Biases in the assays of steroids and their binding proteins

Many immunoassays exhibit a bias. In such assays, the results are inaccurate, i.e. they deviate from the true value. The biases are mostly due to interfering compounds originating from the biological material assayed and/or from reagents. Sometimes systematic errors in calculation are also involved. The magnitude of the bias should be determined for every assay method, in order to make possible an assessment of reliability of the method. Biases frequently occur also in the measurements of steroid binding proteins, such as receptors, sex hormone binding globulin, corticosteroid binding globulin, etc. These biases are mostly due to the assumption that the measurements are performed under saturation conditions. These biases can be avoided by conducting the measurements at several concentrations of the ligand and by an appropriate correction for non-specific (low affinity) binding. In the assays of "free" steroids, biases are frequently encountered because of the disturbance of equilibrium in the course of the measurement proper. These biases can be minimized by a careful choice of experimental conditions.