D-Dimer Assay

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D-dimer assay tests are rapid, noninvasive and inexpensive (Gill & Nahum 2000). Fibrin is the main component of thrombus formation and fibrin degradation products include d-dimers (Gill & Nahum 2000). A positive d-dimer test is highly sensitive but lacks specificity since d-dimers are found in other disease states including cancer, congestive heart failure and inflammatory conditions (Raimondi et al. 1993). D-dimer assays have a high negative predictive value, so that when it is negative it is unlikely that the patient has a DVT. However, it has poor positive predictive value so that when it is positive the cause could be a condition other than DVT (i.e., false positive). To illustrate, Akman et al. (2004) reported that the sensitivity and negative predictive values of the D-dimer test were high, at 95.2% and 96.2% respectively, in a group of 68 rehabilitating patients admitted with a diagnosis of stroke, spinal cord injury (n=43%), hip arthroplasty or traumatic brain injury. The specificity and positive predictive value were low, at 55.3% and 48.7%. Therefore, the d-dimer test appears to be a useful test for ruling out venous thromboembolism although a positive test is not diagnostic and must be confirmed with other testing.