Prostate-specific antigen (PSA)
PSA is short for prostate-specific antigen. PSA (S-PSA) is a protein whose function is to prevent the coagulation of semen and to liquefy it. PSA is secreted by the cells of the prostate gland. PSA is only produced in the prostate gland, from which small amounts of it enter the bloodstream. PSA is not produced by other tissues, so all PSA is always from the prostate gland.
Normally, small amounts of PSA are released into the blood. With age, the prostate gland normally grows, increasing the amount of PSA in the bloodstream. The bigger the prostate gland, the more PSA protein is therefore released into the blood. More PSA also leaks into the blood in the case of prostate cancer.
Some of the PSA in the bloodstream is free and some is bound to other proteins. The half-life of PSA in the blood is 2–4 days if its level is temporarily elevated.
When should PSA be measured?
PSA is usually tested when investigating prostate enlargement or suspecting prostate cancer. It is also used in the follow-up to diagnosed prostate cancer and its possible treatment.
Checking PSA levels is a good idea in connection with the following symptoms:
- Urinating takes a long time
- The need to urinate becomes more frequent
- Weak stream
- Suspicion of prostate cancer
What does the PSA test measure?
The PSA test indicates the level of PSA in the blood. However, it does not indicate whether the elevated level is caused by benign prostate enlargement or the possibility of prostate cancer. Moreover, a normal PSA level does not exclude prostate cancer. The test determines the total concentration of PSA.
How to interpret the PSA test result?
The size of the prostate gland increases with age. Therefore, reference values are specified separately for different age groups. Normally, the result is:
Reference value, PSA:
- Under 56 y: < 3,3 ug/l
- 56 – 59 y: < 3,8 ug/l
- 60 – 63 y: < 4,8 ug/l
- 64 - 67 y: < 5,8 ug/l
- under 67 y: 6,2 ug/l
If the level is below 2 µg/l or higher than 20 µg/l, the ratio of free PSA to total PSA (S–PSA-V/T) is not determined. In these cases, the PSA result is not significant to the health. If the resultis between 2 and 20, also free PSA is measured. The reference value of relation between total and free PSA is >15 %.
Many different factors can influence the fluctuation in PSA levels from one day to another. Before sampling, causes that increase the PSA level should be taken into consideration:
- Ejaculation less than 48 hours before sampling
- Urinary retention, meaning that the bladder fills up with urine, but it cannot be voided
- Urinary tract infection
- Prostate massage
- Prostate biopsies
- Long bicycle ride
The reference values of this examination have changed 11.10.2021. You will find your own result's reference values from My LOUNA in touch with the graph.
Please contact your physician or other healthcare professional if you suspect an illness or need help interpreting the results.
What can cause elevated levels in the PSA?
The PSA level in the blood increases in the following conditions.
- Prostate cancer
- Benign prostate enlargement
- Urinary tract infections
When the PSA level in the blood is 4–10 µg/l, the probability of prostate cancer is approximately 25 per cent. When the level exceeds 10 µg/l, the probability of prostate cancer is over 50 per cent. A low PSA level does not guarantee that there is no cancer, because sometimes the cancer cells release small amounts of PSA into the blood. Sometimes prostate cancer can grow so slowly that it will not cause any problems even if untreated.
What can cause decreased levels in the PSA?
PSA is normally low (below the reference values).
The most typical additional PSA tests:
- Testosterone (2735 S-Testo)
- SHBG (2737 S-SHBG)
- Creatinine (2143 S -Krea)
SYNLAB test list: Prostate-specific antigen (3642 S-PSA) https://www.yml.fi/tuotekuvaus_show.php?tuotenro=306
SYNLAB tests: PSA https://www.yml.fi/tuotekuvaus_show.php?tuotenro=306
Terveyskirjasto health library: Prostataspesifinen antigeeni, ”eturauhaskoe” (P-PSA) https://www.terveyskirjasto.fi/terveyskirjasto/tk.koti?p_artikkeli=snk03230&p_hakusana=psa
ERSY Eturauhassyöpäpotilaiden tuki ry: PSA http://ersy.fi/psa.php
Lab Test Online: Prostate-Specific Antigen (PSA) https://labtestsonline.org.uk/tests/prostate-specific-antigen-psa
Fasting is not required
This examination does not require fasting