Prostate specific antigen (PSA) is a naturally occurring protein made in the prostate gland. Testing for elevated PSA levels can be a useful, but imperfect, tool in screening for prostate cancer.

PSA levels can fluctuate throughout life. Elevated PSA results cannot confirm prostate cancer on their own, but can indicate need for further testing. PSA levels can also help measure how far along prostate cancer is, and whether treatments are having any effect.

This article will break down the role of PSA in the prostate, how testing works, and what PSA looks like in different stages of cancer.

Who can get prostate cancer?

Anyone with a prostate can get prostate cancer. This includes both cisgender men and anyone assigned male at birth. The prostate is usually not removed during any gender-confirming surgeries, as this can cause problems with urination and nerve damage.

The prostate gland is commonly described as “walnut-shaped,” and is located behind the bladder and in front of the rectum. It surrounds the urethra, the tube which passes urine and semen out of the body.

The prostate gland makes a protein called prostate-specific antigen, or PSA. A healthy person’s prostate should circulate a small amount of PSA in their blood.

Several health factors and conditions related to the prostate can cause the gland to produce more PSA than normal.

These include:

  • Prostatitis. This refers to inflammation and swelling in the gland and surrounding areas, often due to bacterial infection. Prostatitis can be very painful.
  • Benign prostatic hyperplasia. Also called prostate enlargement, this condition can cause frequent and strained urination, and increased urination at night, among other symptoms. It is not cancerous.
  • Prostate cancer. This occurs when malignant cells grow uncontrollably in the prostate’s tissues. The gland swells, and isn’t able to function properly. In rare instances, prostate cancer can spread elsewhere in the body. In general, a higher PSA level indicates a higher chance of prostate cancer.
  • Urinary tract infection (UTI). Most urinary tract infections are caused by bacteria. They can occur alongside other health issues in the prostate. A 2020 study found 34.6 percent of prostate cancer patients experienced UTIs.

Certain medications can actually lower PSA as a side effect. This may interfere with prostate cancer screening and the accuracy of a PSA level test.

A 2010 study found nonsteroidal anti-inflammatory drugs (such as Aleve and Advil), statins (drugs that lower cholesterol) and thiazide diuretics (which treat high blood pressure) had a statistically significant impact on PSA levels when taken long term.

Finasteride and dutasteride, medications commonly used to treat male-pattern hair loss and enlarged prostate, also cause reduction in PSA levels.

The level of PSA in your blood can be checked with a simple blood test. A nurse or healthcare worker will draw blood, usually from a vein in your arm, using a needle. The blood is then sent to a lab for analysis.

PSA testing is only one tool in deciding whether further testing is needed. Only a tissue biopsy can definitively diagnose cancer.

If your doctor believes your PSA test results require further investigation, they will likely order a prostate tissue biopsy as the next step.

During this biopsy, your doctor will use a thin needle to take a small sample of tissue from your prostate to be analyzed. This can show the presence of malignant cells. Ultrasound and MRI technology may be used to guide a biopsy.

There is no universal scale for judging PSA levels. Results are usually given in nanograms of PSA per milliliter of blood (ng/mL). According to The National Cancer Institute, a measurement of 4 ng/mL or below used to be marked “normal.” A higher PSA result was seen as irregular, indicating need for prostate biopsy.

However, scientists found this method wasn’t totally reliable. Some men with higher PSA levels have healthy prostates, and some with regular PSA levels can have cancer. This is why PSA level testing is not a perfect method for detecting and diagnosing prostate cancer. But it is an important tool.

Checking PSA levels regularly can help establish a personal baseline. If levels rise over time, this can indicate need for further screening. Repeat testing may also be done if prostatitis is suspected.

If you’re already diagnosed with prostate cancer, regular PSA level testing can track your disease progression, and response to treatment.

Organizing prostate cancer into stages is done to communicate how far along the disease is, and to help plan treatment. Stages range from 1 to 4, with higher numbers indicating more advanced disease.

Prostate cancer, like many other cancers, is described based on the American Joint Committee on Cancer‘s TMN (tumor, metastasis, node) staging system. This staging system is based on the size or extent of the tumor, the number of lymph nodes involved, and whether or not the cancer has spread or metastasized to distant sites or organs.

The cancer’s stage is further determined based on two additional factors: the PSA level and the Gleason scale.

The role of PSA in staging

Prostate cancer causes cells to become malignant and multiply uncontrollably. This can lead to overproduction of PSA, and higher levels of PSA in the bloodstream.

However, some men who have prostate cancer do not exhibit elevated PSA levels. And certain noncancerous conditions, like a prostate infection or benign enlargement, can also cause high PSA levels.

PSA levels are just one factor used in determining the stage of prostate cancer. Another diagnostic tool is called the Gleason scale. This rates the extent of abnormality in your prostate cells after biopsy.

At a certain point in prostate cancer’s late-stage progression, Gleason and PSA become less useful. When a tumor is large enough, doctors no longer need these numbers to predict its growth or malignancy.

Overview of stages

Here’s a breakdown of how prostate cancer staging works per the AJCC’s system. This table shows common symptoms at each stage, and what PSA levels are typically identified:

StageFeatures of cancerPSA level
1Cancer is only on half of prostate and not spreading to surrounding tissues.10 ng/mL or less
2ACancer is found in one half or less of one side of the prostate gland.between 10 and 20 ng/mL
2BCancer is found in one or both sides of the prostate.Less than 20
2CCancer is found in one or both sides of the prostate.Less than 20
3ACancer is found in one or both sides of the prostate.20 or greater
3BCancer is found in one or both sides of the prostate. It has spread to nearby glands, tissues, or organs (such as the rectum and bladder). any PSA
3CCancer is found in one or both sides of the prostate. It has spread to nearby glands, tissues, or organs (such as the rectum and bladder). any PSA
4ACancer is found in one or both sides of the prostate. It has spread to nearby glands, tissues, or organs. The cancer has additionally spread to nearby lymph nodes.any PSA
4B
(final stage)		Cancer is found in one or both sides of the prostate. It has spread to nearby glands, tissues, or organs. Cancer has additionally spread farther to bones or distant lymph nodes.any PSA

Your doctor will weight multiple factors when considering if any given treatment for prostate cancer is your best option.

These include:

  • cancer severity
  • life expectancy
  • impacts on your quality of life
  • your overall functionality, and any coexisting health conditions
  • whether other treatments have been or should be tried first

If the cancer is relatively localized (limited to one area of prostate), it can be treated with:

Should your prostate cancer become more widespread, your doctor may also recommend hormone treatment. This is also called androgen deprivation therapy (ADT).

ADT can be very effective at slowing or stopping cancer growth, but it can cause side effects including lower libido, erectile dysfunction (ED) and fatigue. Additionally, some cancers do not respond to ADT.

Patients who are generally in good health and expected to be functional post-treatment will likely be offered surgery. However, if disease is widespread, extending past the prostate to other tissues and organs, surgery may no longer be an option.

PSA level testing can sometimes result in “false positives” for prostate cancer. This can lead to unnecessary invasive procedures, and create stress about cancer in low-risk individuals.

The 2018 U.S. Preventive Services Task Force made the following conclusions:

  • Men aged 55 to 69 should decide for themselves whether to undergo a PSA level blood test, after talking it over with their doctor.
  • For men over age 70, the potential risks of PSA screening outweigh the benefits.
  • There isn’t conclusive evidence yet that PSA screening prevents prostate cancer deaths.

The CDC explains that older men, Black men, and men with a history of prostate cancer in their family are most at risk of developing it. The majority of cases are diagnosed in men over age 65.

Prostate cancer is one of the most common types of cancer. Statistics from 2016-2018 show that around 12.5 percent of American men will be diagnosed with it in their lifetime.

Multiple diagnostic tools are used together to screen for, and diagnose, prostate cancer. This includes PSA level testing, prostate tissue biopsy, and imaging. These tools are also used to monitor disease progression, and how you’re responding to treatment.

Prostate cancer has a very positive outlook, especially when caught before the final stages. Treatment options have progressed rapidly, and the five-year survival rate for all types of prostate cancer is 97.5 percent.

Talk to your doctor about your risk factors, and to learn more about the pros and cons of PSA level testing.