Thanks a lot for your inputs everyone. They were insightful. I will post an update and will go with what the doctor suggests in my dad's case. I like the idea of getting it checked at the oncology lab where we visit the MO rather than going to our usual lab - but again the test method change could result in a different value and cause stress.
DjinTonic unfortunately my dad was diagnosed with metastatic prostate cancer with a single bone lesion and multiple lymph node mets in July 2019. So no RP for him. This test would mark his 8 month on Zytiga. Last PSA was indeed 0.001 ng/ml. Our lab in India gives result up to 3 decimals using CLIA ON CENTAUR (Earlier the same lab used CMIA on Architect but that also gave a result up to three decimals).
I sand corrected and remember you had previously mentioned this lower limit from Indian labs. As you mention, if you now use a lab/test with a higher lower limit, a result of, e.g., <0.01 gives you much less information. That reading would not tell you if your Dad's PSA is unchanged or increased, although it would still confirm a relatively very low value. Given our current virus situation, that would be acceptable, IMO.
Post Edited (DjinTonic) : 5/6/2020 6:45:27 AM (GMT-6)