CaPCA said...
...I have posted on this before, and I am curious as to why the LOWEST level for post-prostatectomy PSA is always the one after surgery... What I have NEVER seen is a trend DOWN from the PSA level after surgery... What makes the post-surgery level apparently the absolute lowest level that a man can expect during recovery?
CaPCA,
There absolutely IS a trend downward of PSA after surgery, down to it's lowest point. The understanding of this is rooted in the half-life decay of PSA in one's bloodstream, and this is the fundamental basis of why surgeons tell patients to wait 8-12 weeks or so after surgery before getting their first (lowest) PSA test.
Basic review: The prostate is the primary source of PSA. PSA enters the blood serum from the prostate and reaches an equilibrium as it circulates throughout the veins of the body (which is why a blood draw from the arm gives a reliable PSA measurement).
Over time, the PSA dissipates out of the blood, but is replaced by the steady, on-going supply of the prostate. PSA has a dissipation half-life of 2-3 days in the body.
If, however, the prostate is removed, then the supply of new PSA is abruptly stopped. However, the PSA already in the blood right after the prostate is removed does not immediately drop to zero; rather, it dissipates as per normal, but is not replaced by a new supply of PSA.
The amount of PSA in the blood 2-3 days after surgery is about half the amount that it was before surgery (half-life). 2-3 days after that, it is about half-again as much. The amount of PSA in the blood trends downward (your question, CaPCA) in a (nearly) asymptotical decay curve...that is until it levels out with the very low levels of PSA from other sources (PSA is never "zero" in a living, breathing person).
I also posted a detailed example of this just about 2 weeks ago, on 1/27/2010. If the explanation above is difficult to understand, maybe the example in this other thread will make it more clear. Here's the link (my example is about the 16th posting down): https://www.healingwell.com/community/default.aspx?m=1703015&f=35&p=1
-------------------------------------
I should add in this follow up edit that once the PSA drops down to it's "lowest point", in an ultra-sensitive PSA test there may be some slight variation up/down by some small number of hundredths which is considered normal variation of the test results. This is beyond the main gist of CaPCA's question, but wanted to head-off anyone challenging the notion of the "lowest point" based on this slight variation once the post-surgical half-life decay has taken place.
Post Edited (Casey59) : 2/10/2010 6:07:06 AM (GMT-7)