Impedance plethysmography or ultrasonography were effective for detecting deep-vein thrombosis
ACP J Club. 1993 Mar-April;118:50. doi:10.7326/ACPJC-1993-118-2-050
Heijboer H, Cogo A, Büller HR, Prandoni P, ten Cate JW. Detection of deep-vein thrombosis with impedance plethysmography and real-time compression ultrasonography in hospitalized patients. Arch Intern Med. 1992 Sep;152:1901-3.
To compare impedance plethysmography (IPG) and real-time compression ultrasonography (US) for detecting suspected deep-vein thrombosis (DVT) in hospitalized patients.
Independent, blinded comparison of IPG and US with ascending contrast venography.
2 university hospitals in the Netherlands and Italy.
83 of 127 consecutive hospitalized patients (mean age 60 y, 58% women) with suspected DVT. 44 excluded patients had contraindications for venography (n = 14), were unable to have venography (n = 11), were taking anticoagulant or thrombolytic therapy (n = 13), had previously had a confirmed episode of DVT in the same leg within 1 year (n = 1), were < 18 years old (n = 1), or refused (n = 4).
Description of tests and diagnostic standard
Patients had both IPG and US, done in random order, 1 day before having venography. All 3 tests were interpreted blinded to other test results. US examined the common femoral vein in the groin, the popliteal vein from the popliteal fossa to the region of its trifurcation, and proximal portions of the deep calf veins in the transverse planes only. Results were scored as normal, abnormal, or inadequate for interpretation. Ascending contrast venography was done according to Rabinov and Paulin with ankle tourniquets to improve filling of the deep venous system. A venograph was considered positive if a constant intraluminal filling defect was present on ≥ 2 projections, or if persistent nonfilling of a venous segment occurred despite repeated injections of dye. 3 experts reviewed all venographs.
Venography was unsuccessful in 4 patients. 53% of the remaining patients had DVT, 45% had thrombi extending into the proximal veins, and 8% had calf-vein thrombi. For proximal vein thrombosis, and for all DVTs the sensitivity, specificity, and positive and negative likelihood ratios were similar (Table).
For proximal vein thrombosis, the positive and negative predictive values were 82% and 97% for IPG and 87% and 97% for US; for all DVTs they were 83% and 91% for IPG and 85% and 94% for US.
Both impedance plethysmography and real-time compression ultrasonography, compared with ascending contrast venography, were effective noninvasive tests for excluding suspected deep-vein thrombosis in hospitalized patients. 15% of patients with positive results from either test did not have deep-vein thrombosis.
Source of funding: Trombosestichting.
For article reprint: Dr. H. Heijboer, Centre for Haemostasis, Thrombosis, Atherosclerosis and Inflammation Research, F4 Room 131, Academic Medical Centre, Amsterdam, Netherlands. FAX 31-20- 696-8833.
Table. Estimated test characteristics for diagnosing deep-vein thrombosis*
|Test for proximal vein thrombosis||Sensitivity (95% CI)||Specificity (CI)||+LR (CI)||-LR (CI)|
|IPG||96% (82 to 100)||83% (67 to 94)||5.18 (3.0 to 12.3)||0.04 (0.01 to 0.21)|
|US||97% (85 to 100)||86% (71 to 95)||6.99 (3.4 to 16.0)||0.03 (0.01 to 0.17)|
|Test for all deep-vein thromboses||Sensitivity||Specificity||+LR||-LR|
|IPG||91% (76 to 98)||83% (67 to 94)||5.45 (12.8 to 11.6)||0.11 (0.04 to 0.29)|
|US||95% (84 to 99)||81% (64 to 92)||4.89 (2.7 to 9.8)||0.06 (0.02 to 0.20)|
*IPG = impedance plethysmography; US = ultrasonography; +LR = likelihood ratio for presence of the disease if the test is positive; -LR = likelihood ratio if the test is negative. LRs calculated from data in article.
Radiocontrast venography is the gold standard for the diagnosis of DVT. Venography, however, is expensive, invasive, and involves risks including radiocontrast allergy, renal failure, and DVT itself. For these reasons, noninvasive approaches have been widely used in patients with suspected DVT.
Three of the most commonly used diagnostic tests for DVT are IPG, duplex ultrasound, and color Doppler ultrasound. IPG measures the rate of blood flow from the leg and is abnormal if thrombi occlude the femoral or iliac vein. Duplex ultrasound visualizes the veins of the thigh, and DVT is diagnosed if the vein cannot be compressed with gentle pressure. Color Doppler ultrasound combines the findings of duplex ultrasound with color Doppler, which detects the blood flow and complete filling of the vein.
The studies by Heijboer and colleagues and Davidson and colleagues emphasize the need to interpret the test characteristics of noninvasive venous studies in the context of the setting in which they are done (1). Heijboer found excellent sensitivity but only moderate specificity with both the IPG and duplex ultrasound in symptomatic hospitalized patients. The 14% false-positive rate for US was much higher than studies done in outpatients (2) and may reflect the presence of other illnesses that lead to false positives. Davidson and colleagues found the sensitivity of color Doppler ultrasound was only 36% in asymptomatic high-risk patients having elective hip or knee replacement. This test may have had a lower sensitivity because the thrombi are frequently smaller and nonocclusive in asymptomatic patients receiving antithrombotic prophylaxis. Both studies confirm that each of these tests has a lower sensitivity in detecting distal DVT.
These and other studies suggest the following conclusions and diagnostic approach to DVT: 1) Duplex ultrasound and IPG have similar test characteristics. Color Doppler ultrasound has not been shown to be superior to duplex ultrasound alone. The test that should be used most often depends on the experience and expertise of the laboratory doing the study. 2) In symptomatic patients, if the test is positive, treat for DVT unless the patient is at high risk for bleeding complications from anticoagulation. Venography is indicated to confirm the diagnosis in those patients. If the initial test is negative, do serial tests to detect the migration of the clot from the distal to the proximal venous system. Withholding anticoagulation from patients with negative serial tests has been shown to be safe (3, 4). In asymptomatic high-risk patients, it is mandatory to use prophylactic therapy to reduce the risk for DVT and pulmonary embolism (5). Noninvasive studies are insensitive in this setting, and cost-effective screening strategies are not available at this time.
Jeffrey L. Carson, MD
University of Medicine and Dentistry ofRobert Wood Johnson Medical SchoolNew Brunswick, New Jersey, USA
4. Huisman MV, Büller HR, ten Cate JW, et al. Management of clinically suspected acute venous thrombosis in outpatients with serial impedance plethysmography in a community hospital setting. Arch Intern Med. 1989;149:511-3.