Combination of a clinical risk assessment score and rapid whole blood D-dimer testing in the diagnosis of deep vein thrombosis in symptomatic patients

Purpose: The clinical diagnosis of deep vein thrombosis (DVT) is unreliable in more than 50% of cases, and, in recent years, plasma D-dimer assays hav e been used to predict the presence of DVT with high sensitivity and negati ve predictive values. This study investigated the use of a rapid whole bloo d test that could be performed and interpreted by the bedside in addition t o a clinically derived risk assessment score (RAS) to determine whether a p ractical and cost-effective clinical model could be developed for the diagn osis and exclusion of DVT in symptomatic patients. Methods: Two hundred consecutive patients who were referred to the vascular laboratory with clinically suspected DVT underwent the following procedure s: (1) clinical assessment and stratification into low, moderate, or high r isk for DVT on the basis of an RAS related to history, symptoms, and physic al examination findings; (2) rapid (5-minute) whole blood D-dimer testing w ith a semi-qualitative agglutination technique on a fingerprick blood sampl e; and (3) color flow duplex ultrasound scanning with standard criteria for the diagnosis of proximal and calf DVT. Results: Forty-six patients (23%) had acute DVT on duplex ultrasound scanni ng. Of these cases, 28 (61%) had proximal DVT and 18 (39%) were confined to the calf. A total of 88 patients were classified as low risk, 67 were clas sified as moderate, and 45 were classified as high risk on the basis of the RAS method. Of the patients who were classified at low risk, 4.5% (4/88) h ad DVT, as compared with 17.9% (12/67) in the moderate clinical risk group and 66.7% (30/45) in the high risk group. Isolated calf DVT was found in 30 % (9/30), 50% (6/12), and 75% (3/4) of the high, moderate, and low risk gro ups, respectively. The sensitivity (8.7%, 26.1%, 65.2%), specificity (45.5% , 64.3%, 90.3%), positive predictive value (4.5%, 17.9%, 66.7%), and overal l accuracy rate (37%, 55.5%, 84.5%) of the low, moderate, and high risk gro ups, respectively, in the diagnosis of DVT increased significantly with inc reasing risk score stratification. The sensitivity, specificity, positive a nd negative predictive value, and overall accuracy of the rapid D-dimer tes t for all DVT were 91.3%, 81.9%, 60%, 96.9%, and 84%, respectively, with a 100% sensitivity and negative predictive value for proximal DVT. A combinat ion of the RAS and D-dimer identified a low risk group with a negative D-di mer as having less than a 1% likelihood of DVT and a high risk group with p ositive D-dimer as having a likelihood of more than 90%. Conclusion: A combination of clinical assessment and rapid D-dimer testing provides an effective means of excluding proximal DVT in symptomatic patien ts. The application of a clinical diagnostic model on the basis of these pa rameters has the potential for saving a large proportion of unnecessary dup lex scans with the associated time and costs.