The blood test for PSA (prostate specific antigen) relates to a man's risk of prostate cancer. Unlike other cancers like breast and bowel, there is no routine screening programme for prostate cancer in the UK. This is because it’s not as straightforward as having a blood test and getting a black-and-white answer: it doesn’t tell you if you have prostate cancer or you don’t. Instead the NHS offers an informed choice programme. Men over 50 can ask their GP for a test (or tests every so often), but this is after discussion about how difficult the result is to interpret – PSA can be normal and you can still have prostate cancer, or it can be abnormal but you don’t have prostate cancer. A positive test usually means you need further investigations, and these can be uncomfortable and carry risks. Let’s talk you through what makes a good screening test, and how this can be applied to PSA screening.
The aim of screening is to pick up certain conditions or cancers before you have symptoms. Early diagnosis allows for early treatment, and hopefully less chance of risk to your health and ultimately to reduce your risk of dying early. The World Heatlh Organisation (WHO) sets the standard for what makes a good screening test – broadly they need to be reliable, accurate and have an obvious treatment path. The test needs be acceptable to the person being screened and relatively easy and inexpensive to do. And it needs to be a test for an important health condition. The PSA test as a screen falls short of some of these components, which is why it’s not offered in the UK routinely. Prostate cancer certainly is an important health condition – it's the most common cancer to affect men, with 1 in 6 being diagnosed in their lifetime. It has good prospects, in that it doesn’t usually spread to other parts of the body, and dying from prostate cancer is rare. The screening usually involves both a blood test to check the PSA level, and an intimate examination, called a digital rectal exam. This is where the surface and size of the prostate can be felt via the back passage. It can be uncomfortable and feel a bit embarrassing, but it’s not usually painful, and it’s over quite quickly.
A PSA test can help pick up prostate cancer before you have any symptoms and before it becomes widespread, giving a chance for earlier treatment. For those with an increased risk of prostate cancer, it can be helpful to check PSA levels, and perhaps make it a regular check. It can also be reassuring if it’s normal. Death from prostate cancer is rare, but screening does slightly reduce the risk of this.
There are several disadvantages, which is why it’s important to weigh these up in discussion with your doctor. A number of conditions besides prostate cancer can raise you PSA level. This is a so-called false positive result, where the raised PSA suggests cancer, where there is actually no cancer, and occurs to 3 out of every 4 men taking the test. This leads to significant anxiety and sometimes invasive investigations. These investigations can be uncomfortable, time-consuming, worrisome, and may risk side effects or damage to the prostate or nearby structures, such as taking a biopsy of prostate tissue. This may be worth the risk in cancer, but not if the tests are unnecessary in the first place. Similarly, it doesn’t differentiate between a slow-growing cancer that may never cause problems and may not shorten your life, compared with an aggressive cancer that needs radical treatment. This causes considerable anxiety for you and dilemmas about further invasive procedures that may be unnecessary. It can be falsely reassuring if you have prostate cancer but you have a normal PSA level. This means some cases would be missed by acting only on the PSA result, rather than considering any relevant symptoms, and this is called a false negative. The PSA test can miss nearly 1 in 7 cancers. Treatment involves either surgery or radiotherapy, both of which can cause significant side effects and risk of damage. This makes it important to ensure that treatment is not undertaken without good reason. It's ultimately a very personal decision, and after trying to reason through all of the pros and the cons, you may simply decide that if a test is available, you want to know the result either way. Or you may feel strongly that you'd rather not know, and if symptoms or signs come, you can deal with it then.