Unsatisfactory biologic behavior of ^*I-fibrinogen labeled by the chloramine-T method

The blood clearance of canine fibrinogen labeled with radioactive iodine by the chloramine-T method has been examined in dogs, and the distribution of ^*I studied with a gamma scintillation camera. The labeled fibrinogen prepared by this method is more than 85 per cent clottable, but less than 20 per cent of the label remains attached to the fibrinogen to trace its behavior in vivo. Some of the administered material, in the form of aggregated fibrinogen, is rapidly removed from the circulation by the liver and spleen. A considerable proportion of the label is released as free iodide and is taken up by the thyroid gland, stomach, and salivary glands and is also excreted in the urine. When fibrinogen is labeled by the iodine monochloride method, between 2 and 5 times as much label remains attached to the fibrinogen to trace its fate. These findings should discourage the use of the chloramine-T method of labeling fibrinogen.