The main prostate cancer screening test for men who show no symptoms of the disease is the prostate specific antigen (PSA) blood test. This screening test measures the amount of PSA in the blood, a protein which is found at elevated levels in men who have prostate cancer. However, the PSA blood test is not always a reliable indicator that a man has prostate cancer.
What Can Cause Elevated Prostate Specific Antigen (PSA) Levels Besides Prostate Cancer?
The PSA blood test can result in a large number of false positives, with over 60% of men who show elevated PSA levels not actually having prostate cancer. There are several factors other than prostate cancer that can elevate PSA levels in men. These include:
- the presence of Benign Prostate Hyperplasia (BPH), which is when a man has an enlarged prostate, a condition that is non-cancerous
- a prostate infection, also known a prostatitis
- age, since as men get older PSA levels generally rise
- ejaculation, which can cause a short-time rise in PSA levels
What Factors Can Reduce the PSA Level in the Blood?
Several factors are now known to reduce the PSA level in the blood, even when prostate cancer is present. Therefore, in a very small number of cases some men who have prostate cancer do not show elevated PSA levels. Factors that can reduce PSA in the blood include:
- some drugs that are used in the treatment of BPH e.g., finasteride and dutasteride
- some herbal supplements that are marketed for improved prostate health, e.g., saw palmetto
- obesity, as men with increased body fat tend to show lower PSA levels
What is the Cut-off level used for the PSA Blood Test?
Many doctors use a cut-off PSA level of 4ng/mL blood as an indication for follow up when carrying out prostate cancer screening. However, other ways of interpreting the PSA blood test to suggest prostate cancer are sometimes used because of the unreliability of this test. For example, some doctors use age-specific PSA level cut-offs while others look at the change in PSA level over time.
The PSA blood test is the main prostate cancer screening test, and is often done in combination with a DRE (Digital Rectal Examination), where the doctor inserts a gloved finger up the man’s rectum in order to feel for any abnormalities on the prostate gland. While the PSA blood test is not fool-proof, it is a screening test. Therefore it can give an indication in many cases of whether a man may have prostate cancer when elevated PSA levels are seen; however, actual diagnosis of prostate cancer can only be done by following up with a prostate biopsy to analyse the cells of the prostate for cancer markers.
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Sources:
American Cancer Society, ‘Prostate Cancer; Early Detection’, Updated March 2010, Accessed 20 May 2010
Andrology Australia 2006, ‘PSA Test’, Updated February 2006, Accessed 20 May 2010
National Cancer Institute 2009, ‘Prostate-Specific Antigen (PSA) Test’, Updated March 2009, Accessed 20 May 2010
Christine Redmond - My interest in science and healthcare has seen me working in the laboratory with tiny cells and DNA to helping set up a cancer clinical ...
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