Review: 125I-Fibrinogen leg scanning is insensitive for detecting venous thrombosis
ACP J Club. 1993 Nov-Dec;119:80. doi:10.7326/ACPJC-1993-119-3-080
Lensing AW, Hirsh J. 125I-fibrinogen leg scanning: reassessment of its role for the diagnosis of venous thrombosis in post-operative patients. Thromb Haemost. 1993 Jan 11;69:2-7.
To determine, using meta-analysis, the sensitivity of 125I-fibrinogen leg scanning for the diagnosis of venous thrombosis in patients after operation.
Relevant reports were identified through a MEDLINE search for the years 1966 through 1991 and a review of recent journals using CurrentContents: Clinical Practice and biblioraphies of identified articles.
Studies in orthopedic or general surgical patients were selected if 125I-fibrinogen leg scanning was compared with venography in all patients (to assess accuracy) or in patients in whom 125I-fibrinogen leg scanning was abnormal (to assess the positive predictive value), and if ≥ 50 legs were included in the analysis. 15 studies met the selection criteria for accuracy, and 52 studies met the selection criteria for the positive predictive value assessment. Studies were considered to have level 1 evidence when criteria to define a normal and abnormal test result and venography were specified, when an independent and blind comparison of the test result and venography result was done, and when consecutive patients were included. All other reports were classified as level 2 studies.
Data pertaining to the number of patients included and study methods used and sufficient information to calculate sensitivity, specificity, and predictive values were extracted.
Of the 15 accuracy studies, 6 (all in orthopedic surgical patients) were ranked as level 1 and the remaining 9 (7 in orthopedic surgical patients) as level 2. In 6 level-1 studies, calf-vein thrombosis was detected in 380 legs by venography and by leg scanning in 210, for a sensitivity of 55% (95% CI 50% to 60%). Calf- or proximal-vein thrombosis was detected by venography in 511 legs and by leg scanning in 230, for a sensitivity of 45% (CI 41 % to 49%). Venographic results were normal in 2217 legs in which leg scanning was falsely positive in 176, for a specificity of 92% (CI 91 % to 93%). The positive and negative predictive values of leg scanning were 58% (CI 53% to 63%) and 89% (CI 87% to 90%), respectively. The sensitivity for isolated calf-vein thrombosis in 7 level-2 studies was 88%, and 82% for calf- or proximal-vein thrombosis, with a specificity of 79%. The positive predictive value of leg scanning among orthopedic surgical patients was 67% in level-1 predictive value studies (81% among general surgical patients) and 70% (80% among general surgical patients) in level-2 studies.
125I-fibrinogen leg scanning is an insensitive method for the screening of postoperative venous thrombosis in orthopedic and general surgical patients.
Sources of funding: Canadian Heart and Stroke Foundation and the Dutch Sandoz Research Foundation.
For article reprint: Dr. J. Hirsh, Hamilton Civic Hospitals Research Centre, Henderson General Division, 711 Concession Street, Hamilton, Ontario L8V 1C3, Canada. FAX 905-575-2646.
Venous thromboembolic events continue to be a substantial cause of morbidity and mortality after surgery. Because most patients who develop deep-vein thrombosis (DVT) after orthopedic surgery are asymptomatic, diagnostic screening modalities need to be both highly sensitive and specific. Radiocontrast venography, the gold standard for the diagnosis of DVT, is invasive and expensive and has potential side effects.
Noninvasive studies, such as 125I-fibrinogen leg scanning, impedence plethysmography, and duplex ultrasonography, have been widely used to diagnose DVT. The study of Lensing and Hirsh applied meta-analysis to evaluate 67 studies using 125I-fibrinogen leg scanning to diagnose DVT in orthopedic and general surgical patients. Overall, leg scanning was insensitive for the detection of DVT. The marked difference in sensitivity between level-1 (55%) and level-2 (88%) studies was probably caused by bias.
Impedence plethysmography and duplex ultrasonography have also been shown to be less sensitive in patients after orthopedic surgery (1-3), probably because of the higher occurrence of smaller and nonocclusive thrombi in these high-risk patients receiving DVT prophylactic therapy. Although duplex ultrasonography remains an excellent method for diagnosing proximal DVT in symptomatic outpatients, venography still remains the most accurate study in diagnosing asymptomatic high-risk postsurgical patients.
Clinical trials evaluating prophylactic antithrombotic therapies in high-risk patients should use venography to assess outcome measures. Studies evaluating such therapies using 125I-fibrinogen scanning must be interpreted with caution.
Scott A. Kolander, MD
Hahnemann University School of MedicinePhiladelphia, Pennsylvania, USA
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2. 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.
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