PSA is the best indicator we have so far of your risk of having prostate cancer. Prostate cancer disrupts the normal tissue structure, so more PSA leaks into the bloodstream and levels rise. The higher the PSA, the greater the chance of prostate cancer.

The median is the point where 50% men have a higher and 50% have a lower PSA (Table 1 below). The 95th percentile is the point at which only 5% are higher and some doctors will investigate further for PSAs over this level. However there is no single level above which you definitely have cancer and below which you don’t.

Men with small prostates will be at the lower end of the PSA range. Also, men who have had a trans-urethral resection of the prostate (TURP) for urinary symptoms will have had quite a bit (although not all) of their prostate tissue removed. A ‘normal’ PSA for them will be at the low end of the range.

The first step, if you have a high PSA, is to rule out other causes with other tests. One of these is called the ‘free to total’ PSA. Much of the PSA in the blood is bound to protein, including that produced by cancer cells. But men with benign prostate enlargement have higher levels of free (unbound) PSA and so a higher free to total ratio. If the total PSA level is abnormal, the free to total PSA ratio will give an idea of whether the rise is due to benign disease or cancer. Cancer is more likely if the free to total percentage is below 10%. This test is widely used throughout Australia.

The rate of change of PSA or PSA velocity is also used by some doctors to indicate a greater risk of prostate cancer. The higher the velocity, the greater the chance it is caused by cancer. A PSA velocity of 0.75 ng/mL/yr or more for a man with PSA at or above 4 is thought of as suspicious for cancer. However others suggest it is not more helpful than total PSA.

Table 1: PSA range (ng/mL)

Age (years)50th percentile (median)95th percentile