PSA Screening Test: Purpose, Results, Benefits, and Risks

Though most cases of prostate cancer have a good prognosis, the disease is the second leading cause of cancer deaths in American men, according to the American Cancer Society.

As with other cancers, it’s best to catch prostate cancer at an early stage when treatment may be more effective and elicit fewer, less severe side effects. The most common screening test for prostate cancer is the prostate-specific antigen or PSA blood test, which measures the levels of the PSA enzyme in the blood.

The prostate is a walnut-sized gland, situated between the bladder and penis, that's part of the male reproductive system. Its main function is to produce fluid that partly makes up semen, which helps transport and protect sperm produced by the testicles.

The prostatic fluid contains various substances that help sperm cells function and survive. One of these substances is PSA.

PSA thins or loosens up semen, allowing sperm cells to swim freely while in the female body.

Some of the PSA produced by prostate cells also makes its way into the blood.

A person’s PSA levels increase with age — likely an evolutionary adaptation that allowed those with this trait to sire more offspring than other males.

The PSA screening blood test measures the levels of PSA circulating in the blood.

Both normal prostate cells and cancer cells make PSA. While prostate cancer cells tend to produce less PSA than normal cells, they allow PSA to more easily pass through the cell wall and eventually wind up in the bloodstream.

This suggests that elevated PSA levels in the blood could signify prostate cancer.

The U.S. Food and Drug Administration (FDA) initially approved the PSA blood test to monitor the progression of prostate cancer. In 1994, the FDA approved the test to be used as a screening tool to aid in the detection of prostate cancer in men 50 years or older.

Most healthy men have PSA levels in the blood less than 4 nanograms per milliliter (ng/mL). The chance of having prostate cancer goes up as PSA concentrations increase.

But some people with low PSA levels (below 4 ng/mL) have gotten prostate cancer while others with high PSA levels (between 4 ng/mL and 10 ng/mL) have not. This is partly because various factors can affect PSA production and test results.

Long-term factors that can increase PSA levels include:

• Prostatitis, or prostate inflammation
• Enlarged prostate
• Older age
• Urinary infection

Recent ejaculation and prostate stimulation — including from anal sex, per research, and even a long bike ride, according to the Prostate Cancer Foundation — can also temporarily cause high PSA levels.

Additionally, obesity and certain medications — finasteride (Propecia) and dutasteride (Avodart), which are used to treat enlarged prostate — can lower PSA levels.

Given the uncertainties with PSA test results, only a prostate biopsy (removal of prostate tissue through an invasive procedure for analysis) can diagnose prostate cancer.

RELATED: What a High PSA Level Means if It’s Not Prostate Cancer

The PSA blood test was used for annual prostate cancer screenings until about 2008, when scientists learned more about its benefits and harms. A controversy bloomed as experts tried to determine if the benefits of annual prostate cancer screenings outweigh the risks.

A main issue identified is that the PSA blood test cannot differentiate between benign (noncancerous) and malignant (cancerous) tissue. A high PSA test result could unnecessarily cause considerable anxiety if a man doesn’t have prostate cancer.

In addition, some men may choose to skip the biopsy that confirms the diagnosis and go directly to starting treatments, which can have side effects such as impotence, incontinence, and bowel issues.

In 2012, the U.S. Preventive Services Task Force (USPSTF), an independent panel of experts that makes evidence-based recommendations about clinical preventive services, found little benefit and significant harm to routine PSA blood tests to screen for prostate cancer. It subsequently recommended against these tests.

The USPTF updated its recommendation in 2018 to reflect new evidence of the benefits of PSA screenings on prostate cancer death rates. For men 55 to 69 years old, it recommends making a joint decision with a doctor whether to undergo periodic PSA screening after discussing the risks and benefits of screening.

The USPSTF recommends against prostate cancer screening for men over 70.

Many other professional healthcare organizations, associations, and societies have similar recommendations for prostate cancer screening. Screening is also recommended for:

• Younger men with a family history of prostate cancer or related cancers
• Men who carry a BRCA1 or BRCA2 mutation
• African American men, who are more likely to develop aggressive prostate cancer, beginning around age 45

Screening could also be considered for men 70 years and older who are expected to live for at least another 10 years.

Recent data from the National Cancer Institute shows that prostate cancer mortality rates in the United States from 1992 to 2017 declined by nearly 50 percent, largely due to PSA screening.

If a PSA screening blood test shows slightly elevated PSA values, your doctor may recommend another PSA test a couple weeks later. If you have two abnormal PSA values and a reasonable life expectancy of at least 10 years, your doctor may recommend a prostate biopsy to confirm you have prostate cancer.

Your doctor may also recommend a biopsy if you have:

• A family history of prostate cancer, multiple cancers, or Lynch syndrome
• African descent
• A quick rise in PSA levels over a year
• Abnormal lumps found during a digital rectal exam

Prostate cancer grows slowly, so some men who have it may never need treatment. Rather than unnecessarily treating a slow-growing cancer, your doctor may recommend active surveillance if you have low-risk cancer.

Research shows that men who undergo treatment do not appear to live longer than those who undergo active surveillance, according to the American Cancer Society.

During active surveillance, PSA is used as a biomarker, meaning that PSA levels are measured periodically to keep track of the severity and progression of the cancer. You may need to get a PSA test every six months, a digital rectal exam once every year, and biopsies and imaging tests every one to three years.

Magnetic resonance imaging (MRI) tests may also be done to determine the risk level of prostate cancer.

Treatment is considered only if your cancer is growing quickly or becoming aggressive.

If you are being treated for prostate cancer, PSA may also be used as a biomarker for how well the treatment is working.