In Vitro Radioisotopic Methods for Clinical Evaluation of Vitamin B₁₂ and Folic Acid Metabolism

Abstract

Many important physiologic processes are mediated by substances present in concentrations too low to be measured with instrumentation dependent on colorimetric or fluorometric reaction systems. Consequently, the assay procedures for many hormones, enzymes, metabolic substrates and vitamins was dependent for many years on biological activity where sensitivity, if not precision, was greater. However, with the availability of radioactive isotopes which could be incorporated into these substances, a significant advance had been made because they could now be monitored at lower and more physiologic concentrations. Coupled with the availability of radioactive labels was the development of the competitive radioimmunoassay for insulin by Yalow and Berson (1) which probably was the singular most important advance in the field of biomedical measurement. This technique, first exploited for the measurement of insulin, has now been extended for the measurement of other hormones, both peptide and non-peptide, other types of proteins, vitamins and drugs, using, in addition to specific antibodies, other macromolecular binding ligands or receptor sites obtained from tissues or biological fluids.