Prostate cancer and the PSA test

A PSA blood test can be used to help diagnose prostate cancer at an early stage, before it causes symptoms and when it can be removed. The normal prostate gland makes a protein called prostate specific antigen (PSA). This protein helps to nourish sperm and only tiny amounts of PSA leech into the bloodstream. However, cancer cells in the prostate interfere with proper functioning and cause large amounts of PSA to enter the blood.

When high levels of PSA are detected in the bloodstream, this may indicate cancer. Other tests are needed to confirm the diagnosis, however, because an abnormal PSA test can have a number of non-cancer causes.

Normal PSA levels

The prostate slowly enlarges with age and the production of PSA will also rise. Generally, the healthy upper limits of PSA levels in the blood increase with age. One study suggests they may be between 2 and 5.6ng/ml (nanograms per millilitre) in men over 40 years. It is usually recommended that a PSA greater than 4ng/ml should be followed up with further tests.

Other factors that influence PSA levels

Prostate cancer is diagnosed using a range of tests, including the PSA blood test. The PSA blood test isn’t conclusive. It is possible, although rare, to have prostate cancer without raised PSA levels in the blood. A higher than normal PSA level doesn’t automatically indicate prostate cancer either. A high PSA level is due to cancer in around one in three cases.

PSA can be raised by other factors, including:

* Infection of the prostate (prostatitis)

* Benign prostatic enlargement (BPE).

For this reason, the PSA blood test isn’t used in isolation when checking for prostate cancer.

Tests – apart from PSA

Other diagnostic tests for prostate cancer include:

* Digital rectal examination (DRE) – the doctor feels for enlargement of the prostate gland or other changes.

* Biopsy – small samples of tissue are removed from the prostate and examined.

If cancer is diagnosed, further tests may be needed to determine the stage of progression of the cancer. These may include a bone scan, a computed tomography (CT) scan or a pelvic lymph node dissection.