CA 19-9 is a tumor marker that can be measured with a blood test. It is a substance that is released by some types of cancer cells into the blood. A high amount of CA 19-9 in the blood is most often caused by pancreatic cancer, but it can also be caused by other types of cancer or non-cancerous conditions such as infections in the liver, gallbladder, and pancreas. The normal range of CA 19-9 in a healthy person is less than 37 U/mL. However, a CA 19-9 level above 37 U/mL may indicate cancer of the pancreas, gallbladder, lung, or colon. It is important to note that higher levels of CA 19-9 may not necessarily mean that a person has cancer, and other tests may be needed to confirm a diagnosis.

According to one of the search results, a CA 19-9 serum level of less than 100 U/mL implies likely resectable disease, whereas levels above 100 U/mL may suggest unresectability or metastatic disease. However, it is important to note that CA 19-9 levels can vary depending on the patients age, gender, and stage of disease, and should be evaluated in conjunction with other blood tests, physical examinations, and diagnostic imaging tests for a more accurate assessment of the patients condition. Additionally, changes in CA 19-9 levels can help doctors monitor tumor growth, assess treatment response, and predict patient outcomes.