Prostate-Specific Antigen (PSA) Test

July 1, 2024

This page was reviewed under our medical and editorial policy by Wesley Yip, M.D., assistant professor, Division of Urology and Urologic Oncology, Department of Surgery, City of Hope^® Cancer Center Duarte

The prostate-specific antigen (PSA) test is a blood test that a doctor may order for prostate cancer screening. Men should discuss with a doctor the benefits and possible risks of having a PSA screening to evaluate cancer risk.

The PSA test is also used after diagnosis to monitor responses to prostate cancer treatment.

What Is a PSA?

Cells in the prostate gland make the protein PSA. Although most of it is found in semen, small amounts may travel to the bloodstream, where it may be measured. Increased levels occur in several conditions, such as prostatitis (an inflamed or infected prostate), benign prostatic hyperplasia (BPH/enlarged prostate) and prostate cancer.

PSA Testing for Cancer

PSA levels are used — sometimes along with a digital rectal exam (DRE) — to screen for possible signs of prostate cancer.

• If PSA levels are elevated and there are no other signs of prostate cancer, a doctor may recommend regular PSA testing, along with regular DREs, to check for changes over time, or other workup, such as with a magnetic resonance imaging (MRI) scan.
• If there is a lump found during a DRE or other concerning signs, the doctor may order additional PSA testing, or other tests such as imaging scans, like transrectal ultrasound or MRI, or a biopsy.

PSA levels are also measured after the diagnosis of prostate cancer to see whether the disease may be progressing or whether it has come back (recurred).

How PSA Tests Are Performed

A PSA test is performed on a sample of blood taken from the patient’s arm. The blood is then analyzed in a laboratory, and the results are reported in nanograms per milliliter (ng/mL) of blood. The blood test takes a few moments, and the results are usually available within a few days.

PSA Levels

No set PSA level determines whether a patient has cancer. Some patients with high PSA levels do not have cancer, while others may have low PSA levels and have it. Many doctors accept levels up to 4 ng/mL as normal. Some doctors lower that range to 2.5 to 3.5 ng/mL. Borderline results between 4 and 10 ng/mL may need more investigation. Prostate cancer is more likely with levels above 10 ng/mL.

What Elevated PSA Levels May Mean

Cancer is not the only cause of increased PSA levels. Several factors may affect PSA levels, including those below.

Benign prostatic hyperplasia (BPH): With BPH, the prostate becomes enlarged due to an overgrowth of the prostate tissue.

Prostatitis: Prostatitis develops when the prostate becomes infected or inflamed.

Ejaculation: If patients have had sex or masturbated within 24 hours of the blood test, their PSA level may be slightly higher. Their doctor may suggest abstaining for a couple of days beforehand.

Procedures involving the prostate: Some procedures, such as a prostate biopsy or cystoscopy, may stimulate the prostate, causing a temporary rise in PSA levels. Even a rectal exam has been shown to increase them. If both tests are performed the same day, the blood test should be done first. 

Medications: Taking male hormones such as testosterone or other medications that increase testosterone levels may affect PSA levels.

Bicycle riding: Some studies have linked biking to a temporary rise in PSA levels.

Age: PSA levels naturally rise slowly with age, even with a healthy prostate.

Some medications or supplements lower PSA levels even when the patient has prostate cancer. The patient should tell his doctor about any treatments or medicines, including over-the-counter medications and supplements, he is taking.

If noncancerous causes of the elevated PSA levels have been ruled out, the care team may recommend repeating the PSA test in a few months or ordering other tests.

Understanding PSA Test Results

A screening PSA test measures all forms of PSA in the blood and is called a total PSA. If this level is elevated, the doctor may order additional tests before proceeding with a biopsy. These tests may include those listed below.

PSA density: Patients with larger prostates often have higher levels of PSA. Density is used as a measurement to account for this factor. Ultrasound or MRI measures the prostate’s volume. Density is calculated by dividing the PSA level by the volume. Higher density results are associated more often with prostate cancer.

PSA velocity: PSA velocity is the speed at which the PSA level rises, measured in ng/mL per year. While a slow increase is normal with age, a rapid increase in PSA levels may indicate prostate cancer. Several tests over 12 to 18 months are needed to calculate the rate. This test is more useful for patients with prostate cancer to monitor the cancer’s progression or recurrence.

Percent-free PSA: PSA is found in two forms in the blood. One form, complex PSA, attaches itself to proteins in blood cells. The other, called free PSA, circulates freely in the bloodstream. A percent-free PSA test measures the percentage of free PSA. Results in lower percentages are associated with prostate cancer and may help the doctor decide whether a biopsy is needed.

PSA-related biomarkers: Researchers have developed methods, such as the prostate health index (PHI), IsoPSA^®, 4Kscore^® Test and several others, that combine different PSA values and prostate cancer biomarkers. These tests help predict whether prostate cancer requires treatment and may help the patient avoid unneeded tests with possible health risks.