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English Alf
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Date Joined Oct 2009
Total Posts : 2217
   Posted 2/10/2010 1:05 PM (GMT -6)   
I can't remember where I read about PSA half life so can someone help me. (even though I am now at a point where it no longer really matters)

Once you have no prostate then your PSA level in your blood will drop as your body continues to metabolises it but more is not being produced.

So how long does it take to go down?

I understood that it's half life was something like a week. ie
if your PSA was 10 before the op then it would be
5 one week after the op
2.5 after two weeks
1.25 after three weeks
0.625 after four weeks
0.312 after five weeks
0.16 after six weeks
0.08 after seven weeks
is that about right?

Alfred

James C.
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Date Joined Aug 2007
Total Posts : 4463
   Posted 2/10/2010 1:23 PM (GMT -6)   
More like a little less than 3 days or so, according to this Nature article:

www.nature.com/pcan/journal/v5/n2/fig_tab/4500567t2.html

Also, depends some on the individual and the race. In my case, mine dropped from 6.7 to .8 in 8 days. That's in line with the study results of less than 3 days.
James C. Age 62
Co-Moderator- Prostate Cancer Forum
4/07 PSA 7.6, referred to Urologist, recheck 6.7
7/07 Biopsy: 3 of 16 PCa, 5% involved, left lobe, GS 3/3=6
9/07 Nerve sparing open RRP 110gms.- Path Report: GS 3+3=6 Stg. pT2c, 110gms, margins clear
32 mts: PSA's: .04 each test since surgery, ED Continues-Bimix .3ml PRN or Trimix .15ml PRN

Post Edited (James C.) : 2/10/2010 11:28:53 AM (GMT-7)


Purgatory
Elite Member


Date Joined Oct 2008
Total Posts : 25393
   Posted 2/10/2010 1:57 PM (GMT -6)   
I always thought this provided a good answer:

cat.inist.fr/?aModele=afficheN&cpsidt=2536062

Post Edited By Moderator (James C.) : 2/10/2010 12:28:35 PM (GMT-7)


James C.
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Date Joined Aug 2007
Total Posts : 4463
   Posted 2/10/2010 2:33 PM (GMT -6)   
David, from that link, do I read it as saying that there may be accuracy problems with using free PSA as a marker, since it has such a short half-life, in the test tube as well as in the body? The way I read it, free PSA has such a short half life that the testing should be run immediately after it being drawn, within just a couple minutes, to be accurate. I am probably reading it wrong and the sample may be modified to extend the viable life of it.

From the report:

Conclusions. Unlike PSA, which has a half life of 2-3 days, the half-life of serum free PSA is 110 minutes (1.83 hours). This short half-life may have significant implications for the use of percentage of free PSA as a clinically useful tool in distinguishing patients with early, curable prostate cancer from men with benign prostatic hyperplasia (BPH) only.
James C. Age 62
Co-Moderator- Prostate Cancer Forum
4/07 PSA 7.6, referred to Urologist, recheck 6.7
7/07 Biopsy: 3 of 16 PCa, 5% involved, left lobe, GS 3/3=6
9/07 Nerve sparing open RRP 110gms.- Path Report: GS 3+3=6 Stg. pT2c, 110gms, margins clear
32 mts: PSA's: .04 each test since surgery, ED Continues-Bimix .3ml PRN or Trimix .15ml PRN


Casey59
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Date Joined Sep 2009
Total Posts : 3172
   Posted 2/10/2010 3:15 PM (GMT -6)   
James, the report posted by David speaks to the half-life of PSA (2-3 dayss) and free PSA (110 mins) in the bloodstream of a man after prostatectomy (60-minute intervals after surgery/removal). While in the bloodstream, the PSA and free PSA dissiminate into the body. I'm not sure if the kinetics are the same for a blood sample in a test tube, but I wouldn't assume it to be the same. I'm not enough of a blood specialist (what's the term for this; is it "hemoglobist"?) to know.

Possibly related, however, there is differences in "Specimen Stability" for blood draws for standard PSA test and the free PSA test.

From the Quest site, Specimen Stability for the standard PSA test is:
Room temperature: 7 days
Refrigerated: 14 days
Frozen: 1 year

For the free PSA test, it is:
Room temperature: 24 hours
Refrigerated: 24 hours
Frozen: 6 months

English Alf
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Date Joined Oct 2009
Total Posts : 2217
   Posted 2/10/2010 3:36 PM (GMT -6)   
Thanks for the replies

Does this mean it is important to know where the lab is in relation to the place where they take the blood or more relevantly when the test is done in relation to when they take the blood.

Say sample one is tested half a day after being taken and sample two taken three months later is tested half an hour after being taken could not an artificial result come back suggesting that the PSA had gone up between the two tests when it was actually the first sample had had longer to break down before it was analysed?

It makes me wonder why my hospital told me to have my blood taken at least a week before my appointment to give them enough time to test it!

Alfred

Casey59
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Date Joined Sep 2009
Total Posts : 3172
   Posted 2/10/2010 3:51 PM (GMT -6)   
I think your question is based on an assumption that the "half-life" studies of how quickly PSA disseminates in the bloodstream is directly related to changes of PSA in a test tube. I would repeat here my comment to James that I wouldn't assume it to be the same. Nor have I ever seen any studies related to PSA in a test tube. While I'm confident the Quest "Specimen Stability" would have been based on such a study, it's (probably) a really different dynamic than the dissimination of PSA into one's bloodstream.

While mistakes do happen, I believe that the trained technicians who draw the specimens know the proper handling techniques/requirements. I wouldn't worry excessively about how your samples are handled.

Your doctor probably wants you to get tested at least a week before your follow-up appointment with him so that your paperwork has time to get from the lab into his office and into your file so he doesn't have to go looking for it during your scheduled time.
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