Prostate-specific antigen (PSA)

PSA is measured to help detect prostate cancer, and also to monitor the response to treatment in those with prostate cancer. However many elevations of PSA are not due to prostate cancer.

Using the PSA test to screen healthy men for prostate cancer is somewhat controversial and the National Health and Medical Research Council and the Royal College of General Practitioners of Australia do not recommend PSA as a screening test in men who have no symptoms and no family history of prostate cancer. This is because in many cases PSA testing detects early cancers that are extremely slow-growing and may never cause life-threatening disease - this may cause further unnecessary testing and treatment. Guidance on this issue can be found on the Prostate Cancer Foundation website and by looking at this visual decision aid. However, men who have an increased risk for prostate cancer (such as Afro-Caribbean or African-American men, and those with a family history of the disease) may wish to be screened for prostate cancer.

The total PSA test and DRE may also be ordered when a man has symptoms that could be due to prostate cancer, such as difficult, painful, and/or frequent urination, back pain, and/or pelvic pain. Since these symptoms are seen with a variety of other conditions, including infection and prostatitis, the doctor will also frequently order other tests, such as a urine culture. Some of these conditions can themselves cause temporary increases in PSA levels. If a total PSA level is elevated, a doctor may order a repeat test a few weeks later to determine whether the PSA concentrations have returned to normal.

Free PSA is sometimes requested when total PSA levels are only mildly elevated to try to differentiate between prostate cancer and other non-cancerous conditions such as BPH. It might also be requested in combination with other tests, such as the rectal examination or biopsy, to help confirm a diagnosis of prostate cancer. Once the diagnosis is made, the PSA test might also be used to help your doctor learn about how you are responding to treatment.

The 'normal' value for total PSA are age dependent but total PSA levels greater than 10.0 µg/L may indicate a high probability of prostate cancer. Levels below 10.0 µg/L but above the usual level found in elderly men may indicate BPH, a non-cancerous swelling of the prostate, or prostate cancer. BPH occurs most frequently in elderly men. Increased total PSA levels may also indicate a condition called prostatitis, which is caused by an infection. It is important to realise that an elevated PSA level does not always indicate the presence of prostate cancer.

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 µg/L. This test may also be useful in early diagnosis of disease when values are between 2.5 and 4.0 µg/L. 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 associated with a more aggressive form of the disease. Additional studies are ongoing.

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 is for a particular test. 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 be influenced by the test method and instrument used by laboratory. To learn more about reference ranges click on the green panel below.

About Reference Intervals

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. It is also thought that a rectal examination prior to PSA testing might temporarily raise PSA levels but recent studies have not shown this to be a consistent finding. Excessive doses of some chemotherapeutic drugs, such as cyclophosphamide and methotrexate, may also increase or decrease PSA levels.

The most common treatments are discussed elsewhere on this site. For more information visit the sites listed in the Related information section.

The incidence for disease is greater among Afro-Caribbeans and African-Americans than for Caucasian men. Hence men from these ethnic groups may wish to have their PSA tested earlier than usual.

No. Sometimes cancer cells do not produce much PSA, and the test will be negative when the disease is present.

PSA Density refers to the relationship of the PSA level to the size of the prostate measured by ultrasound examination.

PSA Velocity refers to how quickly PSA levels change over time.

PSA Doubling Time is the time it takes for the PSA value to double. This may be useful in following treatment and determining the type of treatment.