How accurate is a PSA test in detecting Prostate Cancer?

A PSA blood test can detect early prostate cancer. However, cancer can be present even with a normal result. In this article, we will discuss the benefits and limitations of having a PSA test so you can make an informed decision

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What is PSA?

PSA stands for Prostate Specific Antigen, a protein produced primarily by the cells of the prostate gland. PSA is involved in helping sperm carry out its function and is primarily found in semen, but small amounts can also be detected in the blood. It’s normal to have some PSA in the blood, and this does vary with age, but elevated levels may be indicative of prostate cancer.

PSA levels can be measured by having a PSA blood test.

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About Prostate Cancer

Prostate cancer is the most common cancer in men with around 55,100 new cases in the UK every year and causes around 33 deaths every day. Certain factors can increase your risk of getting prostate cancer, which mainly include:

• age – prostate cancer is rare under the age of 50 and risk increases with age
• family history – if you have a close relative, for example, a brother or father, who has had prostate cancer
• ethnicity – the lifetime risk is 1 in 4 for men of black ethnic origin compared to 1 in 8 for white men

A PSA blood test can detect early prostate cancer…

A PSA blood test can detect early prostate cancer. If the cancer is caught earlier then treatment can be offered that may cure the cancer or extend life.

This is because prostate cancer can cause the architecture of the prostate to change causing more PSA to leak out in the blood. Therefore men with prostate cancer tend to have higher levels of PSA in their blood even without any noticeable symptoms.

However, cancer can be present without increased PSA levels. Around 15% of men with a normal PSA level (less than 3 nanograms/mL) may have prostate cancer, and 2% will have high-grade cancer.

Likewise, an elevated PSA result may not be due to prostate cancer. Instead, it might be caused by non-cancerous conditions such as an enlarged prostate, prostatitis, and even a urinary tract infection.

A PSA test therefore should not be used to diagnose prostate cancer but can be a useful tool for referring men for further testing.

What is an elevated PSA result?

Normal PSA levels vary with age. The UK government body NICE provides an agreed age-related threshold for determining what is above the normal range:

• 40 – 49 years: more than 2.5 ug/L
• 50 – 59 years: more than 3.5 ug/L
• 50 – 69 years: more than 4.5 ug/L
• 70 – 79 years: more than 6.5 ug/L

The above-normal levels for patients below 40 and above 79 years of age are based on clinical judgment.

There has been growing evidence to suggest measuring the PSA ratio in men with a PSA level between 4 ug/L and 10 ug/L. The PSA ratio is the ratio between a man’s Total PSA and his Free PSA level.

What can affect a PSA result?

PSA blood test results can be affected by certain activities or medications. Therefore, if any of the following applies, it’s important to wait to do a PSA test after the appropriate time has passed to ensure an accurate result:

• Vigorous exercise – vigorous exercise in the 48 hours before a PSA test can affect the result.
• Sexual activity – Any sexual activity that leads to ejaculation in the 48 hours before a PSA test can affect the result. Anal sex or having your prostate stimulated during sex, might raise your PSA level for around a week.
• Prostate biopsy or other tests or surgery – A biopsy or any tests or surgery on the bladder or prostate in the last six weeks before a PSA test, could lead to a falsely raised PSA level.
• Medicines – Some medicines used to treat an enlarged prostate or hair loss such as Finasteride (Proscar®) or Dutasteride (Avodart®), can reduce your PSA level and give a false test result.
• Urinary catheters – Having a catheter in the last six weeks after it has been inserted can affect a PSA test.

Summary

• A PSA blood test is good at detecting early-stage prostate cancer in some men
• PSA blood test is not completely accurate as it may miss around 15% of cases
• PSA levels can be affected by certain activities and medicines

References

[1] https://prostatecanceruk.org/prostate-information-and-support/prostate-tests/psa-blood-test

[2] https://www.gov.uk/government/publications/prostate-specific-antigen-testing-explanation-and-implementation/advising-well-men-about-the-psa-test-for-prostate-cancer-information-for-gps

[3] https://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/prostate-cancer

[4] https://cks.nice.org.uk/topics/prostate-cancer/diagnosis/assessment/#information-advice-on-psa-testing