What do PSA tests tell?
The epithelium of the prostate gland secretes a protein known as prostate-specific antigen, PSA, which is a serine protease consisting of 23 amino acids. PSA is an enzyme that keeps semen in liquid form.
PSA is specific to the prostate and is not secreted by other tissues. Because PSA is secreted by both cancer cells and healthy glandular cells in the prostate, cancer diagnosis based on PSA is challenging.
When evaluating the significance of a PSA reading, the size of the prostate should always be taken into account. The larger the prostate, the higher the PSA level. A prostate of 30–40 ml in size results in elevated PSA levels of 3–4 mcg/l.
Prostate cancer may be present even if the man’s PSA levels are very low. The following can be used as a general guide to total reference PSA values in different age groups:
PSA is present in blood both free and bound to proteins, mainly to alpha-chymotrypsin and macroglobulins. The levels of free PSA are important when trying to distinguish between benign and malignant changes. The lower the free PSA level, the higher the cancer risk.
Prostate cancer risk can be evaluated on the basis of the free-to-total PSA ratio, i.e. the percentage of free PSA out of total PSA, as follows:
(Sources: Thompson et al.: Prevalence of prostate cancer among men with a prostate-specific antigen level < or = 4.0 ng per milliliter, New England Journal of Medicine, 2004, May 27, and Finnish Current Care guidelines).
It is important to note that PSA levels increase more than tenfold during an infection, particularly during a urinary tract infection. Accurate PSA readings can only be obtained two to three months after an infection. Mild prostatitis or intercourse on the previous night may also increase PSA levels. On the other hand, it appears a digital rectal examination does not increase the PSA value.
Taking a repeat PSA test is always a good idea. A single elevated PSA reading does not always require a biopsy. If, however, a clearly elevated PSA level is found on a single occasion and remains unexplained, i.e. the patient has no symptoms of prostatitis or urinary tract infection, a biopsy should be taken without delay.
The more often PSA levels are measured, the easier it is to evaluate the likelihood of a malignant lesion. It is therefore recommended that the rate at which PSA levels rise should be used in assessing the risk of malignancy instead of fixed PSA reference levels. The risk can be assessed using either PSA velocity (the rate at which the PSA level rises) or the PSA doubling time (the time it takes for a man’s PSA level to double).
An annual increase of 0.5–0.7 mcg/l is an acceptable rate. A PSA doubling time of less than a year indicates an active process in the prostate, whereas a PSA doubling time of three years suggests the situation is calm. An increase of 2 mcg/l has been found to indicate an aggressive prostate cancer that should be treated – even if the total PSA level is low.
Measuring the PSA velocity and the PSA doubling time is particularly recommended to monitor the patient for prostate cancer recurrence after radical surgery or radiotherapy. Prostate cancer diagnostics and treatment should particularly target men with aggressive prostate cancer that may have a significant impact on their lifespan.
Based on screening studies and Finnish Cancer Registry data on prostate cancer incidence, an annual PSA test is recommended for men aged over 50. The tests can be arranged by the man’s occupational health care provider, at a local health centre or privately. PSA testing should start at an earlier age if the man’s father or another close relative has been diagnosed with prostate cancer.
PSA is specific to the prostate and is not secreted by other tissues. Because PSA is secreted by both cancer cells and healthy glandular cells in the prostate, cancer diagnosis based on PSA is challenging.
When evaluating the significance of a PSA reading, the size of the prostate should always be taken into account. The larger the prostate, the higher the PSA level. A prostate of 30–40 ml in size results in elevated PSA levels of 3–4 mcg/l.
Prostate cancer may be present even if the man’s PSA levels are very low. The following can be used as a general guide to total reference PSA values in different age groups:
| Age (yrs) | S-PSA ( µg/l ) |
| 40-49 | less than 2,5 |
| 50-59 | less than 3,5 |
| 60-69 | less than 4,5 |
| 70-79 | less than 6,5 |
PSA is present in blood both free and bound to proteins, mainly to alpha-chymotrypsin and macroglobulins. The levels of free PSA are important when trying to distinguish between benign and malignant changes. The lower the free PSA level, the higher the cancer risk.
Prostate cancer risk can be evaluated on the basis of the free-to-total PSA ratio, i.e. the percentage of free PSA out of total PSA, as follows:
| Total PSA (µg/l) | Cancer risk (%) |
| 0-2 | 10 % |
| 2-4 | 15 % |
| 4-10 | 30 % |
| over 10 | over 50 % |
| Free PSA amount (%) | Cancer risk (%) |
| 0-10 | 56 % |
| 10-15 | 28 % |
| 15-20 | 20 % |
| 20-25 | 16 % |
| over 25 | 8 % |
(Sources: Thompson et al.: Prevalence of prostate cancer among men with a prostate-specific antigen level < or = 4.0 ng per milliliter, New England Journal of Medicine, 2004, May 27, and Finnish Current Care guidelines).
It is important to note that PSA levels increase more than tenfold during an infection, particularly during a urinary tract infection. Accurate PSA readings can only be obtained two to three months after an infection. Mild prostatitis or intercourse on the previous night may also increase PSA levels. On the other hand, it appears a digital rectal examination does not increase the PSA value.
Taking a repeat PSA test is always a good idea. A single elevated PSA reading does not always require a biopsy. If, however, a clearly elevated PSA level is found on a single occasion and remains unexplained, i.e. the patient has no symptoms of prostatitis or urinary tract infection, a biopsy should be taken without delay.
The more often PSA levels are measured, the easier it is to evaluate the likelihood of a malignant lesion. It is therefore recommended that the rate at which PSA levels rise should be used in assessing the risk of malignancy instead of fixed PSA reference levels. The risk can be assessed using either PSA velocity (the rate at which the PSA level rises) or the PSA doubling time (the time it takes for a man’s PSA level to double).
An annual increase of 0.5–0.7 mcg/l is an acceptable rate. A PSA doubling time of less than a year indicates an active process in the prostate, whereas a PSA doubling time of three years suggests the situation is calm. An increase of 2 mcg/l has been found to indicate an aggressive prostate cancer that should be treated – even if the total PSA level is low.
Measuring the PSA velocity and the PSA doubling time is particularly recommended to monitor the patient for prostate cancer recurrence after radical surgery or radiotherapy. Prostate cancer diagnostics and treatment should particularly target men with aggressive prostate cancer that may have a significant impact on their lifespan.
Based on screening studies and Finnish Cancer Registry data on prostate cancer incidence, an annual PSA test is recommended for men aged over 50. The tests can be arranged by the man’s occupational health care provider, at a local health centre or privately. PSA testing should start at an earlier age if the man’s father or another close relative has been diagnosed with prostate cancer.