[Theoretical and practical problems posed by the measurement of capillary filtration by radioactive tracers]

Screening for abnormal capillary filtration in the limbs with radioactive tracers requires the use of molecules of a known hydrodynamic radius. The molecule labeling should be obtained with a pure gamma-emitting radioactive atom, presenting a steady bond with the molecule, in vivo. Indium-111-labeled albumin appears to be the best tracer, and should be injected concurrently with the technetium 99m-labeled erythrocytes. The latter tracer permits assessing volume variations induced by the venous blood return block needed to obtain a capillary pressure increase. A qualitative estimation of lymphatic flow, and screening for abnormal permeability of the lymphatic vessels must be carried out as part of any capillary filtration study protocol.