@jc76 Thanks. One thing that helped me dive deeper was my brother who's a 30 year PCa survivor of both surgery and extensive radiation just coincidentally happened to get his annual PSA at the same time as my 3 month psa from the same lab. Both of our orders were for just the "standard" psa (not the ultra sensitive one). My brothers psa has been undetectable for decades, and he also got a .004 just like I did. That led me to check on the machines used. When checking on the machines, it appeared that the specific calibration for a given machine will affect where the "floor" is for a given machine. Since I had my brothers .004 from the same lab within a day or 2 of mine, I surmised that .004 was "undectable" for (what I strongly suspect) was the same exact machine calibrated to that level. I don't know, but I suspect even though my lab order was for a "standard" psa, they used an ultra sensitive machine for their own convenience at the 3 month check. At my 6 month check for a "standard" psa, for whatever reason they used a less sensitive machine. I could well be wrong, but it sure fits the data I saw on the 2 lab reports. Meanwhile, at my 3 month visit with the staff Mayo urologist she said < .1 is what they're looking for. I have my 6 month visit later this morning so I'll see what she says this morning. So far, I'm pretty relaxed about it but I'll report back after my televisit in 5 hours.