Abstract
For over 50 years, immunoassays have been extensively used to quantitate hormones in blood, other fluids and tissues. Each assay has its own sensitivity, specificity and other analytical components. Despite the differences between commercial products, these assays provide important clinical information about hormone levels in patients. However, inaccurate results can occur because of technical issues, as well as patient-specific factors that can interfere with immunoassay hormone measurements. The latter include excessive normal blood or serum components, the presence of cross-reacting substances, extremely high levels of hormones leading to the high-dose hook effect, and interference from a variety of endogenous factors such as human antibodies that interact with the assay components or high levels of biotin in the serum from exogenous ingestion. This article briefly reviews the sources and recognition of endogenous interference, and describes methods to determine the correct serum hormone concentration.