Clinical Chemistry, Vol 21, 1113-1120, Copyright © 1975 by the American Association for Clinical Chemistry

Practical Applications of Radioimmunoassay Theory. A Simple Procedure Yielding Linear Calibration Curves

¹ Biochemical Procedures, Inc., North Hollywood, Calif. 91607.

Biochemical Procedures, 12020 Chandler Blvd., North Hollywood, Calif. 91607.

The fundamental equation describing radioimmunoassays under equilibrium conditions has been recast into a "working equation" in a form more directly applicable to the requirements of the analytical laboratory. Plotting total counts over counts bound vs. ligand concentration, which is conveniently linear over most of its course, is shown readily to yield quantitative data relative to binding site concentration and the equilibrium constant and to provide a means for deriving apparent labeled ligand concentration. Such data are helpful in establishing optimum assay conditions and can serve a continuing quality-control function. The working equation also characterizes the binder and tracer reagents used in the assay. The determination of working-equation parameters has been illustrated for the vitamin B₁₂ assay. Data are presented for seven different assay procedures, involving more than 600 calibration curves and 100 different lots of binding agent and tracer reagent, showing a Consistently High Correlation Coefficient (R> 0.990), between ligand concentration and the response variable.