Serum
ug/L
0- 3.8 ug/L
CEA is a large family of 36 different, but related, glycoproteins, which are part of the immunoglobulin superfamily. The human CEA gene family is clustered on chromosome 19q and comprises 29 genes. Seven of these 29 genes code for CEA glycoproteins. CEA molecules exhibit considerable heterogeneity due to variation in carbohydrate side chains.
CEA is present in the gastrointestinal tract during fetal life and occurs at low concentrations in adults. CEA was first reported to be quite specific for tumors of the GI tract, but further investigations demonstrated elevations in several other malignant and benign diseases. Elevated CEA levels are suggestive, but not diagnostic of cancer, since elevated levels also occur in a variety of benign conditions:
Serum CEA is ordered most often for patients with colorectal cancer. Numerous studies have demonstrated that:
Serum CEA is not sensitive enough to be used as a screening test for colorectal cancer. The goal of colorectal cancer screening should be to detect disease at either stage I (Duke’s A) or II (Duke’s B). Using a cutoff of 2.5 ug/L, CEA is elevated in only 30% of patients with stage I and II cancer. CEA levels cannot distinguish locally invasive premalignant colonic polyps from benign polyps.
Duke’s staging system has been the gold standard for predicting outcome in patients with newly diagnosed colorectal cancer. Additional prognostic factors are particularly needed for patients with stage II (Duke’s B, node-negative) colorectal cancer because 40 to 50% of these patients have aggressive disease and might benefit from adjuvant chemotherapy. The majority of studies suggest that preoperative CEA levels can provide prognostic data in patients with stage II colorectal cancer. High levels are associated with more aggressive disease.
The circulatory half-life of CEA is ~7 days. After successful surgical resection of colorectal cancer, an increased CEA concentration should return to normal within 4 to 6 weeks. Failure of an increased preoperative level to decrease in to the normal range within 6 weeks of surgery frequently is associated with recurrent disease.
The use of serial CEA levels to follow patients who have no evidence of disease after primary therapy is more controversial. Serial CEA determinations are most useful in detecting liver metastasis. Sensitivity and specificity are approximately 90%. Hepatic resection for isolated liver metastases achieves long-term survival in 20 to 50% of patients and may be the only curative therapy for metastatic colorectal cancer. Because of this success, the American Society of Clinical Oncology (ASCO) recommends CEA monitoring only in those patients with stage II and III (Duke’s C) disease who are willing and able to undergo a hepatic resection for metastatic disease. For this subset, CEA monitoring is recommended every 2 to 3 months for at least 2 years after diagnosis.
CEA has a much lower sensitivity and specificity for detection of local recurrence after successful primary therapy. A compilation of data from several studies suggests that elevations in CEA correlate with relapse only 40% of the time. That means that 60% of the time, CEA levels were falsely elevated. However, CEA does appear to be superior to endoscopy, computerized tomograpy and ultrasound in diagnosing local recurrences. Monitoring with CEA can detect recurrent colorectal cancer with an average lead-time of 5 months (range, 4 to 10 months) before these other modalities.
A difference of >20% between two CEA measurements is considered medically significant.
Local test
1 day
Can be added on to an existing request up to 4 days following sample receipt
12 days
Specimen Labelling Procedure
8210
