colleagues propose that the D-dimer ELISA can be used "as the initial diagnostic step in the evaluation of clinical suspicion of acute venous thromboembolism in most clinical settings."
J Thromb Haemostas 2003;1:5:976. "The usefulness of five d-dimer assays in the exclusion of deep venous thrombosis"

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