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Re: PSA from different assays

Gregory,

The short answer to your question:

Can there be such a large difference between two different assays?

is YES, there can.

Back in the day when Don Cooley had a contact in the business, we were able to obtain some details of the test runs which were required to meet the so-called "Stanford protocol". This protocol, which no longer applies, was aimed at standardising the PSA results from different assays so that they were more directly comparable. (There were only three or four back then, compared to over twenty now) The range was amazing as were the adjustments required to get them within a cooeee of each other. Digging further, we found that no lab would guarantee the results within a range of 25% of the figure quoted in the test result, which represented the median.

So, in your case, this would mean that the 7.5 ng/ml result would be the median of a range between 5.62 ng/ml and 11.25 ng/ml and as the later number of 9.4 ng/ml is within this range, it might be said that there has been no signifcant change.

A number of people refused to believe that a test on which so much depended could be that inaccurate so we devised a number of experiments, one of which I participated in. I had a PSA test every day for 28 days, using the same lab and the same assay, with the blood taken at the same time of the day each day and trying as best I could to make sure I ate similar food, had the same amount of exercise etc. The results of this experiment are here PSA Experiment

Although, as crtics of the experiment were quick to point out, this was not a scientific study, but you might find it of intereest, especially seeing the increase of about 35% between days 15 and 18.

Bladder and prostate gland infections are notoriously difficult to deal with and the suggestion that ejacualte might show bacterial infeection seems worth pursuing. presumably the urine has already been checked?

Good luck
Terry in Australia

Re: PSA from different assays

Greg,
The simple solution is to just get your PSA checked every month for the next few months using the same lab. Changing the assay method probably doesn't make much difference anymore with the newer automated equipment that most labs use now but this way you will have eliminated that variable. You will now be using the same assay method and you can see how your PSA is changing and not worry so much about it's absolute value. You are starting from a very low risk situation so you've got the time to keep following your PSA and I'm sure your doctor will be happy to have your PSA done monthly now.

Re: PSA from different assays

I want to thank Frank and Terry for their thoughtful replies. The remaining question I have is as follows: How do I find the "real" PSA if I am unable to take the Cipro class of antibiotics which are the only prostate specific treatments for infection? Cipro has loweded my PSA several times in the past, but now I can't take it due to my Achilles Heel Tendonitis. Further biopsies are dangerous due to my e-coli infection from the last biopsy.

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