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Prostate specific antigen (PSA)

Written by Caidr's team of doctors and pharmacists based in UK | Updated: 06.04.2022 | 3 min read
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Prostate specific antigen (PSA) is a protein that is produced by the prostate gland, a walnut-sized gland located near the bladder in men. It’s normal to have some PSA in your blood. As you get older your prostate gets bigger and the amount of PSA released – measurable in a blood test – can slowly rise.

Prostate cancer can be one cause of a high PSA level, and early detection and treatment of this is beneficial. But it can also occur in other conditions. Therefore results are interpreted with caution, rather than giving a clear-cut answer.

If you have been diagnosed with prostate cancer, it may also be used to monitor your condition over time, and the success of any treatment.

Some prostate cancers do not cause a high PSA level, you may get a normal PSA, so it’s not always a good test for cancer or it’s treatment.

What affects the PSA?

A high PSA can be caused by a number of conditions affecting the prostate, such as prostate cancer, benign prostatic hypertrophy (BPH, where the prostate enlarges in non-cancerous growth) and prostatitis (where the prostate is inflamed, usually from an infection). Three out of every 4 men who get a positive PSA test do not have prostate cancer.

A urine infection can raise the PSA, so you’ll need to treat the infection first and then repeat the PSA after 6 weeks. Before your PSA test you should avoid vigorous exercise and ejaculation for 48 hours. You should also avoid anal stimulation for a week before the test. This includes sex or sex toys, and if your doctor has performed an intimate examination via the back passage to check the prostate.

If you’ve had any surgery to the bladder or prostate, a urinary catheter or a biopsy of the prostate, you will be advised to wait 6 weeks before having a PSA test.

It is important to note that medications called 5-alpha-reductase inhibitors such as finasteride or dutasteride, which help reduce the size of the prostate in BPH, can lower your PSA level and give you an incorrect result (a false negative).

Prostate cancer does not always cause the PSA level to rise – it will miss prostate cancer in nearly 1 in 7 men, because of a false negative.

Does high PSA mean I have prostate cancer?

The PSA test is not black-and-white - it's a test that if your level is high, it means you need further investigations. Many men with a raised PSA level don't have prostate cancer. This is called a false positive.

A normal PSA level does not rule out prostate cancer – if you have suspicious symptoms, this may warrant further investigations even with this so-called false negative.

Your doctor will ask about your symptoms, particularly in relation to passing urine, and about family history of prostate cancer or BPH. They will consider other risk factors, such as it you are African or Caribbean, obese or aged over 50 – all these can increase your risk of prostate cancer.

They will offer an intimate examination of your back passage, to feel the surface and size of your prostate. This gives further information into the cause of a high PSA or any symptoms.

Should I have a PSA test?

It can be a difficult decision because there is so much to consider and weigh up. These questions may help you make the decision:

  • Am I at increased risk of having prostate cancer? (If you are an older man, especially over 50, if you are Black, or if prostate cancer runs in your family)

  • Will I accept further investigations if my PSA is high?

  • Will a normal PSA reassure me?

  • If I was diagnosed with slow-growing prostate cancer that might never cause any problems, would I still want to have treatment, even though it could cause side effects? Or would I be comfortable having my cancer monitored instead?

If you are over 50, you can ask your doctor for a PSA blood test so long as you understand the risks and benefits.

It's a very personal decision whether to request the test or now, and if you still feel confused, you could talk all this through this with your GP.

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