Prostate-Specific Antigen (PSA)

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

Using the PSA test to screen healthy men for prostate cancer is not recommended at present in the UK. Currently there is no evidence to show that the overall benefits of a PSA- based screening programme outweighs the risks. PSA is still a poor test for prostate cancer detection (low specificity) and it has led to harm of over-diagnosis and over-treatment in up to 50 % of men. A PSA test does not distinguish a slow-growing cancer from a fast-growing cancer.

Risk factors for prostate cancer include;

• Increasing age
• Black ethnicity
• Family history of prostate cancer
• Being overweight or obese (especially in advanced prostate cancer)

Your healthcare professional will take these risk factors into account to give you the best available information and support your decision.

The Public Health England website has a guidance document on Prostate Cancer Risk Management Programme (PCRMP). It includes a summary sheet on advice for well men aged 50 and over.

Two other PSA tests are also available and may be requested; ratio of free to total PSA (f/t PSA) or complex PSA (cPSA). These tests may improve the specificity and reduce the number of unnecessary biopsies. It is helpful when patient’s total PSA value < 10 µg/L (which is known as the diagnostic “grey zone”) with negative DRE It may distinguish between prostate cancer and other non-cancerous conditions such as benign prostatic hypertrophy (BPH). Studies suggest that using these PSA isoforms in men who fall into this grey zone could potentially reduce over diagnosis and maintain a high cancer detection rate.

The 'normal' value for total PSA varies with age and is generally considered to be less than 3.0 micrograms (µg) per litre (L) in men aged 50-69 years. Recent literature shows that age-specific PSA cut-offs for detecting prostate cancer is highly variable. It may differ with patient’s demographics and clinical characteristics.

A high serum PSA result >3 µg/L alone does not automatically lead to other investigations e.g; prostate biopsy. There are several other factors to be considered; such as prostate size, digital rectal examination (DRE) findings, age, ethnicity, family history of prostate cancer, body weight, co-morbidities, history of any previous negative biopsy or any previous PSA history. Your healthcare professional may consider these factors along with raised PSA (> 3 ng/mL) result when referring patients to specialist care.

Total PSA level greater than 10.0 µg/L may indicate a high probability of prostate cancer. Results between 2.0 µg/L and 10.0 µg/L may be due to BPH, a non-cancerous swelling of the prostate that occurs most frequently in older 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 percentage 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 2.0 to 10.0 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. 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 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. Reference ranges can be 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. A blood test for PSA measurement must be performed 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. 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. Some chemotherapeutic drugs, such as cyclophosphamide, methotrexate, and also other medications such as aspirin, statins, diuretics, finasteride, and dutasteride may affect PSA results.

The most common treatments are discussed elsewhere on this site. For more information visit the Macmillan cancer support website.