CEA (Carcinoembryonic Antigen) Test

CEA, or Carcinoembryonic Antigen, is a protein that's normally present at very low levels in adult blood but can rise significantly in certain cancers, most notably colorectal cancer, making it a useful tumor marker for monitoring rather than initial diagnosis.

This protein was originally identified in fetal digestive tissue, hence its name, and while healthy adults produce very small amounts, various cancers can cause tumor cells to release much larger quantities into the bloodstream.

CEA's main clinical value lies in monitoring patients already diagnosed with colorectal or certain other cancers — tracking levels before, during, and after treatment helps doctors assess how well therapy is working and watch for early signs that cancer might be returning.

It's not recommended as a general cancer screening test for people without a cancer diagnosis, since it lacks the sensitivity and specificity needed to reliably detect cancer in otherwise healthy people.