What is the dx use of CA 19-9?

Major tumor marker in presence of jaundice (cholangitis) but can give false-positive, and negative BGs can give false negatives as well. Studies shown CA19-9 in pancreatic cancer in 85% (Cut off 37 U/ml), normalization of CA19-9 after resection and pt w/ CA19-9 above 90 didn't benefit from chemo