Ligand Binding Assay

In medicine and pharmacology, a ligand binding assay (LBA) is a technique to identify the presence of a molecule and quantify it. There are numerous types of ligand binding assays, both radioactive and non-radioactive. As such, ligand binding assays are superset of radiobinding assays, which are the conceptual inverse of radioimmunoassays (RIA). Some newer types are called "mix-and-measure" assays because they do not require separation of bound from free ligand. Historically, LBA techniques were used extensively to quantify hormone or hormone receptor concentrations in plasma or in tissue. The ligand-binding assay methodology quantified the concentration of the hormone in the test material by comparing the effects of the test sample to the results of varying amounts of known protein (the ligand).

A prominent use was the test for classification of estrogen receptor status (ER) and progesterone receptor (PR) in breast tumors. The LBA was performed by homogenization of fresh or frozen tumor tissue, incubation of centrifuged cytosol with increasing quantities of radioactive estradiol-17β, followed by separation of unbound estradiol with dextran-coated charcoal (DCC) to quantify the concentration of high-affinity estrogen-binding sites (ER) using standard amounts of known protein.

It was replaced by immunohistochemistry (IHC), which may be superior to LBA for assessing estrogen receptor (ER) status in primary breast cancer because it is easier, safer, and less expensive, and has an equivalent or better ability to predict response to adjuvant endocrine therapy.