Immunoassay: A Medical Diagnostic Test

This article relates to Bad Blood

As reported in John Carreyrou's book Bad Blood: Secrets and Lies in a Silicon Valley Startup, Elizabeth Holmes's company Theranos produced a device that it claimed could run a medical diagnostic test called an immunoassay on a very small amount of blood.

An assay is a procedure for measuring the amount of, or presence of, a specific substance (an "analyte") in a larger body of material. Assays are used in many fields; for example, a geologist might assay a lump of ore to determine the amount of iron present in it. In medicine, an immunoassay is just one type of assay that might be run to assist in managing an individual's health. A biological sample is obtained from the subject, most often blood, which is then assayed for the presence of the substance being checked, such as a hormone or mineral. This diagnostic method is widely used in areas such as disease detection, monitoring of drug levels, and clinical trials of new medications.

The immunoassay technique was developed by Rosalyn Yalow (1921-2011) and Solomon Berson (1918-1972), researchers at the Veteran's Administration Hospital (VA) in the Bronx, New York. According to the Science History Institute, the pair teamed up in 1950 to study using radioactive-isotope materials to quantify minute amounts of a hormone in the blood of test subjects. Yalow was awarded the Nobel Prize in Physiology or Medicine in 1977 for her work, becoming just the second American woman to have won the award. Since Nobel Prizes are only awarded to the living, to honor her partner who was deceased by then, Yalow had her lab at the VA renamed for Berson so his name would be on every paper she published as long as she worked there.

The manner in which immunoassays are performed has changed over the decades, making them simpler and more cost-effective. These days radioactive isotopes have been replaced by a substance called acridinium ester, which generates a light-based reaction with the analyte which can then be measured. The tests have been refined to the point where they are highly specialized and specific, able to detect substances present in very low concentrations. They can also be run on a wide range of body fluids which, depending on the test, include blood, urine, nasal swabs, and samples from the patient's throat. The list of conditions now routinely detected by immunoassay includes influenza, Lyme disease, osteoporosis, strep, pneumonia, and pregnancy, among hundreds of other medical complaints.

Immunoassay technology in action

Filed under Medicine, Science and Tech

This "beyond the book article" relates to Bad Blood. It originally ran in December 2018 and has been updated for the January 2020 paperback edition. Go to magazine.

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