Diagnosing DVT in a Primary Care Setting
Diagnosing DVT in a Primary Care Setting
Abstract & Commentary
By Allan J. Wilke, MD, MA, Chair, Department of Integrative Medicine, Ross University School of Medicine, Commonwealth of Dominica. Dr. Wilke reports no financial relationship to this field of study.
Synopsis: The Wells rule for identifying patients at high risk for DVT did not perform as well as one developed from an outpatient population.
Source: van der Velde EF, et al. Comparing the diagnostic performance of 2 clinical decision rules to rule out deep vein thrombosis in primary care patients. Ann Fam Med 2011;9:31-36.
The wells rule1 (wr) was developed in 1995 from a tertiary care referral patient population to rule out deep vein thrombosis (DVT) in patients at very low risk. This group of investigators from the Department of General Practice at the University of Amsterdam previously published their research that WR does not work well in an outpatient population2 and subsequently proposed their own rule (the primary care rule PCR) based on an outpatient population.3 One of their concerns is that WR requires the physician to estimate the probability that there is an alternative diagnosis for the problem that is at least as likely as DVT. They reasoned that since the prevalence of DVT is low in primary care (incidence ~1%4), the physician might not have a different diagnosis. A comparison of the two rules is contained in Table 1. The cutoff scores for high risk are 2 for WR and 4 for PCR.
Table 1. Comparison of WR and PCR
|
Test |
High-risk |
Low-risk |
|
WR |
373 |
629 |
|
PCR |
152 |
850 |
In this study, they compared the performance of WR and PCR using their original research population. The subjects were patients with suspected DVT who presented to more than 300 Dutch general practitioners. Inclusion criteria were: age > 18 years and at least one of the following symptoms: swelling, redness, or lower extremity pain. They excluded patients taking a low-molecular-weight heparin or vitamin K antagonist. The 1002 subjects averaged 58 years and were 37% male. Subjects scoring 4 and above were referred for compression ultrasound (CUS). All other patients were assumed to not have a DVT, and thus were not referred for CUS nor started on an anticoagulant. Patients followed up with their physicians after about 1 week, and 3 months after entering the study they received a questionnaire.
PCR relies on the results of the d-dimer test as part of its scoring scheme. WR does not use d-dimer results in its score; patients with a low score, followed by a negative d-dimer are considered to be at low risk and are not referred for CUS. For an "apples-to-apples" evaluation, these researchers compared the two scores with and without the d-dimer results. In the first analysis, patients who scored ≤ 1 on the WR were labeled low risk. Patients who scored ≥ 2 were labeled high risk. Similarly, according to PCR, patients who scored ≤ 3 were low risk, and ≥ 4 were high risk. The results of the d-dimer test were not considered. In the second scenario (addition of d-dimer), the low-risk WR patients had a score ≤ 1 AND a negative d-dimer. High-risk patients had a score ≥ 2 OR a positive d-dimer. Similarly, low-risk PCR patients had a score ≤ 3 AND a negative d-dimer, and high-risk patients had a score ≥ 4 OR a positive d-dimer, which by itself scores 6.
The outcomes of interest were test safety (percentage of low-risk patients who within 3 months had developed a thromboembolic event) and test efficiency (how many patients were labeled high risk and required CUS). A thromboembolic event was defined as pulmonary embolism or DVT. The better test would identify all patients who would either have or go on to have a thromboembolic event, while sending fewer patients for CUS.
One hundred thirty-six (14%) of the 1002 subjects had DVT. In both low-risk groups, 7 patients subsequently had a thromboembolic event at 3-month follow-up. Three subjects were lost to follow-up.
The performance of the two tests without d-dimer is summarized in Table 2. For safety, PCR had a better rate (0.08% vs. 1.1%). Regarding efficiency, WR identified 121 more patients than PCR as being high-risk and requiring CUS.
Table 2. Performance of tests without d-dimer
|
Variables |
WR |
PCR |
|
Male sex |
NA |
1 |
|
Oral contraceptive use |
NA |
1 |
|
Active cancer (treatment ongoing or within previous 6 months or palliative) |
1 |
1 |
|
Paralysis, paresis, or recent plaster immobilization of the lower extremities |
1 |
NA |
|
Major surgery (last 3 months) |
1 |
1 |
|
Absence of leg trauma |
NA |
1 |
|
Localized tenderness along the distribution of the deep venous system |
1 |
NA |
|
Dilated collateral veins (not varicose) |
1 |
1 |
|
Entire leg swelling |
1 |
NA |
|
Calf swelling ≥ 3 cm larger than the asymptomatic leg |
1 |
2 |
|
Pitting edema confined to the symptomatic leg |
1 |
NA |
|
Previously documented DVT |
1 |
NA |
|
Alternative diagnosis at least as likely as DVT |
-2 |
NA |
|
Positive d-dimer result |
NA |
6 |
|
Cutoff scores for considering DVT as absent |
≤ 1 |
≤ 3 |
The performance of the two tests with d-dimer is summarized in Table 3. In this situation, PCR and WR safety was nearly identical (1.4% vs. 1.6%). WR referred 48 more patients for CUS than PCR.
The two tests did not always agree. When the d-dimer results were not considered, 22 patients identified as high risk by PCR scored as low risk by WR, and 243 high-risk WR patients were low risk by PCR. The 7 patients who were low risk by PCR and who subsequently had a thromboembolic event were not the same 7 in the WR group. The overlap was 4.
Table 3. Performance of tests with d-dimer
|
Test |
High-risk |
Low-risk |
|
WR |
555 |
447 |
|
PCR |
507 |
495 |
Commentary
The technology for diagnosing DVT has progressed along two fronts, imaging and biochemical. Compression ultrasound, which demonstrates the presence of a noncompressible vein, confirms the diagnosis, but costs at least 10 times what a d-dimer does. As was demonstrated in this study, a negative d-dimer no matter which rule was used did not rule out thromboembolic events absolutely, and a positive one does not clinch the diagnosis. Point-of-care d-dimer tests are available, which, if negative, could save your patient a trip to an imaging center. Both rules performed well, but PCR appears to be more cost effective.
References
1. Scarvelis D, Wells PS. Diagnosis and treatment of deep-vein thrombosis. CMAJ 2006;175:1087-1092.
2. Oudega R, et al. The wells rule does not adequately rule out deep venous thrombosis in primary are patients. Ann Intern Med 2005;143:100-107.
3. Oudega R, et al. Ruling out deep venous thrombosis in primary care. A simple diagnostic algorithm including D-dimer testing. Thromb Haemost 2005;94:200-205.
4. U.S. Department of Health and Human Services. The Surgeon General's Call to Action to Prevent Deep Vein Thrombosis and Pulmonary Embolism-2008. Available at: http://www.surgeongeneral.gov/topics/deepvein/calltoaction/call-to-action-on-dvt-2008.pdf. Accessed March 7, 2011.
The Wells rule for identifying patients at high risk for DVT did not perform as well as one developed from an outpatient population.Subscribe Now for Access
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