EIAs & ELISAs

96-Well Plate

EIA refers to Enzyme ImmunoAssay or Enzyme-Linked-ImmunoSorbent-Assay (ELISA). EIAs work in principal the same as RIAs with the immunogenic properties of the hormones used for quantification. Our laboratory uses the EIA method which employs antibody coating of the wells. Samples and standards are mixed with the enzyme-tagged hormone and applied to the wells where they attach to the antibody. After an incubation, the attached enzyme-tagged hormone is detected by adding a substrate indicator that produces a color reaction. The optical density of the enzyme is read by a spectrophotometer.

Our laboratory is currently using EIAs for measurement of estradiol, estrone-glucuronide, pregnanediol-glucuronide, estrone, progesterone, pregnanediol, testosterone, dihydrotestosterone, Interleukin-6, cross-linked N-telopeptides of type I collagen (NTx) and cortisol. The assays can be performed directly, such as the cortisol assay on tamarin urine, or can be performed after extraction such as rhesus monkey serum for progesterone. Column chromatography separation of steroids can also be performed prior to the EIA.

There are many advantages to using EIA systems over RIA. The sensitivity can be better than RIA. Correlations with RIA measurements are generally excellent. Since no radioactivity is required, the methods can be taught to a wide variety of people. The assays employed in our laboratory require short incubation times and the results of the assay are available in less than a day. EIA assays are considerably less expensive than RIAs.

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