What is CA 27.29?

CA 27.29 is a glycoprotein from the Mucin short variant S1, also known as polymorphic epithelial mucin (PEM) or epithelial membrane antigen (EMA), encoded by the MUC1 gene. Like other mucin glycoproteins, CA 27.29 plays a crucial role in the body’s defense system. Its extracellular domain features extensive O-linked glycosylation, where sugar molecules are attached to the oxygen atoms in threonine and serine residues. This structure allows CA 27.29 to prevent pathogens from reaching the cell surface by binding them to oligosaccharides in the extracellular domain.

Since the human body utilizes this defensive mechanism, CA 27.29 is commonly present in healthy individuals. However, elevated levels of CA 27.29 can indicate abnormal processes. The commonly accepted CA 27.29 normal range is below 38 units per milliliter (U/mL). Levels above this range can be seen in patients with various conditions, including certain types of cancers. In such cases, CA 27.29 levels are often correlated with the cancer stage, making this antigen a valuable tool for assessing cancer progression and monitoring its recurrence.¹

Health conditions that can elevate CA 27.29 levels

CA 27.29 levels often increase in individuals with metastatic breast cancer and various other oncological conditions, including cancers in:

• Ovaries;
• Uterus;
• Lungs;
• Colon;
• Stomach;
• Liver;
• Kidneys.

However, elevated levels of CA 27.29 can also indicate other health issues, such as ovarian cysts, endometriosis, and non-cancerous conditions affecting the breast, liver, and kidney. Certain infections may temporarily raise CA 27.29 levels. Additionally, during lactation and especially the first trimester of pregnancy, CA 27.29 levels can rise above normal even in healthy women.²

CA 27.29 blood test

The CA 27.29 test is a straightforward procedure that requires a blood serum – a liquid component of the blood. Samples are usually collected by drawing blood from a vein.

To assess CA 27.29 levels, the Siemens Advia Centaur CA27.29 Assay is used. This competitive immunoassay employs B27.29, a monoclonal antibody designed to detect an epitope (an antigen region that interacts with the receptors of the immune system) in the core tandem repeat domain of the MUC1 glycoprotein. This differs from the techniques used for detecting and measuring another mucin-based antigen, CA 15-3.³

The B27.29 antibody is noted for its higher specificity, which is crucial for reducing false positives that can arise when antibodies bind to similar epitopes on different molecules. However, since this antibody is patented by Siemens, the CA 27.29 test is less commonly used compared to the more broadly available, less specific CA 15-3 test.

To improve the accuracy of cancer evaluation, the CA 27.29 blood test is often performed alongside other examinations. For example, in the case of breast cancer, additional tests may include CA 15-3, a complete blood count (CBC), liver and kidney function tests, alkaline phosphatase, and blood calcium level measurements.⁴

References: 

1. “CA 27.29.” City of Hope.
   https://www.cancercenter.com/diagnosing-cancer/diagnostic-procedures/tumor-markers/ca-27-29
2. “CA 27-29 Tumor Marker.” Stanford Medicine. 
   https://stanfordhealthcare.org/medical-tests/t/tumor-markers/types/ca-27-29.html
3. Winston-McPherson GN, et. al “Interassay Comparison of the Tumor Markers CA125, CA15.3, and CA27.29.” The Journal of Applied Laboratory Medicine. 2017. 2(1):17–24.
   https://academic.oup.com/jalm/article/2/1/17/5587500

4. “CA 27.29.” Ulta Lab Tests.
   https://www.ultalabtests.com/test/ca-27-29#:~:text=Here%20are%20some%20tests%20commonly%20ordered%20alongside%20it%3A,Function%20Test%3A%20…%206%20Blood%20Calcium%20Levels%3A%20