اختبار PSA

Cross-section diagram of the prostate and nearby organs

What is a PSA test?

The PSA test (prostate specific antigen) is a blood test that measures the level of prostate specific antigen in the blood. PSA is a protein which is made by the prostate gland. The PSA level in the bloodstream is measured in nanograms per millilitre (ng/mL). PSA is made by normal prostate cells but also by prostate cancer cells.

Before having a PSA test, it is important not to have:

• An active urine infection.

• Produced semen during sex or masturbation (ejaculated) in the previous 48 hours.

• Exercised heavily in the previous 48 hours.

• Had a prostate biopsy in the previous six weeks.

• Had an examination of the back passage with a gloved finger (a digital rectal examination) in the previous week.

• Had receptive anal intercourse for a period of 48 hours before a PSA test.

Each of these may produce an unnaturally high PSA result, resulting in unnecessary further investigations.

In England, the PSA test may be offered to any man aged 50 and over who requests it as long as they have considered the pros and cons of having the test. The test may be offered to younger men who have a higher risk of prostate cancer.

The normal range changes as men age.

There are no age-specific reference limits for men older than 80 years of age. Any referral will depend on local guidelines.

Generally, the higher the level of PSA, the more likely it is to be a sign of cancer.

Benefits of PSA testing

• PSA testing may lead to prostate cancer being detected earlier, before symptoms develop.

• Detecting prostate cancer early before symptoms develop may improve the outcome (prognosis) and improve the chance of a complete cure.

Limitations and risks of PSA testing

• False negative result: about 15 out of 100 men with a negative PSA test may have prostate cancer.

• False positive result: about 75 out of 100 men with a positive PSA test have normal prostate investigations, ie no evidence of cancer.

• A false positive PSA test may lead to unnecessary investigations, such as a prostate biopsy, and there may be side-effects from this investigation, such as bleeding or infection. This is less common nowadays as MRI scans are a more common initial investigation which carry lower risks.

• A positive result may also lead to unnecessary treatment. Many prostate cancers are slow growing and may not become evident during a man's lifetime. Side-effects of treatment are common and can be serious, such as urinary incontinence and sexual problems.

• Current statistics suggest that, in men between the ages of 50 and 66 who are screened for 13 years, annual PSA testing would result in the avoidance of death from prostate cancer of 1.3 per 1000 men.

A raised PSA level may be due to a diagnosis prostate cancer but about three out of four men with a raised PSA level will not be found to have prostate cancer.

Other conditions may also cause a raised PSA level, including:

• Inability to pass urine, causing an enlarged bladder (acute retention of urine).

• Enlargement of the prostate that is non-cancerous (benign).

• Older age.

• Urine infection.

• التهاب البروستاتا الحاد.

• Transurethral resection of the prostate (TURP) operation. TURP is a prostate operation used if you have benign enlargement of the prostate.

• Having a catheter in place to help pass urine.

If the PSA level is not raised

Prostate cancer is less likely. A digital rectal examination may also be needed to rule this out.

If the PSA level is slightly raised

Prostate cancer is less likely. A digital rectal examination may also be needed to rule this out. Annual PSA tests might be advised.

If the PSA level is definitely raised

The GP will do an urgent referral to a urologist (a specialist doctor) for further tests for prostate cancer. The specialist will discuss the options for further investigations, which may include a sample taken (خزعة) of the prostate gland and an فحص الرنين المغناطيسي.

For information about the treatment options for prostate cancer, see the separate leaflet called Prostate cancer.