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Originally published November 2, 2026
Last updated November 2, 2026
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A common method of prostate cancer screening is a blood test that measures your prostate-specific antigen (PSA) level. PSA is a protein produced by both normal prostate cells and prostate cancer cells.
In general, a low PSA level is reassuring, while an elevated PSA level raises suspicion, says Rene Sotelo, MD, a urologist with USC Urology, part of Keck Medicine of USC. “However, PSA alone cannot confirm or rule out prostate cancer,” he says. “Benign prostate enlargement and conditions that cause prostate inflammation can also increase PSA. We therefore interpret the result alongside age, medical and family history and a clinical evaluation.”
Dr. Sotelo answers some common questions about what a low PSA can mean and when you should see a specialist.
According to the American Cancer Society, most men without prostate cancer have PSA levels lower than 4 ng/mL of blood. When the PSA level is between 4 and 10 ng/mL, there’s a 1 in 4 chance of having prostate cancer. When the PSA level is higher than 10 ng/mL, the chance of having prostate cancer is more than 50%.
In someone without a history of prostate cancer, a very low PSA generally is not a problem and does not require treatment to increase it.
However, there is a concern that a low result might create a false sense of security and lead someone to stop the screening appropriate for their age and risk factors.
Additionally, some uncommon, highly aggressive types of prostate cancer produce little PSA. Cancer can be present without a substantial increase in PSA. A low PSA therefore does not completely rule out the disease.
Yes. Finasteride and dutasteride, medications used to treat benign prostate enlargement, can lower PSA by approximately 50%. This reduction typically occurs within six months with finasteride and within three to six months with dutasteride.
Finasteride is also used for hair loss, so patients should tell their doctor if they take it for that reason. The PSA result must be interpreted with the medication and duration of use in mind.
Blood in the urine, recurrent blood in the semen and progressively worsening difficulty urinating warrant medical evaluation.
These symptoms do not necessarily mean cancer. However, a low PSA should not be a reason to ignore them. It is also important to remember that early prostate cancer usually causes no symptoms.
The American Cancer Society’s prostate cancer screening guidelines suggest that men who are at average risk of prostate cancer should have a discussion with their doctor about screening at age 50.
The risk of prostate cancer is higher for individuals with a strong family history of prostate or breast cancer, and for those with African American ancestry — so anyone with those risk factors may benefit from starting screening earlier and adjusting the frequency of testing. They might consider seeking a baseline PSA test between ages 45 and 50, or starting at age 40 if they have other risk factors as well (i.e., multiple first-degree relatives who had prostate cancer at an early age).
Patients with a suspicious prostate examination also require further evaluation, even if their PSA is low. Each individual should discuss these options with their doctor.
It depends on why the PSA was elevated and what has happened between measurements. PSA may decrease when inflammation resolves or because of certain medications. A decrease in PSA alone does not prove that cancer is absent.
During cancer treatment, a declining PSA is generally a favorable sign of response, but it is interpreted alongside the clinical course and imaging studies when appropriate.
It is worth discussing with your doctor, but a rising PSA does not automatically mean cancer. There is no universal dividing line between a “normal” and an “abnormal” PSA.
Physicians review previous results, risk factors and possible temporary causes. The rate at which PSA rises should not be the sole reason to order an MRI or biopsy. However, a confirmed increase, considered alongside other findings, may help determine whether further evaluation or closer follow-up is appropriate.
Yes. During screening, PSA helps estimate risk and guide follow-up. If new symptoms develop, a low PSA does not replace an evaluation of those symptoms.
After radical prostatectomy, we expect PSA to be undetectable. After radiation therapy, it may remain detectable and is interpreted in relation to the lowest level reached after treatment.
A specialist can assess PSA alongside medical and family history, medications, a physical examination and other findings to determine whether monitoring is sufficient or additional testing is needed.
Their expertise helps determine when an MRI, additional tests or a biopsy would be appropriate. The goal is to identify cancers that need attention while avoiding unnecessary procedures. Seeing a specialist does not necessarily mean treatment is needed.
A single result should be interpreted within each person’s medical history. Bringing previous PSA results and sharing information about medications can be helpful.
A low PSA is usually good news, but it is not an absolute guarantee. Patients should continue the follow-up agreed upon with their trusted urologist and seek evaluation if symptoms develop, even if their most recent PSA was low.
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