A chemiluminescent enzyme immunoassay (EIA) is quantitated by which of the following?

• A. the amount of light absorbed
• B. radiation detected on a gamma counter
• C. the intensity of emitted radiation
• D. the amount of light produced by the reactions

Answer: (D)

In a chemiluminescent immunoassay, the signal comes from light produced by the enzymatic reaction. The enzyme label catalyzes a substrate to emit photons, and the detector measures the light's intensity. That light output is proportional to how much analyte is present, allowing quantitation with a standard curve. Absorbance measurements aren’t used here because this method relies on light emission, not a color change. A gamma counter would detect radioactive emissions, which isn’t part of a chemiluminescent approach, and referring to emitted radiation can imply ionizing radiation rather than visible photons. So the quantitative readout is the amount of light produced by the reactions.