Some important considerations for validation of ligand-binding assays

Calibration curves for ligand-binding assays (LBAs) are inherently non-linear and standard curve fitting algorithms require careful selection. Reference standards for macromolecule LBAs are more complex than are low-molecular-weight reference standards. Specificity of small molecule LBAs, and accuracy of reported study sample data are easier to assess by cross-validation with a chromatographic method than for macromolecule LBAs. Due to the lack of knowledge of the potential interference of unknown products of catabolism, proteolysis or biotransformation of macromolecules (particularly proteins) in LBAs for the parent molecule, the accuracy of reported concentrations and derived pharmacokinetic data for macromolecules, as determined by LBA, should be viewed with caution. In validation of LBAs, the total error and confidence interval approaches to assessment of the acceptability of an assay for routine implementation for the desired purpose should be given due consideration.