Immunoscintigraphy of venous thrombi: Clinical effectiveness of a new antifibrin D-dimer monoclonal antibody

Safety and thrombus imaging capabilities of the Tc-99m-labeled form of a ne w F(ab')(2) monoclonal antibody (MoAb) against fragment D dimers from cross -linked human fibrin, previously shown to be effective labeled to I-131 in detecting venous thrombi in the rabbit, were investigated. Sixteen patients (seven men, mean age: 60 +/- 7 years) with deep (n = three ) and superficial (n = 13) venous thromboses of the lower limbs documented at echo-Doppler study underwent, 24 hours before saphenous vein stripping, a scintigraphic study after IV injection of the Tc-99m-MoAb (1,129 +/- 275 MBq/mL), acquiring dynamic images, as well as early and delayed static imag es of lower limbs. Tracer activity was compared in normal and pathologic ar eas. At the operation, vessel wall including the thrombotic lesion was isol ated, weighed, and counted. Blood radioactivity and MoAb concentration were also measured. No adverse reaction was observed after MoAb administration. Thrombus site a ppeared as a focal area (hot spot) of asymmetrically increased tracer uptak e, already detectable at early images in all patients. All thrombi detected at echo-Doppler study (n = 25) were confirmed at scintigraphic study, whic h showed four additional hot spats subsequently confirmed to represent thro mbi at operation. Average percent ratio between pathologic and normal regio ns was 1.51 +/- 1.34 (p < 0.05) at time-activity curves, 2.27 +/- 1.1 (p < 0.05) at early static images, and 2.15 +/- 1.2 (p < 0.05) at delayed images , respectively. Thrombus-to-blood uptake ratio was 4.3 +/- 0.9 (p < 0.01). The F(ab')(2) MoAb proved to be safe, and low levels of antimouse antibodie s were detected in response, although further studies are needed to assess tolerance and effectiveness in case of a second administration in the same patient. The Tc-99m-labeled MoAb was very effective in identifying venous t hromboses both at deep and superficial localizations, although its sensitiv ity and specificity need be evaluated in a more numerous group, including a lso patients with different and clinically more relevant localizations, suc h as caval thromboses. However, the possibility of obtaining high-quality i mages within 4 hours of MoAb administration is clinically relevant, and car ries also therapeutic implications, especially in pulmonary thromboembolism .