CA19-9 is a pancreatic cancer marker test that measures the level of a protein called Carbohydrate Antigen 19-9 (CA19-9) in the blood. CA19-9 is produced by certain types of pancreatic cancer cells, and its level in the blood can be used to monitor the progression of the disease in patients who have been diagnosed with pancreatic cancer. However, it is important to note that the CA19-9 test is not used for pancreatic cancer screening or diagnosis, and a high level of CA19-9 does not necessarily indicate the presence of pancreatic cancer. The test is typically used in conjunction with other diagnostic tools, such as CT scans, biopsies, and physical exams, to help doctors monitor the progression of pancreatic cancer and adjust treatment plans accordingly. In addition, the CA19-9 test may also be used to monitor the effectiveness of treatment and detect potential recurrence of pancreatic cancer.