Clinical Decision Rules May Safely Rule Out Deep Vein Thrombosis

Laurie Barclay, MD

January 20, 2011

January 20, 2011 — Two different decision rules may rule out deep vein thrombosis (DVT) in the primary care setting, according to the results of a study reported online January 17 and published in the January/February issue of the Annals of Family Medicine.

"Despite its widespread accessibility, ultrasonography may not be needed in all patients suspected of DVT," write Eit Frits van der Velde, MD, from the University of Amsterdam, The Netherlands, and colleagues. "The availability of D-dimer (dimerized plasmin fragment D) testing made it possible to combine clinical assessment with this laboratory test to rule out DVT without the need for imaging tests. A diagnostic algorithm, based on a decision rule developed by Wells and colleagues that included information from a patient's medical history and physical examination, followed by D-dimer testing, is now used to guide management in many hospitals worldwide."

Although the Wells rule is effective especially in the secondary care setting, a new clinical decision rule for primary care patients — known as the primary care rule — has recently been proposed because the Wells rule is not sufficient to eliminate DVT in this setting. The goal of this study was to compare the ability of both rules to safely rule out DVT and to efficiently lower the number of referrals for leg ultrasonography that would have negative results.

Before undergoing leg ultrasonography to exclude suspected DVT, 1086 patients provided information to family physicians so that scores for both decision rules could be calculated. Using a rapid point-of-care assay, all patients had D-dimer testing. Based on scoring for each rule and the D-dimer result, patients were stratified into risk categories. The main study endpoints were ultrasonographic diagnosis of DVT and venous thromboembolic complications or death attributed to a possible thromboembolic event during 90-day follow-up. Both rules were compared in terms of the number of missed diagnoses and the proportions of patients that needed ultrasound testing.

The investigators analyzed data from 1002 eligible patients. During follow-up, 7 patients had a venous thromboembolic event, despite a negative D-dimer finding and a low score with the Wells rule (7/447; 1.6%; 95% confidence interval [CI], 0.7% - 3.3%) and with the primary care rule (7/495; 1.4%; 95% CI, 0.6% - 3.0%).

Referral for further testing would not be needed in 447 patients (45%) when using the Wells rule compared with 495 patients (49%) when using the primary care rule (P < .001). Direct medical costs per patient were similar using either rule. The primary care rule is relatively compact and could prevent more unnecessary ultrasound procedures, making it slightly more convenient for both patients and physicians.

Limitations of this study include the possibility that attending physicians documented the "presence of an alternative diagnosis," one of the most important items of the Wells rule, knowing the result of the primary care rule and of the D-dimer test. In addition, the investigators compared the original Wells rule with the primary care rule without the D-dimer test by leaving out the D-dimer assay from the originally developed rule, which may possibly have underestimated the performance of the primary care rule without the D-dimer assay compared with the Wells rule.

"In primary care, suspected DVT can safely be ruled out using either of the 2 rules in combination with a point-of-care D-dimer test," the study authors write. "Both rules can reduce unnecessary referrals for compression ultrasonography by about 50%, though the primary care rule reduces it slightly more."

The Netherlands Organization for Scientific Research supported this study. The study authors have disclosed no relevant financial relationships.

Ann Fam Med. Published online January 17, 2011.

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