Practical utility of the D-dimer assay for excluding thromboembolism in severely injured trauma patients

Background. We have advocated the use of a D-dimer assay to exclude the dia gnosis of pulmonary embolism (PE) and deep venous thrombosis (DVT) in surgi cal and trauma patients suspected of having these diagnoses. Injury is know n to increase D-dimer levels independent of thromboembolism. The purpose of this study was to assess the period after injury over which the D-dimer as say remains positive because of injury exclusive of thromboembolism. Methods. We prospectively sampled the plasma of severely injured patients f or D-dimer using an enzyme-linked immunosorbent assay method at admission; at hours 8, 16, 24, and 48; and at days 3, 4, 5, and 6. Patients were then screened for DVT with a routine duplex Doppler at day 7. Patients were foll owed for PE, adult respiratory distress syndrome, and disseminated intravas cular coagulation. Results. One hundred fifty-four patients (mean Injury Severity Score of 23) underwent a total of 1,230 D-dimer assays. Twenty-six (17%) had thromboemb olism. Nine (6%) patients developed DVT, 2 (1%) developed PE, 13 (8%) devel oped disseminated intravascular coagulation, and 11 (7%) developed severe a dult respiratory distress syndrome. None of the trauma patients with thromb oembolism had a (false) negative D-dimer at or after the time of their thro mboembolic complication. True-negative D-dimer results as a function of tim e from injury are: 0 hours, 18%; 8 hours, 16%; 16 hours, 17%; 24 hours, 22% ; 48 hours, 37%; day 3, 34%; day 4, 32%; day 5, 30%; and day 6, 30%. The ne gative predictive value of the assay was 100%. D-dimer levels were signific antly higher in those who developed a thromboembolic complication than in t hose who did not (independent of Injury severity Score). Conclusion. These data serve to validate D-dimer as a means of excluding th romboembolism, specifically in patients with severe injury (100% negative p redictive value). Before 48 hours after injury, however, the vast majority of these patients without thromboembolism had positive D-dimer assays. Beca use of the high false-positive rate early after severe injury, the D-dimer assay may be of little value before postinjury hour 48.