PSA and Digital Rectal Examination
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Prostate cancer is usually diagnosed two ways, either with a PSA elevation, which is a blood test that’s elevated, or on a digital rectal examination, an examination of the prostate.
PSA is a protein, it’s produced by the prostate and it seeps into the bloodstream.
It’s a simple blood test that’s taken.
If that level is elevated, in general, your chance of prostate cancer is high.1
We have various ways of using the PSA.
We use the absolute PSA level, and traditionally we used to use a level of four as the cut-off2.
More recently we’ve used age related levels, because your PSA goes up as you get older2.
There’s been data to show that we should use a new cut-off of 2.5, seen particularly in young men3, 4.
If their PSA is above 2.5, the risk of cancer is significantly elevated3.
Another, very important way of using PSA is the velocity of the rate of rise of PSA. PSA velocity is measurement of how fast PSA levels in the blood increase over time. A high PSA velocity may be a sign of prostate cancer and may help find fast-growing prostate cancers.2 If the PSA, even if it’s low, is rising reasonably quickly, the risk of cancer is elevated.
The last thing we use PSA for is the free to total ratio. PSA is a protein, it floats around the bloodstream, some of it’s free floating around, some is bound to a protein.
If we measure the amount that’s free floating around versus the total amount, we get a ratio test.
If you have a low ratio, your chance of prostate cancer is higher than if you have a high ratio.5
We also diagnose prostate cancer on a digital rectal examination, and that’s a very simple test.
Some people are quite concerned about it, but it’s very painless.
We examine the prostate and we feel the prostate, and generally the prostate’s usually the size of a walnut; it’s smooth, there’s no nodules, there’s no lumps or bumps, it feels like the tip of your nose.
If it feels firmer than that, then that can be a sign of possible prostate cancer.
The DRE can be a quick and helpful way to check if your prostate is showing any physical signs of cancer.6
So, the two ways are the blood test - the PSA, and the Digital Rectal Examination.
It’s important to do both, because 10% of cancers don’t actually produce PSA7, so it’s important to do both tests.
References
1. National Cancer Institute - https://www.cancer.gov/types/prostate/psa-fact-sheet#is-the-psa-test-recommended-for-prostate-cancer-screening2. National Cancer Institute - https://www.cancer.gov/types/prostate/psa-fact-sheet#what-is-a-normal-psa-test-result
3. National Library of Medicine - https://pubmed.ncbi.nlm.nih.gov/17681060/
4. Prevalence of prostate cancer among men with a prostate-specific antigen level < or =4.0 ng per milliliter https://pubmed.ncbi.nlm.nih.gov/15163773/
5. Prostate Cancer Foundation of Australia - https://www.prostate.org.au/testing-and-diagnosis/psa-testing/free-to-total-psa-testing/
6. Prostate Cancer Foundation of Australia - https://www.prostate.org.au/testing-and-diagnosis/diagnosis/digital-rectal-examination/
7. Association of very low prostate-specific antigen levels with increased cancer-specific death in men with high-grade prostate cancer - Brandon A. Mahal MD, Ayal A. Aizer MD, et al - https://acsjournals.onlinelibrary.wiley.com/doi/10.1002/cncr.29691