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Usefulness of the D‐dimer/fibrinogen ratio to predict deep venous thrombosis

D-dimer testing has been shown to be of potential clinical utility in the diagnostic work-up of suspected deep venous thrombosis (DVT) of the lower extremities: D-dimer plasma levels below a certain cut-off can be used for the exclusion of the disease [1,2]. Many different D-dimer tests are commercially available, however, with considerable variation of their reliability [3,4] and only a few have been found to have a sensitivity and a negative predictive value which is high enough to be used in clinical practice [5]. Although D-dimer testing is not able to predict venous thromboembolism due to the low specificity of the tests, we have recently shown that the combination of functional fibrinogen and D-dimer measurements will improve the specificity. A D-dimer/fibrinogen ratio (D/F ratio) above a certain cut-off was found to be highly specific for the presence of acute pulmonary embolism among patients with clinical signs and symptoms of the disease [6]. We therefore investigated the diagnostic performance of the D/F ratio in combination with three established D-dimer tests among outpatients with suspected DVT. Consecutive outpatients referred for diagnostic work-up for suspected DVT of the lower extremity entered the study. Patients were excluded for the following reasons: therapeutic or prophylactic anticoagulation with standard heparin, lowmolecular-weight heparin or oral anticoagulants for more than 24 h prior to study inclusion, pregnancy and hospitalization in the preceding 3 days. Informed consent was obtained from all patients and the study was approved by the Ethics Committee. Diagnosis of DVT was based upon either contrast venography or power-based color-coded duplex ultrasonography. Patients were considered not to have DVT when the initial diagnostic test was normal and clinical 3-month follow-up was uneventful. DVT was classified as proximal when it was localized in the popliteal and/or iliofemoral veins and as distal when localized in the calf veins. Citrated plasma samples were collected and stored at )70 C. The following D-dimer assays were applied: STA Liatest D-Di (Roche Diagnostics AG, Rotkreuz, Switzerland), performed on the STA-R coagulation analyzer [5]; VIDAS D-dimer test (Bio-Mérieux, Lyon, France) [7]; Tinaquant D-dimer (Roche Diagnostics) on a Hitachi analyzer (Roche Diagnostics) [8]. Functional fibrinogen plasma levels were determined using STA Fibrinogen (Roche Diagnostics) on the STA-R coagulation analyzer. C-reactive protein (CRP) was assessed with a high-sensitivity assay on a BN II nephelometer (Dade Behring, Marburg, Germany), allowing detection of values as low as 0.3 mg L [9]. From the 103 patients included, 51 were male and 52 female. Median age was 56.3 years (range 22–88). The overall prevalence of DVT was 44.7% (46/103 patients) and DVT was proximal in 32 (31.1%) and distal in 14 (13.6%) patients. The 3-month follow-up was uneventful in all patients. Table 1 showsD-dimer (Liatest D-Di), fibrinogen, CRP plasma levels and D/F ratios among the patients with no DVT, any DVT, proximal DVT or distal DVT, respectively. The results were comparable to the two other D-dimer tests. Patients with DVT had significantly higherD-dimer values comparedwith patients with no DVT (P < 0.0001, Mann–Whitney U-test), whereas patients with proximal DVT showed significantly higher D-dimer values than patients with distal DVT (P 1⁄4 0.0008). Fibrinogen plasma values were higher in patients with DVT compared with those without; however, the difference was not significant. CRP was significantly (P 1⁄4 0.007) higher in DVT patients compared with those without DVT. We found a significant correlation between fibrinogen plasma values and CRP; however, this correlation was weaker in patients with DVT (rs 1⁄4 0.545, P < 0.001) compared with those without DVT (rs 1⁄4 0.621, P < 0.0001). The D/F ratio was significantly higher among patients with DVT compared with those Correspondence: W. A. Wuillemin, Division of Hematology, Kantonsspital Luzern, 6000 Luzern 16, Switzerland. Tel.: +41 41 205 5147; fax: +41 41 205 2197; e-mail: walter.wuillemin@ ksl.ch