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Increasing the efficiency of D-dimer tests

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f252 (Published 16 January 2013) Cite this as: BMJ 2013;346:f252

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Researchers from Canada have designed and tested a strategy of selective D-dimer testing for adults with suspected first deep vein thrombosis (DVT), in an attempt to improve on the current strategy of testing everyone. The selective strategy used the 9 point Wells rule to identify patients at high, moderate, or low clinical risk of DVT. Those at high risk (including all inpatients) skipped the D-dimer test and had immediate venous ultrasonography of the proximal leg veins. Patients at moderate risk had a D-dimer test with a low threshold for a positive result (0.5 μg/mL); those at low risk had a D-dimer test with a higher threshold for a positive result (1 μg/mL). All patients with a positive D-dimer test result had venous ultrasonography.

In a randomised trial, the new strategy looked just as safe and significantly more efficient than a strategy of universal D-dimer testing with a single threshold for a positive test result (0.5 μg/mL). Among patients who did not have a DVT diagnosed, just 0.5% of both groups developed symptomatic venous thromboembolism within three months (4/798 v 4/798; absolute difference 0.0%, 95% CI −0.8% to 0.8%). Patients managed with the selective strategy had significantly fewer D-dimer tests (668/860 (77.7%) v 859/863 (99.5%); absolute difference −21.8%, −24.8% to −19.1%) and significantly fewer ultrasound examinations than controls (438/860 (50.9%) v 505/863 (58.5%); −7.6%, −12.2% to −2.9%). The two strategies diagnosed a similar proportion of patients with DVT (51/869 (5.9%) of the selective strategy group v 56/863 (6.5%) of controls).

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Cite this as: BMJ 2013;346:f252