D-Dimer Assay

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 1993). For example, Masuda et al. (2015) report sensitivity and specificity at 77.3% and 69.2%, respectively, among a sample of 268 individuals with acute traumatic SCI. D-dimer assays have a high negative predictive value, so that when it is negative it is unlikely that the individual 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 individuals admitted with a diagnosis of stroke, SCI (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 and widely available screening test for VTE. It is been utilized to screen for DVT at two weeks after the SCI (Masuda et al. 2015) or on admission to rehabilitation unit from acute care (Eichinger et al. 2018). If levels are high, further investigation is warranted (Wada et al. 2013)