Clinical UM Guideline

This document addresses serum tumor marker cancer antigen carbohydrate antigen sialyl Lewis (CA 19-9) testing.

Note: Please see the following related documents for additional information:

• CG-LAB-32 Cancer Antigen 125 Testing
• CG-LAB-33 Carcinoembryonic Antigen Testing

Note: For a high-level overview of this document, please see “Summary for Members and Families” below. 

Medically Necessary:

1. CA 19-9 testing is considered medically necessary for either clinical scenario (A or B) and the following conditions (C):
   1. As part of initial evaluation for suspected or diagnosed disease; or
   2. To determine whether residual tumor exists post-surgical therapy;
      and
   3. Conditions:
      1. Ampullary adenocarcinoma; or
      2. Appendiceal adenocarcinoma; or
      3. Biliary tract cancers (gallbladder, cholangiocarcinoma); or
      4. Ovarian, primary peritoneal or fallopian tube cancer; or
      5. Pancreatic adenocarcinoma; or
      6. Small bowel adenocarcinoma (duodenum, jejunum, ileum).
          
2. CA 19-9 is considered medically necessary for the evaluation of occult primary cancer.
    
3. Repeat CA 19-9 testing* is considered medically necessary when used to:
   1. Monitor response to therapy; or
   2. Assess for recurrence when suggested by clinical factors.

*See Discussion/General Information section below for additional information on medical society guideline recommendations regarding the clinical appropriateness of testing frequency.

Not Medically Necessary:

CA 19-9 testing is considered not medically necessary when the criteria above are not met, including, but not limited to, as a screening test in an average risk individual.

This document describes clinical studies and expert recommendations, and explains whether cancer antigen 19-9 testing is clinically appropriate. The following summary does not replace the medical necessity criteria or other information in this document. The summary may not contain all of the relevant criteria or information. This summary is not medical advice. Please check with your healthcare provider for any advice about your health.

Key Information

Carbohydrate antigen 19-9 (CA 19-9) is a blood test that measures a substance that may be made by some cancer cells and normal cells. It is not used by itself to diagnose cancer. Instead, it may help healthcare providers evaluate certain cancers, check whether cancer remains after surgery, monitor how well treatment is working, or look for signs that cancer has come back. This document explains when CA 19-9 testing may be clinically appropriate and when it is not.

What the Studies Show

CA 19-9 is a protein that is normally found in small amounts in the body. It is made by cells that line the gallbladder, bile ducts, and pancreas. A high CA 19-9 level can be a sign of certain cancers, especially pancreatic or bile duct cancers. However, it can also be caused by non-cancer conditions, such as inflammation of the pancreas, liver disease, diabetes, or problems with the bile ducts. About 1 in 10 people do not make CA 19-9, so the test may not be helpful for them. Medical organizations, including the American Society of Clinical Oncology (ASCO) and the National Comprehensive Cancer Network^® (NCCN), recommend using CA 19-9 together with other tests for selected cancers. They do not recommend using CA 19-9 as a screening test for people at average risk who do not have symptoms.

When is CA 19-9 Testing Clinically Appropriate?

CA 19-9 testing may be appropriate in these situations:

• During the first evaluation of suspected or confirmed ampullary adenocarcinoma.
• During the first evaluation of suspected or confirmed appendiceal adenocarcinoma.
• During the first evaluation of suspected or confirmed biliary tract cancer, including gallbladder cancer or cholangiocarcinoma (CCA).
• During the first evaluation of suspected or confirmed ovarian, primary peritoneal, or fallopian tube cancer.
• During the first evaluation of suspected or confirmed pancreatic adenocarcinoma.
• During the first evaluation of suspected or confirmed small bowel adenocarcinoma of the duodenum, jejunum, or ileum.
• After surgery to help determine whether any tumor remains for the cancers listed above.
• To help evaluate occult primary cancer, which is cancer that has spread but the original location cannot be found.
• To monitor how well treatment is working.
• To help check whether cancer has returned when clinical findings suggest recurrence.

When is CA 19-9 Testing Not Clinically Appropriate?

CA 19-9 testing is not clinically appropriate in situations other than those listed above and as a screening test for people at average risk who do not have signs or symptoms of cancer.

Return to Description

The following codes for treatments and procedures applicable to this guideline are included below for informational purposes. Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy. Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.

When services are Medically Necessary:

When services are Not Medically Necessary:
For the procedure codes listed above for all other diagnoses not listed.

Summary

The protein carbohydrate antigen 19-9 (CA 19-9) is present in small amounts in healthy individuals. It is produced by the cells lining the ducts of the gallbladder, bile duct, and pancreas. Significantly elevated levels of CA 19-9 can indicate an underlying health issue, such as pancreatic cancer, gallbladder disease, or conditions related to the pancreas or bile duct. CA 19-9 testing has widely been utilized as a marker in prognosticating and managing pancreaticobiliary malignancies. The diagnostic utility of CA 19-9 is limited due to its relatively low sensitivity and specificity, but it has been used as part of a diagnostic evaluation under certain conditions.

Elevated levels of CA 19-9 can be associated with conditions other than malignancies, including pancreatitis, cholestasis, acute hepatitis, chronic liver disease, diabetes mellitus, interstitial pulmonary disease, and collagen vascular disease (Lim, 2022). While the exact mechanism is unknown, elevated serum CA 19-9 levels may be the result of overproduction caused by irritated bile duct cells and inflammatory proliferation of epithelial cells (Lim, 2022). Elevated levels may also be the result of normal production of sialyl Lewis a by non-malignant epithelial cells along with an occlusion of efferent ducts in the pancreas, leading to an accumulation of the biomarker and a backflow into the general circulation (Kannagi, 2007). Approximately 10% of the population do not express CA 19-9 which negatively affects the clinical utility of the test (Bowlus, 2023; Tsen, 2018).

Several medical societies and organizations, including but not limited to the American Society of Clinical Oncology (ASCO) and the National Comprehensive Cancer Network (NCCN), recommend CA 19-9 testing primarily for baseline evaluation, treatment response, and/or recurrence surveillance of select cancers. No professional society recommendations or guidelines currently recommend CA 19-9 be used as a cancer screening test in average risk, asymptomatic individuals.

Discussion

Ampullary Adenocarcinoma

Ampullary tumors arise from an area known as the Ampulla of Vater, which is composed of three distinct anatomical structures - the ampulla, the bile duct portion within the duodenum, and the pancreatic duct segment inside the duodenum. Individuals with ampullary adenocarcinoma often present with obstructive jaundice. According to the NCCN clinical practice guideline on ampullary adenocarcinoma (V2.2026), most individuals with ampullary adenocarcinoma present with elevated CA 19-9 levels.

In 2023, Lee and associates evaluated the relationship between the level of tumor marker CA 19-9 and prognosis to identify an optimal cutoff value for the marker to better evaluate an individual’s prognosis and to determine treatment strategies. Individuals who had undergone curative resection of ampullary cancer at a single institution (n=385) were included in the retrospective analysis. A cutoff value of 46 U/mL was found to be a significant diagnostic and prognostic factor. The use of CA 19-9 testing as a diagnostic preoperative element is useful as the diagnostic accuracy of endoscopic imaging is 67.3% and the diagnostic accuracy of the initial biopsy is 67.3-81.0%. The authors concluded that CA 19-9 can be used as an important reference point, along with other prognostic factors when deciding on treatment plans. Multiple studies have shown that elevated preoperative CA 19-9 levels have been associated with poorer outcomes, such as recurrence (Boyev, 2023; Klein, 2014; Ma, 2020; Okano, 2014; Todoroki, 2003).

The NCCN clinical practice guideline on ampullary adenocarcinoma (V2.2026) recommends obtaining a CA 19-9 level at presentation as high levels of CA 19-9 is considered a high-risk feature and may affect treatment decisions. CA 19-9 levels are considered a prognostic factor for survival and recurrence. Monitoring CA 19-9 levels is also recommended during the surveillance period every 3 to 6 months for 2 years, then every 6 to 12 months for up to 5 years as clinically indicated.

Appendiceal Adenocarcinoma

Primary appendiceal adenocarcinoma is a rare type of cancer. Primary appendiceal mucinous adenocarcinoma has an age-adjusted incidence of 0.12 per million per year (Fackche, 2021). Appendiceal cancer is frequently discovered incidentally during an appendectomy following clinical presentation of acute appendicitis. Management is based upon the classification, grade and stage of the neoplasm.

The use of tumor markers as a prognostic factor in individuals undergoing treatment has been evaluated. CA 19-9 and another tumor marker, carcinoembrionic antigen (CEA) have been determined to be independent prognostic markers regarding progression-free and overall survival or indicative of higher disease burden (Fackche, 2021; Fournier, 2017; Nizam, 2022; Wagner, 2013; and Yousef, 2024).

Pattalachinti (2026) reported on a single-center retrospective cohort study that suggests that perioperative serum tumor markers (CEA, CA 19-9, and carbohydrate antigen 125 [CA 125]) provide meaningful prognostic information in individuals with appendiceal adenocarcinoma undergoing cytoreductive surgery with or without hyperthermic intraperitoneal chemotherapy. Elevated preoperative tumor marker levels were associated with greater tumor burden, a lower likelihood of achieving complete cytoreduction, and shorter disease-free survival, while persistent postoperative tumor marker elevation was the strongest predictor of both disease recurrence and overall mortality. Conversely, normalization of tumor markers following complete cytoreduction was associated with significantly improved outcomes. These findings support the routine assessment of perioperative tumor markers for risk stratification and postoperative surveillance, although prospective multicenter studies are needed to determine how best to incorporate these biomarkers into clinical decision-making and whether tumor marker-guided management improves outcomes.

The NCCN clinical practice guideline on colon cancer (V2.2026) notes that for appendiceal adenocarcinoma, CA 19-9 and CEA levels should be taken at clinical presentation and abnormal measurements should be trended. These two tumor markers are used as prognostic indicators for individuals receiving cytoreductive surgery and hyperthermic intraperitoneal chemotherapy.

Biliary Tract Cancers

Biliary tract cancers consist of tumors which originate from the epithelial cells lining the biliary tract. Biliary tract cancers are a subgroup of cancers which fall under the spectrum of hepatobiliary cancers and include the intrahepatic bile duct, extrahepatic bile duct, gall bladder, and ampulla of Vater (Zamani, 2023).

Cholangiocarcinoma (CCA)

CCA, also known as bile duct cancer, can be categorized as intrahepatic or extrahepatic CCA. Intrahepatic CCA is the second most common type of primary liver tumor, making up 10 to 15% of these tumors (Mejia. 2020). Extrahepatic CCAs make up approximately one-third of biliary tract cancers. There are typically few or vague presenting symptoms associated with CCA, it is often diagnosed at the locally advanced or metastatic stage. Multiple studies have shown that monitoring CA 19-9 levels provides clinical utility when managing CCA (Cai, 2023; Hahn, 2020; Li, 2016; Mejia, 2020; Otto, 2024; Takahara, 2017; Yin, 2012).

Liang and colleagues (2015) published a systematic review and meta-analysis assessing the diagnostic performance of CA 19-9 for CCA. A total of 31 articles which included individuals with confirmed CCA who had CA 19-9 testing in the diagnostic phase (n=1264) and controls (n=2039) were evaluated. The type of controls within the studies varied and included normal controls, individuals with benign disease, primary sclerosing cholangitis and hepatocellular carcinoma (HCC). The researchers concluded that CA 19-9 was associated with a moderate diagnostic performance with an overall pooled sensitivity of 0.72 (0.70-0.75) and specificity of 0.84 (0.82-0.85).

The 2015 American Hepato-Pancreato-Biliary Association (AHPBA) expert consensus statement on intrahepatic CCA notes that the tumor markers CA 19-9 and CEA are not sufficiently sensitive enough to definitively rule out intrahepatic CCA when the levels are normal. However, discordance between tumor marker elevation and imaging results may suggest combined HCC and CCA. Tumor markers CA 19-9 and CEA are both indicated as part of the workup, CA 19-9 is elevated in approximately 50% of intrahepatic CCA cases and CEA is elevated in only 15-20% of cases.

In 2023, the American Association for the Study of Liver Diseases (AASLD) published a practice guideline addressing primary sclerosing cholangitis and CCA (Bowlus). While there are concerns about the specificity and sensitivity, an elevated CA 19-9 may be the only sign of CCA. A combination of CA 19-9 and other testing modalities (imaging or assessing for chromosomal aneuploidy) increases the sensitivity of testing. The AASLD includes the following guidance statements which address the role of CA 19-9 testing:

18. CCA and gallbladder carcinoma surveillance should be performed annually and include abdominal imaging, preferably by MRI/ MRCP with or without serum CA 19‐9. Surveillance is not recommended for patients with PSC under 18 years of age or with small‐duct PSC.

23. ERCP may be indicated for the evaluation of relevant strictures as well as new‐onset or worsening pruritus, unexplained weight loss, worsening serum liver test abnormalities, rising serum CA 19‐9, recurrent bacterial cholangitis, or progressive bile duct dilation. MRI/MRCP should be considered prior to ERCP to clarify the need for biliary intervention and guide the technical approach.

The NCCN clinical practice guideline on biliary tract cancers (V1.2026) recommend CA 19-9 as baseline workup tests, after initial hepatobiliary surgery or when a mass on imaging or jaundice is present, as well as for surveillance after resection, as clinically indicated. As CA 19-9 is not specific, CA 19-9 should be completed as part of a comprehensive baseline assessment and should not be used to confirm diagnosis.

While CA 19-9 is not indicated as a biomarker for individuals with HCC, an elevated CA 19-9 level in these individuals may be indicative of intrahepatic CCA or mixed HCC-CCA. In the NCCN clinical practice guideline on HCC (V1.2026), an elevated CA 19-9 level may warrant further investigation with core needle biopsy to rule out intrahepatic CCA or mixed HCC-CCA.

The measurement of CA 19-9 is also used in individuals with CCA who are undergoing evaluation for a liver transplant. An individual with hilar CCA with a malignant appearing cholangiography who is a liver transplant candidate may be eligible for a model for end-stage liver disease (MELD) or pediatric end-stage liver disease (PELD) score exception when there is a documented CA 19-9 greater than 100 U/mL in absence of cholangitis.

Gall Bladder

Gallbladder cancer is the most common type of biliary tract cancers, although it is considered to be rare with an estimated 12,610 new cases diagnosed and 4400 deaths in 2025 (American Cancer Society, 2025). Compared to hilar CCA, gallbladder cancer is associated with poorer outcomes.

The NCCN clinical practice guideline on biliary tract cancers (V1.2026) recommend CEA and CA 19-9 as part of the initial workup of gallbladder cancer and should be done in conjunction with imaging studies. The NCCN panel does not recommend CA 19-9 testing as a diagnostic test for potential gallbladder cancer as CA 19-9 levels can be elevated in individuals with jaundice from other causes. Subsequent CA 19-9 testing following treatment may be clinically indicated to monitor for disease relapse or progression.

Occult Primary Cancer (also known as Cancer of Unknown Primary origin [CUP])

Cancers are named based on their primary site regardless of where in the body they spread. The National Cancer Institute (NCI) defines occult primary cancer as a cancer in which the site of the original tumor cannot be found. When metastatic carcinoma is histologically confirmed in the absence of clinical, radiographic, or pathologic findings of the primary site, it is called occult primary cancer or CUP. CUP can sometimes be classified in categories that predict the primary site and target therapies to increase survival (Conner, 2015).

The NCCN occult primary cancer clinical practice guideline (V2.2026) identified CA 19-9 as a useful marker for CUP and may be useful in certain circumstances during the initial evaluation of a suspected metastatic malignancy. This test is not considered diagnostic and “caution must be exercised in their interpretation”.

Ovarian, primary peritoneal or fallopian tube cancer

Ovarian tumors consist of several histopathologic entities with epithelial ovarian cancer accounting for approximately 90% of cases. Epithelial cancer subtypes include endometrioid, carcinosarcoma, clear cell, mucinous, and borderline epithelial tumors. Elevated CA 19-9 levels are thought to be most associated with mucinous tumors, similar to mucinous tumors of the gastrointestinal tract. Approximately 12-15% of all ovarian tumors are categorized as primary mucinous tumors. Most primary mucinous tumors are benign (75%) with the rest classified as borderline (10%) or malignant (15%) (Cho, 2014).

Song and colleagues (2018) evaluated the diagnostic and prognostic value of CA 125 or CA 19-9 measurements in individuals with borderline ovarian tumors. Preoperative CA 125 and CA 19-9 values were used to evaluate whether elevated levels could assist in identifying advanced-stage disease, the prognostic significance of elevated levels and whether elevated levels could discriminate the histological type of tumor (serous and mucinous). CA 19-9 levels were elevated more often in mucinous tumors compared to serous tumors.

The NCCN clinical practice guideline on ovarian cancer (V4.2026) recommends CA 19-9 testing in individuals with mucinous ovarian neoplasms as part of the additional workup following diagnosis. While CA 125 is considered the primary tumor marker used to aid in the diagnosis and management of ovarian cancer, other tumor markers, such as CA 19-9 may provide useful information. Monitoring CA 19-9 levels may also be used to monitor for recurrence in individuals with mucinous tumors and in individuals with high pre-treatment CA 19-9 levels.

Pancreatic adenocarcinoma

CA 19-9 is recognized as a useful tumor marker in the management of pancreatic cancer and is “the only biomarker that is recommended for clinical use by pancreatic cancer guidelines” (Stoop, 2024). Tzeng and colleagues (2014) evaluated the relationship between CA 19-9 levels and clinical outcomes in 141 individuals with borderline resectable pancreatic cancer who were treated with neoadjuvant therapy. Individuals in this group were generally treated with chemoradiation prior to potential surgical resection. The evaluation included individuals who underwent resection and those who did not undergo resection. Normalization of CA 19-9 levels following treatment was associated with a longer median overall survival in both the resected and unresected group. Following resection, the positive predictive value of a CA 19-9 level decline was 70% and the negative predictive value of a CA 19-9 level increase was 88%. The authors noted:

In patients with borderline resectable PDAC (pancreatic ductal adenocarcinoma), the CA 19-9 changes observed over the course of NT appear to provide insight into tumour biology and treatment response, which, unlike in other solid tumours, cannot be evaluated radiographically.

Azizian and colleagues (2020) analyzed the accuracy of CA 19-9 in pancreatic cancer recurrence in individuals with PDAC who underwent curative surgical resection primarily followed by adjuvant chemotherapy. At a point of 2.45 times elevated CA 19-9 values, recurrence was detected with a 90% positive predictive value. The results indicated that elevated CA 19-9 levels were predictive of recurrence with high specificity and moderate sensitivity. The study suggested that an increase in these levels is an early, reliable sign of recurrence and can be used to make treatment decisions, and that regular testing may help improve accuracy.

Consistent findings have been reported through retrospective studies that acknowledge the role of CA 19-9 as a prognostic indicator and/or a monitoring mechanism for disease progression in individuals with pancreatic cancer (Newhook, 2023; Tsai, 2020; van Veldhuisen, 2018; Ye, 2020).

Schraps (2026) conducted a large tissue microarray study to comprehensively characterize CA 19-9 (sialyl Lewis^a) protein expression across a broad spectrum of human cancers and normal tissues and to evaluate its association with clinicopathologic features. There were 14,966 tumor specimens analyzed representing 134 tumor types and subtypes and 608 samples from 76 normal tissue types using standardized immunohistochemistry. Staining intensity and the percentage of positive tumor cells were categorized as negative, weak, moderate, or strong, and associations between CA 19-9 expression and clinicopathologic variables were examined for tumor types with available clinical data. CA 19-9 expression was detected in 79 of 134 tumor categories (59%), with 66 tumor types containing at least 1 strongly positive case, demonstrating that CA 19-9 expression extends well beyond pancreatic cancer. The highest expression occurred in biliopancreatic adenocarcinomas (84.4%-95.4%), including pancreatic ductal adenocarcinoma (95.4% positive; 83.0% strongly positive), gallbladder adenocarcinoma (84.4%), Klatskin tumors (82.9%), and CCA (81.2%). High expression was also observed in embryonal carcinoma of the testis (93.5%), endometrioid endometrial carcinoma (87.5%), pancreatic/ampullary adenocarcinoma (89.0%), and adenocarcinomas of the gastrointestinal tract, including esophageal adenocarcinoma (74.4%), gastric adenocarcinoma (54.7%-65.6%), and colorectal adenocarcinoma (65.1%). Conversely, CA 19-9 expression was absent or exceedingly rare in many mesenchymal tumors, lymphomas, melanomas, germ cell tumors (other than embryonal carcinoma), and neuroendocrine tumors. The associations between CA 19-9 expression and aggressive clinicopathologic features were tumor-type dependent, suggesting that the biologic role of CA 19-9 varies across malignancies. These findings support further investigation of CA 19-9 as a tumor-specific biomarker beyond pancreatic cancer, but prospective studies correlating tissue expression with serum CA 19-9 levels and clinical outcomes are needed before expanding its routine clinical application.

The American College of Radiology (ACR) appropriateness criteria document on resectable pancreatic cancer (2016) addresses the use of the CA 19-9 biomarker in the management of pancreatic adenocarcinoma.

The 2006 and 2020 ASCO recommendations for tumor marker use in gastrointestinal cancers do not recommend CA 19-9 testing alone to determine or assess the operability of individuals with pancreatic cancer. CA 19-9 was noted to be useful in conjunction with other testing in the management of locally advanced or metastatic pancreatic cancer and contain the following recommendations:

CA19-9 determinations by themselves cannot provide definitive evidence of disease recurrence without seeking confirmation with imaging studies for clinical findings and/or biopsy.
Present data are insufficient to recommend the routine use of serum CA19-9 levels alone for monitoring response to treatment. However, CA19-9 can be measured at the start of treatment for locally advanced metastatic disease and every one to three months during active treatment. If there is an elevation in serial CA19-9 determinations, this may be an indication of progressive disease and confirmation with other studies should be sought.

The NCCN clinical practice guideline on pancreatic adenocarcinoma (V2.2026) notes that CA 19-9 is the best validated and most clinically useful biomarker for the early detection and surveillance of pancreatic cancer. The NCCN recommends CA 19-9 testing “after neoadjuvant treatment, prior to surgery, following surgery immediately prior to administration of adjuvant therapy, and for surveillance.” The NCCN guideline further clarifies the recommendation noting:

The panel emphasizes the importance of obtaining a CA 19-9 measurement immediately before the therapeutic intervention to get an accurate baseline from which to follow response, for example, before and after neoadjuvant therapy in patients with borderline resectable tumors.

A markedly elevated CA 19-9 level is considered a high-risk feature along with other findings, such as equivocal or indeterminate imaging, borderline resectable disease, large primary tumors, or large regional lymph nodes. These features carry implications for prognosis and treatment. In cases where a person initially presents with an untreatable disease, a substantial reduction in CA 19-9 levels accompanied by clinical improvement could indicate a positive response to the neoadjuvant therapy. Such a response may warrant a reassessment of the individual's condition for potential treatment options. Following neoadjuvant therapy, disease progression is defined as a rising CA 19-9 level or an enlargement of the mass. In individuals undergoing resection, low postoperative levels or a serial decrease following surgery is considered a positive prognostic indicator. In individuals with advanced disease, pre-treatment CA 19-9 levels are considered an independent prognostic factor for survival. Serial CA 19-9 levels and computerized tomography scans for surveillance following resected disease is recommended every 3 to 6 months for 2 years.

Small Bowel Adenocarcinoma (duodenum jejunum and ileum)

The small intestine is the longest segment of mucosa in the gastrointestinal tract. Small bowel adenocarcinoma or cancer of the small intestine is an uncommon disease, representing only 6% of all new cancers diagnosed each year (Chen, 2018).

Altshuler and colleagues (2023) reported on the importance of CA 19-9 and CEA levels used as a prognostic indicator in individuals with duodenal adenocarcinoma. In 2022, Lim and associates identified the independent prognostic factors of individuals with resected non-ampullary duodenal adenocarcinomas (NADA) without metastasis at a tertiary cancer center. The median survival and disease-free survival in individuals with elevated CA 19-9 levels was significantly lower than in those with normal CA 19-9. In addition to CA 19-9 levels, age and symptoms at diagnosis were prognostic factors for survival following surgery. These studies along with other retrospective, single institution studies (Hirashita, 2018) provide some evidence, although limited, on the utility of CA 19-9.

The NCCN clinical practice guideline on small bowel adenocarcinoma (V2.2026) recommends CA 19-9 testing for the evaluation of jejunum, ileum, gastrointestinal, and metastatic adenocarcinoma. The surveillance protocol recommendations include CA 19-9 testing every 3-6 months for a period of 2 years, then every 6 months for a total of 5 years. While there is limited prospective data to clearly define the optimal management, Chen (2018) notes “Currently accepted treatment considerations are often generalized from large bowel and pancreatic-biliary cancers, due to some anatomic and clinical parallels”.

Other relevant information

United States Food and Drug Administration (FDA)-labeled indications exist for a number of assays for quantitative measurement of CA 19-9 in serum and plasma to aid in the management of individuals with cancer in whom changing concentrations of CA 19-9 are observed.

The Centers for Medicare & Medicaid Services (CMS) National Coverage Determination (NCD) 190.30 titled, Tumor Antigen by Immunoassay - CA 19-9, provides a framework for coverage consistent with demonstration of clinical utility. Available at: https://www.cms.gov/medicare-coverage-database/view/ncd.aspx?ncdid=142&ncdver=1&keyword=CA%2019-9&keywordType=starts&areaId=all&docType=NCA,CAL,NCD,MEDCAC,TA,MCD,6,3,5,1,F,P&contractOption=all&sortBy=relevance&bc=1.

Other Conditions

The 2006 ASCO recommendations for tumor marker use in gastrointestinal cancers does not recommend CA 19-9 testing in the diagnosis or management of colorectal cancer noting there is insufficient data to recommend CA 19-9 testing. The NCCN Clinical Practice Guideline on Colon Cancer (V2.2026) does not recommend CA 19-9 testing for any condition other than appendiceal adenocarcinoma. While elevated levels CA 19-9 may be found in the presence of other cancers in limited numbers, the studies have not shown clinical benefit evaluating CA 19-9 levels when diagnosing or managing these cancers. NCCN Clinical Practice Guidelines do not address CA 19-9 testing for other types of cancer not listed earlier.

Bąk and colleagues (2025) conducted a prospective observational study to evaluate whether CEA and CA 19-9 measured in serum and peritoneal lavage fluid could predict peritoneal dissemination in individuals with colorectal cancer. The study enrolled 89 individuals with histologically confirmed colorectal cancer who underwent surgery between May 2021 and May 2024. Serum CEA (sCEA) and CA 19-9 (sCA 19-9) were measured preoperatively, while peritoneal lavage fluid obtained intraoperatively was analyzed for peritoneal CEA (pCEA) and peritoneal CA 19-9 (pCA 19-9) concentrations. Cytologic examination of peritoneal lavage fluid was performed concurrently. The primary objective was to determine the association between tumor marker levels and peritoneal metastases, positive cytology, and clinicopathologic features. The cohort had a mean age of 69 years, with 46 men (51.7%) and 43 women (48.3%). Peritoneal carcinomatosis was identified intraoperatively in 11 individuals (12.4%), while 22 individuals (24.7%) had distant metastases. Only 1 individual (1.1%) had positive peritoneal cytology despite 5 cases requiring additional immunohistochemical evaluation because of suspicious cytologic findings. Elevated peritoneal tumor marker levels were associated with advanced tumor stage and macroscopic peritoneal metastases, supporting their potential role as adjunctive biomarkers for intraoperative risk stratification. However, because positive peritoneal cytology was identified in only 1 individual and the study included relatively few individuals with peritoneal carcinomatosis, larger multicenter studies are needed to validate these findings, determine their prognostic value, and establish whether routine measurement of peritoneal tumor markers improves management or outcomes in individuals with colorectal cancer.

Screening test

There is a lack of sensitivity and specificity associated with CA 19-9 testing which make this an inaccurate screening test (Zamani, 2023). Approximately 5-10% of the general population are “Lewis negative individuals” and do not express CA 19-9 (Azizian, 2020; Bowlus, 2023). Balaban and associates (2022) describe the physiology of these individuals:

Expression of CA 19-9 requires the presence of Lewis antigens A [Le(a+b-)] or B [Le(a-b+)], meaning that [Le(a-b-)] are theoretically non-producers of CA 19-9. Lewis negative individuals ([Le(a-b-)]) lack the enzyme α1-3,4 fucosyltransferase, which is required for CA 19-9 biosynthesis… As CA 19-9 secretion is dependent on the Lewis antigen expression, undetectable false negative results can occur in Lewis antigen-negative individuals, meaning [Le(a−b−)] non-expressors. This could represent a cause of delayed diagnosis in these patients and a pitfall in screening strategies based on CA 19-9.

Leseman (2026) conducted a systematic review and meta-analysis to evaluate whether serum CA 19-9 at the current guideline-recommended cutoff of ≥ 37 U/mL has limited value for detecting advanced intraductal papillary mucinous neoplasm, primarily because of its poor sensitivity (35%). Although elevated CA 19-9 levels are relatively specific and may increase suspicion for invasive carcinoma, normal CA 19-9 levels cannot reliably exclude either invasive carcinoma or high-grade dysplasia, particularly the latter, where sensitivity was only 9%. These findings indicate that CA 19-9 should not be used as a standalone screening or decision-making test but rather as one component of a comprehensive clinical assessment that incorporates imaging findings, cyst characteristics, and other risk factors. Future studies evaluating alternative CA 19-9 thresholds, longitudinal biomarker trends, or multimarker approaches may improve diagnostic accuracy.

The United States Preventive Services Task Force (USPSTF) recommends against screening for pancreatic cancer in asymptomatic adults. No NCCN guidelines recommend CA 19-9 testing to screen for the presence of cancer. The 2006 ASCO guidelines note that CA 19-9 is not recommended as a screening test for pancreatic cancer. It is widely accepted that CA 19-9 is ineffective as a screening tool (Ballehaninna, 2012; Henrikson, 2019; Kim, 2004; Lee, 2019; Lee, 2020).

Biomarker: A measurable indicator of a biological state or condition obtained from bodily fluids, such as blood or urine, or tissue samples. Biomarkers are used to diagnose diseases, monitor disease progression, predict disease prognosis, and track treatment response.

Diagnostic Test: A test conducted on individuals who exhibit signs, symptoms, or risk factors of a particular condition for the purpose of identifying the presence or absence of a specific disease or condition.

Disease progression: The advancement or worsening of a disease over time, characterized by increasing severity, expansion of disease involvement, deterioration in clinical signs or symptoms, loss of function, or objective evidence of worsening based on laboratory, imaging, or other diagnostic findings.

Hepatobiliary cancers: An aggressive grouping of cancers which originate in the liver. These cancers include hepatocellular carcinoma (HCC), gall bladder, and intrahepatic and extrahepatic CCA (bile ducts).

Mucinous cancers: A specific subtype of cancer characterized by the presence of extracellular mucin, a gel-like substance produced by some epithelial tissues and cells that may be found in cancers of the breast, colon, appendix, ovary, and lung, among others.

Prognostic Test: A test performed on individuals who have been diagnosed with a disease. Tests are used to predict the probable outcome or prognosis of the disease, provide information about the likelihood of disease progression, response to treatment, or overall survival.

Recurrence: Cancer that has returned post treatment, often undetected for a certain period of time. Recurrence can happen at the same location as the initial tumor or at a different site in the body.

Screening Test: A test administered to individuals when there are no signs or symptoms of a specific condition.

Surveillance: It is used to detect early signs of recurrence in diseases, particularly cancer, or to monitor individuals at an increased risk of a disease.

Tumor Marker: Any element found in or generated by cancer cells or other body cells in reaction to cancer or certain noncancerous conditions. This marker gives vital information about the cancer, including its aggressiveness, whether it is treatable with specific therapy, or its responsiveness to ongoing treatment.

Peer Reviewed Publications:

1. Altshuler E, Richhart R, King W, et al. Importance of carbohydrate antigen (CA 19-9) and carcinoembrionic antigen (CEA) in the prognosis of patients with duodenal adenocarcinoma: a retrospective single-institution cohort study. Oncotarget. 2023; 14:351-357.
2. Amoura Z, Duhaut P, Huong DL, et al. Tumor antigen markers for the detection of solid cancers in inflammatory myopathies. Cancer Epidemiol Biomarkers Prev. 2005; 14(5):1279-1282.
3. Azizian A, Rühlmann F, Krause T, et al. CA19-9 for detecting recurrence of pancreatic cancer. Sci Rep. 2020; 10(1):1332.
4. Bąk M, Wojciech M, Monczak R, et al. The significance of CEA and CA 19-9 levels in serum and peritoneal fluid in colorectal cancer patients in the context of peritoneal metastases and cytology results. Cancers (Basel). 2025; 17(16):2661.
5. Balaban DV, Marin FS, Manucu G, et al. Clinical characteristics and outcomes in carbohydrate antigen 19-9 negative pancreatic cancer. World J Clin Oncol. 2022; 13(7):630-640.
6. 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. J Gastrointest Oncol. 2012; 3(2):105-119.
7. Boyev A, Prakash LR, Chiang YJ, et al. Elevated CA 19-9 is associated with worse survival in patients with resected ampullary adenocarcinoma. Surg Oncol. 2023; 51:101994.
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4. Centers for Medicare and Medicaid Services (CMS). National Coverage Determination: tumor antigen by immunoassay - CA 19-9. NCD #190.30. Effective November 25, 2002. Available at: https://www.cms.gov/medicare-coverage-database/view/ncd.aspx?ncdid=142&ncdver=1&keyword=CA%2019-9&keywordType=starts&areaId=all&docType=NCA,CAL,NCD,MEDCAC,TA,MCD,6,3,5,1,F,P&contractOption=all&sortBy=relevance&bc=1. Accessed on July 30, 2026.
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   • Hepatocellular Carcinoma (V.1.2026). Revised March 10, 2026.
   • Occult Primary (Cancer of Unknown Primary [CUP]). (V.2.2026). Revised May 4, 2026.
   • Ovarian Cancer Including Fallopian Tube Cancer and Primary Peritoneal Cancer (V.4.2026). Revised April 10, 2026.
   • Pancreatic Adenocarcinoma (V.2.2026). Revised April 22, 2026.
   • Small Bowel Adenocarcinoma (V.2.2026). Revised April 7, 2026.
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    • ARCHITECT^® CA 19-9_XR Assay. K052000. October 25, 2005.
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CA 19-9
Cancer Antigen 19-9
Carbohydrate Antigen 19-9

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