A Comparison between Venometry and D-Dimer in Screening for Deep Vein Thrombosis

Abstract number: P1071

Williams¹ D, Webster¹ J, Watson² HG

¹¹Department of Medicine, Aberdeen Royal Infirmary, Foresterhill, Aberdeen, Scotland, UK ²²Department of Haematology, Aberdeen Royal Infirmary, Foresterhill, Aberdeen, Scotland, UK

Low rates of confirmed diagnoses in suspected cases of DVT dictate that sensitive screening methods that exclude DVT are utilised. There are data, which indicate that appropriate D-dimer tests and computer assisted strain gauge plethysmography (venometry) may be suitable screening tests for this purpose. We compared the performance of these methods in a prospective study of patients with suspected DVT in a single centre. 243 consecutive patients attending a specific DVT diagnostic clinic were assessed by a management algorithm using clinical risk score and the screening tests [D-dimer (VIDAS), venometry] with all positive diagnoses made by compression ultrasound. All cases where DVT was excluded were followed up at 6 weeks. 35/234 (14.4%) had DVT. In the low risk group negative predictive value, sensitivity and specificity of D-dimer versus venometry were (95% CI); 100 vs. 95.6 (95.5, 95.7), 100 vs. 50 (41.8, 58.2) and 49.4 (48.8, 50) vs. 78.3 (77.9, 78.7). Combining the two modalities (either positive) did not improve sensitivity or negative predictive value of D-dimer alone. Applying Bayes theorem to the pretest odds indicates that in patients with negative screening tests the probabilities of having a DVT in low and moderate risk groups were 0 and 6% for D-dimer and 1.8% and 13.7% for venometry respectively. These data indicate that D-dimer testing using this assay is superior to venometry in excluding DVT in low risk patients. Based on combined assessment of clinical risk along with screening test neither modality could be used to safely exclude DVT in moderate risk patients in our experience.