The blood test for prostate cancer measures prostate specific antigen (PSA) levels. Although these tests may help to screen people for prostate cancer, they also have some limitations.

Cancer that starts in the prostate is known as prostate cancer. The prostate is part of the male reproductive system. It is a small gland just below the bladder and in front of the rectum. It helps produce reproductive fluid.

According to the Centers for Disease Control and Prevention (CDC), prostate cancer is the most common cancer in American males after skin cancer. All males are at risk of prostate cancer, with the risk increasing as they age.

Screening is where doctors use tests to look for cancer before it causes symptoms. There is no standard test doctors use to screen people for prostate cancer. However, one prostate cancer screening test is a prostate specific antigen (PSA) blood test.

This article discusses the PSA blood test, and how doctors use it to screen people for prostate cancer. It also explains the test results and limitations.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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The PSA test measures how much PSA is in a person’s blood. PSA is a protein made by cells in the prostate.

Higher levels of PSA in a person’s blood can indicate a higher likelihood that they may have prostate cancer. However, many factors apart from prostate cancer can also affect PSA levels.

During a PSA test, healthcare professionals take a blood sample. They then send the sample to a laboratory for analysis.

Because various factors can affect PSA levels, a doctor interprets the results. They can then decide if a person may need further testing to diagnose prostate cancer or other underlying issues.

Research is ongoing to find ways to make PSA testing more accurate when detecting early prostate cancer.

Learn about prostate cancer.

According to recent guidance from the American Urological Association (AUA), the PSA blood test is the standard screening test for prostate cancer. Healthcare professionals may use other tests to screen for prostate cancer instead of or combined with PSA tests.

PSA tests can be unreliable due to the fact that increased PSA levels can also indicate other conditions, such as infection or inflammation of the prostate. However, they can help indicate that a person may require further testing.

Many tumors that PSA tests detect grow slowly, and are less likely to be life threatening. While evidence is limited as to whether early detection and treatment increases the outlook for prostate cancer, it can still be useful.

Healthcare professionals can discuss the benefits of a PSA test. They may not recommend PSA tests as a screening method for everyone.

PSA test results describe how much PSA is in a person’s blood in nanograms per milliliter (ng/mL).

There is no standard set level for normal PSA blood levels. Different healthcare professionals may decide that different PSA levels indicate if a person requires further testing. According to the American Cancer Society (ACS), doctors consider the cutoff point for a person to need further testing to vary from 2.5–4 ng/mL.

Most males without prostate cancer have a PSA level of less than 4 ng/mL. However, this does not guarantee that a person does not have prostate cancer. People with a PSA level between 4 and 10 ng/mL have around a 1 in 4 chance of having prostate cancer.

Read about the prevalence of prostate cancer.

If a person’s PSA levels are elevated, it may mean that they have prostate cancer. However, many people with elevated PSA levels do not have cancer.

Doctors may recommend a person with elevated PSA levels have further testing. This can include:

A tissue biopsy is the only test that can determine if a person has prostate cancer.

During a biopsy, a healthcare professional takes small samples of a person’s prostate tissue and sends them to a laboratory for examination. This allows a doctor to tell for sure if a person has prostate cancer. It also helps to tell how likely it is that their cancer will grow and spread, and how quickly.

Read about the stages of prostate cancer.

The following factors can affect PSA test results:

  • a person’s age
  • some medical procedures
  • some medications
  • having an enlarged prostate
  • prostate infections

PSA tests may also produce false negative results and false positive results.

False negative results are where people with normal PSA levels have prostate cancer. False positive results are where doctors cannot later detect prostate cancer in people with raised PSA levels.

Individuals should discuss the benefits and limitations of PSA tests for prostate cancer screening with a healthcare professional.

The following are some questions people frequently ask about prostate cancer.

What are the 5 warning signs of prostate cancer?

Five warning signs of prostate cancer include:

  • blood in the urine or semen
  • needing to urinate more frequently, especially at night
  • difficulty with urination, such as a weak or interrupted flow or having trouble completely emptying the bladder
  • pain or a burning sensation during urination
  • pain that doesn’t go away in the back, hips, or pelvis

What is the most accurate test for prostate cancer?

Doctors use tissue biopsies to accurately diagnose if a person has prostate cancer. A biopsy is where a healthcare professional takes small samples of tissue from the prostate for laboratory examination.

The blood test for prostate cancer detects levels of PSA in the blood. If a person has elevated PSA levels, it may indicate they have prostate cancer. Healthcare professionals typically recommend further testing if a person has a high PSA level.

However, PSA tests may falsely indicate a person has prostate cancer or not detect it. Many other factors can also raise a person’s PSA levels.

Healthcare professionals may only recommend a PSA test after discussing the benefits and limitations with them.