Review: Ultrasound has only moderate sensitivity in detecting asymptomatic deep venous thrombosis after orthopedic surgery
ACP J Club. 1995 May-June;122:77. doi:10.7326/ACPJC-1995-122-3-077
Wells PS, Lensing AW, Davidson BL, Prins MH, Hirsh J. Accuracy of ultrasound for the diagnosis of deep venous thrombosis in asymptomatic patients after orthopedic surgery. A meta-analysis. Ann Intern Med. 1995 Jan 1;122:47-53.
To evaluate, using meta-analysis, the accuracy of ultrasound for the diagnosis of deep venous thrombosis in asymptomatic patients after orthopedic surgery.
English-language studies were identified through MEDLINE (January 1982 to October 1993) using the Medical Subject Headings ultrasound, orthopedics, postoperative period, and thrombophlebitis. Additional studies were identified by scanning the bibliographies of retrieved articles, by independently searching recent issues of journals, and by using Current Contents.
Studies were selected if they evaluated the use of venous ultrasound imaging (B-mode, duplex, and color Doppler) compared with standard contrast venography for detecting deep venous thrombosis. Abstracts, early reports of studies later reported in full, and studies in which venography was not done in all patients were excluded. 2 reviewers independently evaluated the articles for methodologic standards.
Data pertaining to the accuracy of venous ultrasound were extracted. Studies were defined as level 1 if they had previously established objective criteria for venography and ultrasound, an independent blinded comparison of ultrasound with venography, and a prospective evaluation of consecutive patients. All other studies were defined as level 2. Sensitivity, specificity, and positive predictive values for venous thrombosis were calculated for the studies individually and for the results of the pooled level 1 and pooled level 2 studies.
16 of 30 identified studies met the selection criteria; 11 were level 1 and 5 were level 2. 7 studies evaluated B-mode ultrasonography, 7 evaluated duplex ultrasonography, and 2 evaluated color Doppler ultrasonography. In level 1 studies, ultrasonography detected 95 of 153 proximal thrombi, for a sensitivity of 62% (95% CI 54% to 70%). A falsely abnormal ultrasonographic result was found for 49 of 1463 venograms, for a specificity of 97% (CI 96% to 98%). The positive predictive value was 66% (95 of 144, CI 58% to 74%). Accuracy values for level 2 studies were higher; the sensitivity was 95% (CI 87% to 99%), the specificity was 100% (CI 99% to 100%), and the positive predictive value was 100% (CI 94% to 100%). Sensitivities, specificities, and likelihood ratios are shown in the Table.
Ultrasonography is only moderately sensitive for detecting proximal deep venous thrombosis in asymptomatic patients after orthopedic surgery.
Source of funding: S.R. McLaughlin Foundation.
For article reprint: Dr. P. Wells, Civic Parkdale Clinic, Room 455 Fourth Floor, 737 Parkdale Avenue, Ottawa, Ontario K1Y 1J8, Canada. FAX 613-761-4840.
Table. Ultrasound for the diagnosis of deep venous thrombosis in asymptomatic patients after orthopedic surgery (diagnostic standard is standard contrast venography)*
|Study quality||Sensitivity (95% CI)||Specificity (CI)||+LR||-LR|
|High (n = 11)||62% (54 to 70)||97% (96 to 98)||21||0.4|
|Lesser (n = 5)||95% (87 to 99)||100% (99 to 100)||Infinity||0.05|
*LRs defined in Glossary; LRs calculated from data in article.
The meta-analysis by Wells and colleagues focuses on an important clinical question. Its conclusions are probably valid because a thorough search for relevant articles was made, the validity of the included studies was appraised, and the results were similar from study to study.
From this study we learn, once again, that the operating characteristics of a diagnostic test are not the same in every clinical setting. In symptomatic outpatients with suspected deep venous thrombosis, real-time ultrasonography has high sensitivity and specificity (both > 90%) for clot in the thigh (1). The sensitivity of ultrasound for deep venous thrombosis in symptomatic inpatients may be slightly lower (89%) (2). Wells and colleagues have gathered convincing evidence that the sensitivity of ultrasound, with or without Doppler, is considerably lower when used as a screening test in asymptomatic patients after orthopedic surgery. This lower sensitivity might be explained by the clots being smaller, softer, and more easily compressible, and not completely occluding the vein. The clots may also be affected by prophylactic anticoagulation regimens. Specificity is high but the positive predictive value is low because of low disease prevalence. It should be noted that impedance plethysmography has an even lower sensitivity (24%) for thigh deep venous thrombosis in asymptomatic patients after hip surgery (3).
In asymptomatic patients after orthopedic surgery, the 2 best noninvasive tests for proximal deep venous thrombosis have limited accuracy. If an effective prophylactic anticoagulation regimen is being used, however, screening for deep venous thrombosis is unnecessary. If a diagnostic test for lower extremity deep venous thrombosis is desired (such as in the case of suspected pulmonary embolism), ultrasonography is most useful if positive. Venography should be used if the ultrasound is negative, if the physician is concerned about false positives, or if pelvic- or calf-vein thrombosis is sought.
John T. Philbrick, MD
University of VirginiaCharlottesville, Virginia, USA
3. Agnelli G, Cosmi B, Ranucci V, et al. Impedance plethysmography in the diagnosis of asymptomatic deep vein thrombosis in hip surgery. A venography-controlled study. Arch Intern Med. 1991;151:2167-71.