Understanding Your Prostate-Specific Antigen (PSA) Result

Prostate-specific antigen, or PSA, is a protein made by cells in the prostate gland. A small amount normally passes into the blood, where it can be measured by a blood test and reported as a number in nanograms per milliliter (ng/mL). Both normal prostate cells and prostate cancer cells make PSA, so the level can rise when cancer is present, but it can also rise for many non-cancerous reasons. For this reason, PSA is not a simple yes-or-no test for cancer. It is one piece of information used, along with other findings, to decide whether further testing is needed and to follow a known prostate condition over time.

This article explains what the PSA test measures, what your result may mean, what can raise or lower PSA apart from cancer, and how PSA is used both to investigate a raised level and to monitor prostate cancer after diagnosis.

The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown here. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal result with your doctor.

What does the PSA test measure?

The PSA test measures the amount of prostate-specific antigen in the blood. PSA is a protein produced by the gland cells of the prostate, and its normal job is to help keep semen in a liquid form. Because PSA is made by prostate cells whether they are healthy or cancerous, the test does not by itself tell the difference between cancer and a non-cancerous prostate condition. A higher PSA level means there is a higher chance that something is going on in the prostate, which may be cancer or may be a benign condition, and further information is needed to tell which.

How is the PSA test performed?

PSA is measured from a small blood sample drawn from a vein, and no fasting is required. A few everyday factors can temporarily raise the level, so to avoid a misleading result, doctors often suggest waiting a couple of days after ejaculation, vigorous cycling, or a prostate examination before the blood is drawn. It is also important to tell the person ordering the test if you take a medication for an enlarged prostate, because some of these lower PSA and change how the result is interpreted. Because PSA is often followed over time, having the test done at the same laboratory helps make the trend more reliable.

What do the results mean?

There is no single PSA level that cleanly separates cancer from no cancer, which is the most important thing to understand about the result. The chance of finding prostate cancer rises gradually as PSA rises, rather than switching on at one number. The points below explain how a PSA result is generally interpreted.

There is no strict normal cutoff — A level below about 4 ng/mL has traditionally been considered typical, but prostate cancer can occur at lower levels, and many men with higher levels do not have cancer. The number is a guide, not a diagnosis.
Age and prostate size matter — The prostate normally enlarges with age, and a larger prostate produces more PSA. A level that would be unusual in a younger man can be expected in an older man with an enlarged prostate.
A single high result is often repeated — Because everyday factors and temporary conditions can raise PSA, one elevated value is commonly rechecked before anything further is done. Many repeated values return to normal.
The trend over time is important — A PSA that rises steadily across several measurements is more concerning than a single higher-than-expected value, and doctors pay close attention to the pattern.
Free PSA can add information — When the total PSA is in a borderline range, the laboratory can also measure the free PSA, the portion not bound to other proteins. A lower percentage of free PSA is associated with a higher chance of cancer and can help decide whether more testing is needed.

Across all of these points, a PSA result guides the decision about what to do next rather than providing a diagnosis on its own. Only a biopsy, in which small samples of prostate tissue are examined under a microscope, can confirm whether cancer is present.

What can raise or lower PSA besides cancer?

Many non-cancerous factors change the PSA level, which is why a raised result is interpreted carefully rather than taken as proof of cancer. Common causes of a higher PSA include benign prostatic hyperplasia (non-cancerous enlargement of the prostate), inflammation or infection of the prostate (prostatitis), a urinary tract infection, recent ejaculation, a recent prostate examination or procedure, catheter placement, and vigorous cycling. Age also raises PSA gradually as the prostate enlarges.

Some factors lower PSA. The medications used to shrink an enlarged prostate, called 5-alpha-reductase inhibitors (finasteride and dutasteride), reduce PSA by roughly half. If you take one of these, your doctor will take this into account when reading your result, often by doubling the measured value. Because so many factors can move the number in either direction, a single PSA result is always considered together with your history and, when needed, repeated before any next step.

What happens if your PSA is high?

A raised PSA usually leads to a series of steps rather than straight to a biopsy, and the aim is to work out how likely a significant prostate cancer is before deciding whether a biopsy is worthwhile. In most cases, the first step is simply to repeat the PSA, because a single elevated value often returns to normal. If the PSA remains raised, the next steps may include an MRI of the prostate and, in some situations, a secondary blood or urine test (such as free PSA, the 4Kscore, or the Prostate Health Index) that refines the estimate of risk. These tests help identify who is likely to benefit from a biopsy and who can safely avoid one.

If the overall picture still suggests a meaningful chance of cancer, a prostate biopsy is considered. During a biopsy, small samples of prostate tissue are removed and examined under a microscope. If cancer is found, the pathologist assigns a Gleason score and Grade Group, which describe how the cancer cells look and help predict how the cancer is likely to behave. You can read more in our article on prostatic adenocarcinoma, the most common type of prostate cancer. Whether to take each of these steps is a decision you make with your doctor, based on your PSA pattern, other test results, and your preferences.

Using PSA to monitor prostate cancer

Beyond investigating a raised level, PSA is one of the main tools for following prostate cancer after it has been diagnosed or treated. How it is used depends on the situation.

Active surveillance — For low-risk prostate cancer, many men choose careful monitoring instead of immediate treatment. PSA is measured at regular intervals, along with periodic MRI and repeat biopsy, to watch for any sign that the cancer is becoming more active. A rising PSA may prompt a change from monitoring to treatment.
After surgery to remove the prostate — After a radical prostatectomy, PSA should fall to a very low or undetectable level, usually below 0.1 ng/mL, because the gland that makes PSA has been removed. A PSA that begins to rise afterward, called a biochemical recurrence, can be an early sign that some cancer cells remain, and it guides the discussion about further treatment.
After radiation therapy — The prostate is not removed with radiation, so PSA falls slowly to a low point (the nadir) rather than becoming undetectable. A rise of about 2 ng/mL above the lowest level reached is generally used to define recurrence. A small, temporary rise in PSA, called a PSA bounce, can also occur after radiation and does not necessarily mean the cancer has returned.

In each of these situations, the trend in PSA over time is what matters most, and your care team interprets it alongside your other findings to guide decisions rather than acting on a single value.

Questions to ask your doctor

What is my PSA level, and how does it compare to my previous results?
Is my PSA being used for screening, to investigate a symptom, or to monitor a known prostate condition?
Could a non-cancerous cause explain my raised PSA?
Do I take any medication that could be affecting my PSA level?
Should my PSA be repeated before any further testing, and if so, when?
Would an MRI or a secondary test be helpful before deciding on a biopsy?
Based on my PSA and other findings, do you recommend a prostate biopsy?
If I am on active surveillance, how often will my PSA be checked, and what change would prompt treatment?
After my treatment, what PSA level would be expected, and what rise would concern you?
Should my PSA always be measured at the same laboratory to track the trend?