Highly iodinated fibrinogen: a new thrombus-localizing agent.

We have examined radioiodinated fibrinogen prepared at high levels of iodination as an agent for improved in vivo thrombus detection. Fibrinogen containing 25, 50, and 100 atoms of iodine per molecule is prepared by an electrolytic procedure and is compared with conventional radiolabeled fibrinogen (less than 0.5 iodine atom per molecule) prepared by the iodine monochloride method. The level of iodination has little effect on the isotopic clottability of the product, but its degree of aggregation and its rate of blood clearance in experimental animals is strongly dependent on iodination level. Isotopic thrombus: blood ratios obtained in recently induced thrombi with the 25 atom per molecule preparation average about 50:1, twice as high as the ratios obtained with conventionally labeled fibrinogen.