Other forms of PSA testing

New forms of the PSA blood test make it more accurate in diagnosing prostate cancer. One such test is the ‘free to total’ PSA test. In both healthy men and those with prostate cancer, the prostate specific antigen in the bloodstream latches onto protein. In men with benign prostatic enlargement, the prostate specific antigen tends to be free of protein.

The ‘free to total’ PSA test compares the amount of ‘bound’ to ‘unbound’ PSA to see whether the raised levels are caused by prostate cancer or benign disease. The probability of cancer is higher if the ‘free to total’ ratio is less than 20–25 per cent.

The rate of change of PSA (PSA velocity) can also be helpful in finding prostate cancer. In men with PSA above 4ng/ml, a velocity of greater than 0.75ng/ml/yr is thought to indicate a higher risk of cancer. This threshold may be lower in men with a PSA below 4ng/ml.

Monitoring cancer

After a diagnosis of cancer, regular PSA blood tests are also used to monitor the cancer activity in a man’s body. Generally, prostate cancer prompts higher and higher levels of blood-borne PSA as it grows. Regular blood tests can indicate whether the tumour is shrinking or enlarging and if the current treatment is working or not.

Where to get help

* Your doctor

* Urologist

* Cancer Council of Victoria, Information and Support Service Tel. 13 11 20

Things to remember

* A normal prostate gland secretes small amounts of a protein called prostate specific antigen (PSA) into the ejaculate and blood.

* Prostate cancer usually causes large amounts of PSA to enter the blood.

* The PSA blood test can detect prostate cancer at an early stage, before it causes symptoms and when it can be removed.

* An abnormal PSA test result can have a number of non-cancer causes. Other tests are needed to confirm the diagnosis.

* Prostate cancer testing and treatment is less likely to have a benefit in older men, particularly those over the age of 75 years.

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.