PSA: Is it a good prostate cancer marker?

Prostate specific antigen (PSA) is a protein produced by cells in the prostate glands. Thus only male has PSA. PSA has been widely used as a screening tool for prostate cancer.

   Location of prostate gland

It is still controversial whether PSA is suitable to be used to screen for prostate cancer. Studies have shown that while most prostate cancer sufferers have raised PSA level, this test is somehow not specific. This means that the false positive rate is quite high. Even though one has high level of PSA, he may not have prostate cancer.

There are a few recognized causes for raised PSA, all of them are associated with irritation of the prostate:

1. Benign Prostatic Hyperplasia – enlarged prostate due to aging
2. Prostatitis – inflammation of prostate (can be infection or non-infection)
3. Prostate cancer
4. Recent ejaculation (avoid testing PSA in 48 hours)
5. Recent prostate biopsy (avoid testing PSA in 6 weeks)
6. Recent prostate surgery
7. Recent digital rectal examination (avoid testing PSA in 1 week)
8. Recent urinary cathetherization
9. Urinary retention
10. Recent rigorous exercise esp bicycle riding

 

   Benign Prostatic Hyperplasia

Generally the cut off point for PSA value is set at 4.0ng/ml. Since PSA level is age-dependent as prostate gland will increased in size with age, some authorities suggest to modify it according to age.

Age	“Normal” PSA (ng/ml)
40-49	<2.5
50-59	<3.5
60-69	<4.5
70-79	<6.5

Although PSA <4.0ng/ml is widely considered as normal, there is still a possibility of prostate cancer (about 20% chance) in these people. PSA between 4.0 and 10.0ng/ml is considered borderline (25% chance of prostate cancer), while PSA >10.0ng/ml has higher risk (67% chance of prostate cancer).

Since the false positive rate is quite high, PSA may not be a good cancer marker as it can cause unnecessary further investigation and anxiety. Digital rectal examination (a finger is inserted into rectum) is usually done to feel for abnormality in the gland. For men with higher risk of prostate cancer such as old age and positive family history, further test such as prostate ultrasound and biopsy may be needed. For those with low risk, other causes of raised PSA should be looked for and treated accordingly. The PSA level can be repeated after 6-12 weeks to see the trend. If it continues to rise significantly, then further investigation is warranted. Another blood test that can be done is free/bound PSA ratio. More free PSA compared to bound PSA is good news. The standard PSA test is total PSA (free + bound).

Whether you should have your PSA checked depends on you. One one hand it may save your life by detecting prostate cancer early, on the other hand it may cause unnecessary anxiety, loss of money and complication from further investigation.