D-dimer testing in the investigation of venous thromboembolism

Plasma D-dimer levels provide a potentially useful tool in evaluating patients with suspected venous thromboembolism. In order to be used safely to exclude VTE, this test must have very high sensitivity and negative predictive value. It must also be sufficiently fast and inexpensive to be used in the evaluation of large numbers of patients. Several different methods exist for measuring D-dimer levels. The new rapid quantitative ELISA assay (e.g. VIDAS) offers the advantages of high sensitivity and negative predictive value, and is faster than the traditional ELISA assay. Many of the automated latex assays also demonstrate high sensitivity, and have the further advantage of being fully automated and faster than even the newer ELISA assays. Use of the D-dimer assay is somewhat limited by its low specificity, especially in older age groups. The physiological increase in serum D-dimer levels with advancing age may mean that effective use of this test is limited to younger individuals. While a negative D-dimer effectively excludes VTE, a positive result may be due to a variety of conditions including inflammation, infection and trauma, as well as DVT or PE. The D-dimer test is best suited for use in the evaluation of suspected DVT or PE in an outpatient setting where the symptoms are of recent onset. As with other laboratory tests, D-dimer evaluation should always be interpreted in the context of clinical assessment. Clinical algorithms that include standardised clinical assessment, sensitive D-dimer measurement, and a systematic approach to imaging modalities are likely to form the cornerstone of the investigation of suspected VTE in the foreseeable future. At present, D-dimer testing is most useful in the case of an appropriate patient with low to moderate clinical probability for VTE, where a negative test result may be used to reach a negative diagnosis. Fortunately, this group represents the majority of patients presenting for assessment. In cases where there is a high degree of clinical suspicion, it is probably inappropriate to use the D-dimer evaluation as a sole test for exclusion of suspected VTE.