Prostate-Specific Antigen (PSA) Test: Definition & Procedure

Instructor: Taormina Lepore

Taormina has taught advanced high school biology, is a science museum educator, and has a Master's degree in museum paleontology.

The detection of prostate-specific antigen (PSA) can mean the difference between life and death in patients at risk for prostate cancer. So why is the PSA test under scrutiny? In this lesson, we'll define the prostate-specific antigen test and explain its procedure.

Prostate-Specific Antigen Test Definition

If you are biologically male, or know anyone who is - odds are, you do! - then listen up: this could save your life, or the life of someone you care about. Prostate cancer is the most common tumor in men in the United States, with risk for prostate cancer increasing up to 70 percent in men over 80 years of age.

But there are ways to detect and combat prostate cancer. Early detection is key, and the prostate-specific antigen test is one of two main ways your doctor can test for a risk of prostate cancer. The prostate-specific antigen test involves looking at a patient's blood to detect the presence of an antigen, a protein that indicates whether the prostate is infected or otherwise in poor health. This antigen is normally found in semen and is also present in low levels in the blood. Having higher than 4.0 nanograms of antigen per milliliter of blood can indicate the possible presence of prostate cancer. However, as we'll discuss below, this reading can sometimes lead to false positives or false negatives, and a biopsy, or sample of potentially cancerous tissue, is usually needed to make a final diagnosis.

A normal and an enlarged prostate

The prostate is a glandular organ located just below the bladder and adjacent to the rectum. When the prostate becomes cancerous, a doctor can detect malignant, or dangerous, tumors, as well as benign, or harmless tumors, by performing a digital rectal exam. This exam involves the insertion of a gloved finger into the anus to manually feel whether the prostate has any lumps, or is unhealthily enlarged for other reasons, such as infection.

The least invasive test for the risk of prostate cancer is the prostate-specific antigen test, which can be used to correlate the results of a digital rectal exam, or in place of a digital rectal exam. Typically both are used in conjunction with one another to detect a risk for cancer. If the risk is deemed significant, a biopsy can be undertaken to make a final determination of the presence of cancer. Using these three tests, a doctor can determine the diagnosis of prostate cancer, and together with the patient, a treatment plan can be laid out.

Prostate-Specific Antigen Test Procedure

The procedure for the prostate-specific antigen test is simple. A technician will take a small sample of blood, usually from the arm. This sample will then be tested for the presence of prostate-specific antigen, the marker protein that can help determine prostate health.

A blood sample will be tested for the presence of a prostate-specific antigen.
blood test

The prostate-specific antigen test can produce false negative or false positive results. That is, it could indicate high or low levels of the antigen, which may or may not actually correlate to the presence of prostate cancer. It can be unsettling to receive a positive antigen test, only to find out through biopsy and digital screening that you do not have prostate cancer. On the other hand, the test can provide a false sense of security if it comes back negative.

Is It Necessary?

Although the decision to have the prostate-specific antigen test is ultimately up to men and their doctors, several organizations have made recommendations against the test. Here are several reasons why:

  • It could produce false positives.
  • It could produce false negatives.
  • Older men may not need to be screened.
  • High PSA could be the result of a non-cancerous infection.
  • PSA normally increases with age.
  • Certain medications can lower PSA levels.

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