Assay methods for performing non-competitive ligand-receptor assays, where said assays provide a sensible result when the target ligand identified by the assay is present at a concentration greater than a defined threshold concentration. The threshold concentration can be selected to be the upper limit of a normal range of values for a target ligand in a sample, so that an assay in accordance with the invention provides a sensible result only when the target ligand is present at elevated levels.