Thoughts on CA19 behavior close to nadir

While there are "normal" ranges published for CA19-9 assays (which vary between manufacturers), my understanding is that these are based on some sort of 95% confidence interval for whatever group of normal non-cancerous people they used to establish the test basis. Individuals can have their baseline "normal" be different than a large population. Also since CA19-9 values can be affected by conditions other than cancer tumors, the data needs careful review prior to jumping to any conclusion . There is a recent article on use of CA19-9 as a leading indicator to CT scans for conditions where adenocarcinoma is known - "CA19-9 as a Dynamic Biomarker for Continuous Monitoring of Therapeutic Efficacy in Pancreatic Adenocarcinoma" https://www.mdpi.com/2072-6694/17/24/3902. In my wife's case her initial tumor showed almost no CA19-9 activity at all. The CA19-9 data have become useful only in the case of the metstatic recurrence. The attached picture shows the jump when metastases occurred in 2025 - subsequent chemo reduced the CA19-9 & the tumors. However we are now at 14 weeks of continuing small monotonically increasing CA19-9 values (red circled area) which seem to correlate with very early and marginal selected tumor nodule growth (and only at the limits of the CT resolution). We expect the next CT scan is 3 weeks to more clearly show tumor growth (and we'll adjust treatment). I think the punchline is to know each person has a somewhat unique CA19-9 profile at the low baseline values and to watch the trend lines as more informative at low values than an absolute number. Caveat: "Your mileage may vary."

@amiller7x7 thanks a lot this is very informative. On the last part of the graph, inside the green range I can see you had few upticks but trend in the first part was still going down before inverting. I wonder what was the amplitude of these upticks and how often you were testing. also out of curiosity why normal range was considered up to 54? wishing you good luck for next steps...

@peterello
Here's a plot of the 2025 data from CT scan in April (NED) to first routine CT scan (Jul 18) which occurred with metastatic recurrence on the CT scan. Our Oncology team relies more heavily on the CT scan for definitive diagnosis. This plot includes the most recent point showing an apparent acceleration in the rate of increase in CA19-9 values. We moved the CT scan to early next week and we expect to see tumor regrowth requiring a change in treatment. The small "upticks" were in the range of 1 to 10 units and tended to bounce around with no clear direction as opposed to the later data all of which were directionally increasing. As I mentioned, in our case, the trend lines were more important than any single data point. As to why the upper normal limit is 54, I have no direct knowledge of how that specific number was selected but it is the system used at the Fred Hutch Cancer Center in Seattle - I have to trust their calibration! :>)