Carcinoembryonic antigen, often referred to as CEA, is a type of protein that naturally occurs in the body. It belongs to a family of glycoproteins, which are proteins that have carbohydrate chains attached to them. This particular protein is typically found in certain tissues, and its presence can be measured through various laboratory tests.
Understanding Carcinoembryonic Antigen
Carcinoembryonic antigen (CEA) is a protein normally produced during the development of a fetus, particularly in the gastrointestinal tract. After birth, its production significantly decreases, and healthy adults typically maintain very low levels in their bloodstream. While its biological role in adults is not fully understood, its presence at elevated levels can sometimes indicate certain conditions. The protein is structurally a large glycoprotein. Its re-expression or increased production is sometimes associated with cellular changes.
Why CEA Levels Are Measured
Doctors measure CEA levels as a tumor marker to help manage specific cancers. This test is not used for initial cancer diagnosis or general population screening due to its limitations. Instead, it monitors patients already diagnosed with cancers, such as colorectal, lung, breast, ovarian, or pancreatic cancer.
CEA levels help healthcare providers track the effectiveness of ongoing cancer treatments, such as chemotherapy or radiation therapy. A decrease in CEA levels during treatment can suggest that the therapy is working to reduce the tumor burden. Conversely, rising levels after treatment might indicate that the cancer has returned or progressed. This marker can also provide some insight into a patient’s prognosis, as persistently high or increasing levels may suggest a more aggressive disease course.
How CEA Testing is Performed
Measuring carcinoembryonic antigen levels involves a routine medical procedure. The test requires a blood sample, which is typically drawn from a vein in the patient’s arm. A healthcare professional collects the sample using a sterile needle and a collection tube.
Once collected, the blood sample is sent to a laboratory for analysis. In the lab, specialized techniques are used to quantify the amount of CEA present in the blood serum. Generally, no special preparation, such as fasting, is required before undergoing a CEA blood test.
Interpreting CEA Test Results and Their Limitations
Interpreting carcinoembryonic antigen test results requires careful consideration by a healthcare professional. For non-smokers, normal CEA levels are typically below 2.5 to 3 nanograms per milliliter (ng/mL), though some laboratories may consider up to 5 ng/mL as normal. Smokers often have slightly higher baseline levels, sometimes up to 5 ng/mL or even 10 ng/mL, due to nicotine’s effects on the body. Elevated CEA levels can suggest cancer progression, recurrence after treatment, or the presence of a non-cancerous condition.
Despite its utility in monitoring, CEA is not a definitive diagnostic tool for cancer. Many individuals with cancer, particularly in the early stages, may not have elevated CEA levels, meaning a normal result does not rule out the presence of malignancy. Conversely, elevated CEA levels can occur due to various non-cancerous conditions, including inflammation, infections, liver diseases like cirrhosis, inflammatory bowel disease, pancreatitis, and benign breast conditions.
Healthcare professionals must interpret CEA results within the broader context of a patient’s comprehensive medical history, physical examination findings, and the results of other diagnostic tests, such as imaging scans or biopsies.