Diagnostic Methods Peripheral Vascular Disease

Platelets labeled with indium-I 11 have been used successfully as a marker of active thrombosis in man. To establish the diagnostic accuracy of platelet scintigraphy in comparison to contrast venography in the diagnosis of acute lower limb venous thrombosis, we evaluated 103 consecutive patients divided into two groups. Platelets were labeled by the indium-I 1 1 oxine method. Patients from group (n = 73, 56 had venograms) were asymptomatic and underwent platelet scintigraphy 1. 1 + 0.6 days (mean + 1 SD) after a major orthopedic procedure. Patients from group II (n = 30. all had venograms) were symptomatic and underwent platelet scintigraphy 1.2 + 1.7 days after venography. In group II, 15 patients with positive findings on contrast venography were treated with intravenous heparin; five others with positive venograms did not receive heparin until platelet scintigraphy was completed. Both platelet scintigraphy and contrast venography were evaluated by two blinded observers. Only studies with blinded agreement of both platelet scintigraphy and contrast venography were included in the analysis. Sensitivity and specificity of platelet scintigraphy for the whole limb were 93% and 97% in group I and 42% and 67% in group II. The lower sensitivity in group lI was most likely attributable to therapy with heparin. These results demonstrate that platelet scintigraphy, a test that permits imaging for up to five days after a single injection, correlates favorably with contrast venography in patients who have not received heparin and may be used as a surveillance test in high-risk patients. The role of platelet scintigraphy in acutely symptomatic patients requires further evaluation. Circulation 73, No. 4, 668-674, 1986. THE CLINICAL RECOGNITION of deep vein thrombosis is unreliable, lacking both sensitivity and specificity. ` In light of the potential hazards of anticoagulant therapy, an objective diagnosis of venous thrombosis is desirable before anticoagulant treatment is instituted. Currently, contrast venography is generally recognized as the reference diagnostic test. However, it may be uncomfortable for the acutely ill patient and is not suitable for repeated examinations. Complications are fortunately rare but include induced thromFrom the Yale University School of Medicine, New Haven, and the Veterans Administration Medical Center, West Haven, CT, and the University of Oklahoma and Veterans Administration Medical Center, Oklahoma City, OK. Supported by NIH Program Project Grant P0I HL 17812-07 and Veterans Administration Merit Review Grant (Dr. Ezekowitz). Dr. Sostman is a Clinical Investigator of the NHLBI (HL 01055). Address for correspondence: Michael D. Ezekowitz, M.D., Ph.D., Cardiology Section, Yale University School of Medicine, Fitkin 3, P.O. Box 3333, New Haven, CT 06510. Received Aug. 16, 1985; revision accepted Jan. 9, 1986. Presented in part at the 56th Scientific Session of the American Heart Association, Anaheim, November 1983. bosis and adverse effects of contrast material.4' The latter may be allergic, nephrotoxic, or hemodynamic. More importantly, even in the most experienced hands it is not always possible to visualize the entire venous system. Therefore efforts have been made to develop alternatives to venography. These include Doppler flow ultrasound6' 7 251-fibrinogen leg scanning,' 9 and the various plethysmographic techniques,10 of which impedance plethysmography is the most commonly used. There is no consensus as to which of these techniques should be employed uniformly either singly or in combination. The most thoroughly evaluated tests are impedance plethysmography and '251-fibrinogen leg scanning. In combination they have been proposed as an alternative to venography.5'" Fibrinogen scanning allows accurate recognition of thrombi in the calf, whereas impedance plethysmography is accurate above the knee. This approach, however, is not without difficulties. Fibrinogen scanning requires a delay of 24 hr before a definiCIRCULATION 668 by gest on Sptem er 6, 2017 http://ciajournals.org/ D ow nladed from DIAGNOSTIC METHODS-PERIPHERAL VASCULAR DISEASE tive diagnosis can be made. Because 1251 is not readily imaged, interpretation of studies in the presence of hematoma or thrombosis of nonvenous origin may be difficult. Impedance plethysmography may be limited by false-negative studies that occur in patients with good venous collaterals and by false-positive studies that occur in patients in heart failure or in those with a nonthrombotic or nonacute proximal occlusion. Increased muscle tension may provide interpretive difficulties. Optimally performed by experienced investigators, the combination of fibrinogen scanning and impedance plethysmography carries a sensitivity of 94% and a specificity of 91% in symptomatic patients.8 The role of indium1 1 1 (1 1'In) platelet scintigraphy in identifying thrombosis in man has recently been reviewed.'2' 13 Both animal and human studies have demonstrated its potential value for the diagnosis of deep vein thrombosis.'125 "'In has physical characteristics suitable for imaging that facilitates interpretation of studies. Theoretically, thrombi may be identified in any location. The physical half-life of the isotope (2.8 days) and the biological life of the injected platelet (8 to 10 days) permit imaging for at least 5 days after injection of the platelet suspension. Thus monitoring of natural history and therapeutic response is possible, as is surveillance of high-risk patients. The purpose of this study was to evaluate the accuracy of "'In platelet scintigraphy in comparison with the recognized standard of contrast venography in both acutely symptomatic and high-risk postoperative