The prostate-specific antigen (PSA) test is used primarily to screen for prostate cancer. PSA is a protein produced by both cancerous and noncancerous tissue in the prostate, a small gland in men that produces some of the fluid in semen. When cancer develops in the prostate, the cells begin to multiply uncontrollably. This causes PSA levels to rise. PSA screening may help detect prostate cancer early, before symptoms develop, while treatment may still be most effective.
PSA Testing
Most major medical organizations recommend PSA screening starting at age 50 for men at average risk of prostate cancer and at age 45 for men at high risk, such as those with a first-degree relative diagnosed with prostate cancer before age 65. These age recommendations are guidelines, and screening should still be considered based on a man’s preferences, health and family history.
A healthcare provider will draw a blood sample and check it for PSA levels. There is no specific normal or abnormal PSA level – in general PSA levels under 4 nanograms per milliliter (ng/mL) are considered normal, while levels over 10 ng/mL are considered high. If PSA levels are elevated, additional testing, such as a digital rectal exam or prostate biopsy, may be recommended to check for cancer.
Interpreting PSA Results
There are several factors that can affect PSA levels besides cancer. Levels normally increase slowly as men age. Inflammation or infection of the prostate can also cause temporary rises in PSA. Certain factors may artificially lower PSA as well, such as taking certain medications like finasteride or herbal supplements like saw palmetto.
PSA levels between 4-10 ng/mL are considered borderline and should be monitored with repeat testing. Rises in PSA over time, even if still within the normal range, can indicate higher cancer risk. The rate PSA rises, known as PSA velocity, is sometimes used along with the absolute level to assess prostate cancer risk.
| PSA Level | Interpretation |
|---|---|
| 0 to 2 ng/mL | Very low |
| 2 to 3 ng/mL | Slightly elevated |
| 4 to 10 ng/mL | Borderline – Repeat testing recommended |
| Greater than 10 ng/mL | Highly elevated – Further testing warranted |
Benefits of PSA Screening
There are several potential benefits of PSA screening when used appropriately:
- Early detection – PSA testing can detect prostate cancer before symptoms occur, which may allow for more effective treatment.
- Peace of mind – Normal PSA levels can provide reassurance that cancer is unlikely.
- Improved survival – Some studies have found that PSA screening improves 5-year survival rates for prostate cancer when combined with appropriate follow-up testing and treatment.
The introduction of PSA screening in the late 1980s contributed to an increase in early prostate cancer detection. However, there is debate about whether this has translated to reduced deaths from the disease.
Limitations of PSA Screening
While widely used, PSA screening also has important limitations, including:
- Overdiagnosis – Elevated PSA may detect small prostate tumors that would never have caused harm or required treatment during a man’s lifetime. This can lead to unnecessary procedures and anxiety.
- False positives – Other factors besides cancer can raise PSA, which may prompt biopsy or other tests that show no cancer.
- Unnecessary treatment – Detecting low-risk cancers early may prompt aggressive treatment that causes side effects, with little benefit.
- False negatives – PSA levels may stay within the normal range even when cancer is present, particularly with aggressive disease.
Different medical organizations have differing stances on PSA screening based on their assessment of these benefits and risks. While some still recommend it, others caution more selective screening for older men or those at high risk.
PSA and Prostate Biopsy
If PSA levels are elevated or rising rapidly based on age-specific norms, a prostate biopsy is often the next step to determine if cancer is present. During a biopsy, small tissue samples are taken from different areas of the prostate for examination under a microscope.
PSA levels can provide guidance on how extensive the biopsy needs to be. In general:
- PSA under 10 ng/mL – Standard biopsy with 10-12 tissue samples
- PSA 10-20 ng/mL – Extended biopsy with 20+ samples
- PSA above 20 ng/mL – Saturation biopsy with 30+ samples
Higher PSA levels indicate a greater chance of high-grade cancer being present. Taking more biopsy samples can help ensure no cancer is missed. However, more samples also increase the risk of bleeding and infection from the biopsy procedure itself.
PSA Screening in High Risk Groups
Certain categories of men are at increased risk of prostate cancer and may benefit from earlier or more frequent PSA screening:
- Family history – Men with a first-degree relative (father, brother, son) diagnosed with prostate cancer, especially before age 65.
- African American men – Incidence and mortality rates for prostate cancer are higher in African American men compared to the general population.
- BRCA mutations – Men who inherit BRCA1 or BRCA2 genetic mutations have higher prostate cancer risk.
- Veterans – Some studies show higher prostate cancer rates in veterans exposed to Agent Orange or who served at Camp Lejeune.
Current guidelines recommend possibly beginning screening at age 45 for high-risk groups instead of the age 50 benchmark for average-risk men. More frequent PSA testing, such as yearly instead of every other year, may also be appropriate.
PSA Trends After Prostate Cancer Treatment
PSA levels are monitored periodically after treatment for prostate cancer to check for potential recurrence. Different expectations apply compared to screening normal men:
- After prostatectomy (surgical removal of the prostate), PSA should become undetectable.
- After radiation therapy, PSA may not decline as far but should reach a low nadir value.
- Slowly rising PSA after treatment often indicates recurrent cancer before clinical symptoms appear.
PSA screening after prostate cancer treatment is considered part of appropriate follow-up care. How often to test PSA depends on individual factors like cancer aggressiveness and life expectancy.
Other Prostate Cancer Screening Tests
While PSA is the most widely used prostate cancer screening test, other options include:
- Digital rectal exam (DRE) – A doctor feels the surface of the prostate through the rectum to check for abnormalities.
- Prostate MRI – Multiparametric prostate MRI provides images of the prostate that may detect high-grade cancer. Often used to guide prostate biopsy if PSA is elevated.
- PCA3 test – Measures levels of PCA3, a gene overexpressed in prostate cancer cells, in urine after a digital rectal exam.
- 4Kscore – Blood test that combines PSA level with three other prostate cancer markers.
These additional tests may be helpful for screening or in men with persistently elevated PSA but prior negative biopsies. However, PSA remains the first-line prostate cancer screening test for most men.
Conclusion
The PSA test allows early detection of prostate cancer, which may improve outcomes. However, PSA screening remains controversial given concerns about overdiagnosis and overtreatment of less aggressive disease. Before undergoing PSA testing, men should understand the potential benefits, limitations and uncertainties of screening. An informed, shared decision-making approach with their healthcare provider is recommended to determine if PSA screening is appropriate based on individual risk factors and preferences.