CA-19-9 is a cancer marker used to detect and monitor pancreatic, liver, and gallbladder cancers. It is a blood test that measures the levels of a protein called carbohydrate antigen 19-9 (CA-19-9) in the blood. The test is usually performed in a laboratory using a sample of the patients blood. The levels of CA-19-9 can be used to track the progression of the cancer and the effectiveness of treatment.