CA 19-9 is a blood test used to determine the presence of CA 19-9 antigen. In patients with pancreatic or hepatobiliary cancer, this tumor marker is used in diagnosis, evaluation of a patient's response to treatment. CA19-9 represents the most important and basic carbohydrate tumor marker. Usually very little of CA 19.9 is detectable in the blood of normal individuals. Recently reports indicates that the serum CA19-9 level is frequently elevated in the serum of subjects with various gastrointestinal malignancies, such as pancreatic, colorectal, gastric and hepatic carcinomas. Together with CEA, elevated CA19-9 is suggestive of gallbladder neoplasm in the setting of inflammatory gallbladder disease. A persistently rising serum CA 19-9 value may be associated with progressive malignant disease and poor therapeutic response. A declining CA 19-9 value may be indicative of a favourable prognosis and good response to treatment.