CA 19-9 ( carbohydrate antigen 19‑9 or sialylated Lewis (a) antigen) is a type of mucin, a protein that is found on the surface of cells. CA 19-9 mucin is present in the fetal gastric, intestinal, and pancreatic epithelia, and it can be detected in lower amounts in adult tissues, including the liver, lungs, and pancreas .
Clinical significance:
CA19-9 is biomarker primarily used in diagnosis and monitoring of pancreatic cancer in addition to other diagnostic modalities. CA 19-9 assay values can assist in the differential diagnosis and monitoring of patients with pancreatic carcinoma with sensitivity 70% to 87%. Patients with serum CA19-9 levels >100 u/ml almost always have distal metastasis.
Interpretation:
For accurate and consistent serial testing, use the same assay method throughout treatment.
It is important to note that the CA 19-9 test is not a perfect test for pancreatic cancer. It can be elevated in other conditions, such as pancreatitis and cholangitis. Additionally, not all patients with pancreatic cancer have elevated CA 19-9 levels. Therefore, the CA 19-9 test should not be used as the only test to diagnose or monitor pancreatic cancer. It should be used in conjunction with other tests and imaging studies.
CA 19-9 Levels are Increased in :
pancreatic carcinoma, colorectal carcinoma, gastric carcinoma, hepatobiliary carcinoma ,Cirrhosis of liver, cholangitis ,pancreatitis, obstructive jaundice ,cystic fibrosis ,chronic liver disease.
Reference range of CA19.9 – < 39 U/ml
Limitations:
Patients known to be genotypically negative for Lewis blood group antigens will be unable to produce the CA 19-9 antigen even in the presence of malignant tissue.
Immunoassay may exhibit interference when the sample is collected from a person who is consuming a high dose of biotin (>5mg/day) Patients should be cautioned to stop biotin consumption at least 8 hours before collection of the sample.
In rare cases heterophile antibodies in serum can react with reagent immunoglobulin and cause interference in results, particularly seen in persons exposed to animals and animal serum products.
Additional information on CA19-9
The European Group of Tumor Markers (EGTM) advise that CA 19‑9 may be used as a diagnostic aid and for monitoring therapy in patients with pancreatic adenocarcinoma.
In pancreatic cancer, levels > 100 U/mL are highly suggestive of unresectablity or metastatic disease and levels < 100 U/mL imply a likely resectable disease2.
In colorectal cancer, CA 19-9 is considered an supplementary marker for tracking disease progression in patients when there is no elevation in CEA levels3.
References:
1.Wallach’s interpretation of diagnostics tests, 12th edition.
2.Ballehaninna UK, Chamberlain RS. The clinical utility of serum CA 19-9 in the diagnosis, prognosis and management of pancreatic adenocarcinoma: An evidence based appraisal. Journal of Gastrointestinal Oncology 2012;3(2):105-119
3.Stiksma J, Grootendorst DC, van den Linden PW. CA19-9 As a Marker in Addition to CEA to Monitor Colorectal Cancer. Clin Colorectal Cancer2014;13(4): 239-244.