PSA

PSA is measured to help detect prostate cancer, and also to monitor the response to treatment in those with prostate cancer.

Using the PSA test to screen healthy men for prostate cancer is somewhat controversial and is not recommended at present in the UK. This is because, in many cases, PSA testing detects early cancers that are extremely slow-growing and may never cause life-threatening disease. PSA testing may therefore cause further unnecessary testing and treatment. Men who have an increased risk for prostate cancer (such as Afro-Carribean or African-American men, and those with a family history of the disease) may wish to be screened for prostate cancer. The NHS and CancerBACUP have produced a booklet called ‘Understanding The PSA Test’ for men who require further information about the PSA test and prostate cancer. There is also an online decision aid called PROSDEX that describes the facts clearly and will help you understand the advantages and disadvantages of having your PSA measured.

Two other PSA tests are also available and may be requested; free PSA or complexed PSA. These tests are not widely used in the UK; they provide similar information, and their clinical value remains unclear. Free PSA is sometimes requested when total PSA levels are only mildly elevated to try to distinguish between prostate cancer and other non-cancerous conditions such as benign prostatic hypertrophy (BPH). Free PSA might also be requested in combination with other tests, such as the rectal examination or biopsy, to confirm a diagnosis of prostate cancer. Once the diagnosis is made, the PSA test can also be used to help your doctor learn about how you are responding to treatment.

The 'normal' value for total PSA varies with age and is generally considered to be under 3.0 nanograms (ng) per millilitre (mL) in men under 60 years of age of blood, under 4.0 ng per mL in men 60 - 69 years of age, and under 5.0 ng per mL in men over 70 years of age. Total PSA levels greater than 10.0 ng/mL may indicate a high probability of prostate cancer. Increased levels of PSA in those with a small prostate gland volume (which can be measured using ultrasound at the time of biopsy) indicate a higher probability of cancer. Levels between 4.0 ng/mL and 10.0 ng/mL may be due to BPH, a non-cancerous swelling of the prostate which occurs most frequently in elderly men. Increased total PSA levels may also indicate a condition called prostatitis, which is caused by an infection.

There is some evidence that the free PSA ratio (the percent of total PSA not bound to proteins) can help predict the probability of cancer, especially in patients with total PSA levels in the 'grey-area’ range of 4.0 to 10.0 ng/mL. This test may also be useful in early diagnosis of disease when values are between 2.5 and 4.0. A free-PSA test result above 25% is thought to suggest a lower risk of cancer, whereas a lower percentage suggests a higher probability of disease. This ratio may help reduce the number of unnecessary biopsies. A recent study also suggests that very low ratios of free PSA to total PSA (less than 14%) might be seen with a more aggressive form of the disease. Further studies are now being undertaken.

In most cases, test results are reported as numbers rather than as "high" or "low", "positive" or "negative", or "normal". In order for the doctor to properly understand laboratory results it is necessary for them to know what the reference range (or ‘normal value’ range) is for the laboratory where the test is performed. However, reference ranges can be influenced by the patient's age and sex and, amongst other things, by what drugs they are receiving, the time of day and what they have eaten. Reference ranges can also influenced by the test method and instrument used by laboratory. To learn more about reference ranges, please read the article, Reference Ranges and What They Mean.

Prostate biopsy or operations on the prostate will significantly elevate PSA levels. The blood test should be done before surgery or six weeks after.

Ejaculation and vigorous physical activity affecting the prostate, such as bicycle riding, may cause a temporary rise in PSA levels. A blood sample should be taken either before a digital rectal examination as pressure on the gland during the examination will lead to an increase in the PSA value or alternatively after at least a week after the examination Excessive doses of some chemotherapeutic drugs, such as cyclophosphamide and methotrexate, may increase or decrease PSA levels.