The IHC test for Carcinoembryonic antigen is a laboratory technique used to detect the presence and localization of CEA protein in tissue sections using antigen–antibody reactions.

CEA is a glycoprotein normally present at very low levels in adult tissues but is often overexpressed in several epithelial malignancies, especially of the gastrointestinal tract.

In the IHC method, tissue samples (usually formalin-fixed, paraffin-embedded sections) are treated with specific anti-CEA antibodies. If CEA is present, the antibody binds to it, and this binding is visualized using a chromogenic reaction that produces a brown or red staining pattern under the microscope.