Hi Rose, the docs told Dad last week that the CA-19 is one of several diagnostic tools used to guage the status of the cancer. In Dad's case, following 3.5 mo. of Gemzar, his CA-19 went down from a ~28,000 to a ~6,000. This past week, it was back up to 9,000- along with an elevated bili levels (~22). While the scans did not show growth in the size of the tumor, the doc. did not interpret the results to be very positive- in that 2 out of 3 of the diagnostic measures did not come back in Dad's favor. I too had read that normal levels were somewhere in the 37-50 ballpark, so you can imagine our shock when we're talking tens of thousands!
I am certainly no authority on this source, I can only share what we've been told as part of the process.
Best to you.