Immunoscintigraphic Detection of Venous Thrombosis of the Lower Extremities by Means of Human Antifibrin Monoclonal Antibodies Labeled with 111In

Abstract

A new monoclonal antibody spe cific for the beta-chain of human fi brin (C22A) and labeled with ¹¹¹In has been obtained and successfully used in rabbits and dogs for the in vivo de tection of venous thrombosis. Studies in humans are currently ongoing. In order to assess the diagnostic value of ¹¹¹In-antifibrin for the detection of ve nous thrombosis of the lower extrem ities, the authors investigated 25 consecutive patients. Ten patients had clinical and instrumental (con trast phlebography and duplex scan ning) evidence of acute deep venous thrombosis (DVT), 3 had a long standing DVT with relapsing epi sodes of swelling and pain, 5 had superficial venous thrombosis, and the remaining 7 had no signs of thrombosis at all. Twenty patients were being treated with heparin. All patients received ¹¹¹In-antifibrin at the dose of 74 MBq IV and were scanned with a large field of view gamma camera coupled with a high- energy, parallel-hole collimator at 30 minutes and three, six, and twenty- four hours postinjection. Only the persistence of an abnormal uptake at twenty-four hours confirmed by two observers at visual inspection was considered as positive. A positive result was obtained in 9 of 10 DVT patients (90% sensitivity) and in all SVT patients. The single DVT patient with a negative ¹¹¹ In- antifibrin test had the longest inter val between scintigraphy and onset of symptoms (fifty-five days). Thus, the age of thrombi represented a sub stantial limitation for the test. A false-positive result was obtained in a single SVT patient, in whom also a deep involvement, unconfirmed by phlebography, was suspected (91.6% specificity). The authors conclude that ¹¹¹In- antifibrin is a new diagnostic tool for studying deep venous thrombosis, which allows direct imaging of thrombi during their relatively early phase, with a high degree of sensitiv ity and specificity.