My husbands experience with the CA 19-9 has been similar to yours. It goes up and them comes back down. If his stent that he has in his bile duct gets sludge in blocked that will elevate the number. If his bilirubin goes up that usually means the CA 19-9 goes up as well. When they replace the stent it usually goes up a bit just from the Doctor going in to replace the stent.