Which assay is an example of a homogeneous immunoassay?

Which assay is an example of a homogeneous immunoassay?

• A. EMIT
• B. ELISA
• C. Western blot
• D. Immunofixation electrophoresis

Answer: (A)

In a homogeneous immunoassay, everything happens in solution without any separation step between bound and free components. EMIT fits this because it uses an enzyme-labeled antigen that competes with the patient’s antigen for binding to an antibody, and the readout is the enzymatic activity measured directly in the reaction mixture. The signal changes based on how much unlabeled antigen is present, so you get a quantitative result without washing away anything or immobilizing reagents. The other options rely on solid phases or separation steps: ELISA typically requires binding to a solid surface and washes to remove unbound components; Western blot involves transferring proteins to a membrane and detecting them; immunofixation electrophoresis uses electrophoretic separation followed by fixation and detection. That’s why they’re considered heterogeneous immunoassays.

In a homogeneous immunoassay, everything happens in solution without any separation step between bound and free components. EMIT fits this because it uses an enzyme-labeled antigen that competes with the patient’s antigen for binding to an antibody, and the readout is the enzymatic activity measured directly in the reaction mixture. The signal changes based on how much unlabeled antigen is present, so you get a quantitative result without washing away anything or immobilizing reagents.

The other options rely on solid phases or separation steps: ELISA typically requires binding to a solid surface and washes to remove unbound components; Western blot involves transferring proteins to a membrane and detecting them; immunofixation electrophoresis uses electrophoretic separation followed by fixation and detection. That’s why they’re considered heterogeneous immunoassays.