Preparation of ligand-free human serum for radioimmunoassay by adsorption on activated charcoal.

I describe a convenient method for stripping hormones and other ligands from human serum. Formation of a serum/charcoal colloid is avoided by incubating serum on a limited surface area with activated charcoal, in a lateral oscillating shaker. Particle-free serum of negligible turbidity is obtained without ultracentrifugation by ejecting the centrifugate through a cellulose ester membrane. By this technique, more than 80% of thyrotropin, triiodothyronine, thyroxine, cortisol, insulin, digoxin, folate, estriol, or an ether derivative of testosterone is removed from serum. About 70% of follitropin and somatotropin are removed, as well as half the choriogonadotropin. Serum protein remains intact throughout the adsorption process.