What is the Difference Between Free PSA and Total PSA

The key difference between free PSA and total PSA is that free PSA is only the amount of freely floating prostate-specific antigen in the bloodstream while total PSA is the amount of both freely floating prostate-specific antigen in the bloodstream and the prostate-specific antigen bound to other proteins.

Prostate-specific antigen (PSA), also known as gamma-seminoprotein or kallikrein-3, is a glycoprotein enzyme encoded by the KLK3 gene. Epithelial cells of the prostate gland secrete prostate-specific antigens. PSA is produced for the ejaculate. PSA liquefies semen in the seminal coagulum and allows sperms to swim freely. This allows the entry of sperms into the uterus. PSA can freely float in the bloodstream. This form is called the unbound or free PSA. On the other hand, the bound PSA is associated with other proteins in the body. The total PSA level refers to the amount of both bound and unbound forms of prostate-specific antigen.

CONTENTS

1. Overview and Key Difference
2. What is Free PSA 
3. What is Total PSA
4. Similarities – Free PSA and Total PSA
5. Free PSA vs Total PSA in Tabular Form
6. Summary – Free PSA vs Total PSA

What is Free PSA?

Free PSA is the amount of freely floating prostate-specific antigen in the bloodstream. Most PSA in the blood is bound to serum proteins. Only a small amount is not bound to serum proteins. This PSA is called the free PSA. A free PSA test can measure the amount of free PSA level in the body. Moreover, free PSA level is very important to determine the likely hood of prostate cancer in men. Normally, free PSA levels are often higher in those with non-cancerous conditions of the prostate. However, free PSA levels are lower in those with prostate cancer.

If a person has a total PSA level between 4 to 10 ng/mL, doctors may test the blood for free PSA levels. A ratio of the amount of free PSA to the total PSA above 25% is considered normal. The risk of prostate cancer increases if the free PSA to total PSA ratio is less than 25%. Some doctors may also recommend a prostate biopsy if a patient has this ratio of 18% or less.

What is Total PSA?

Total PSA is the amount of both freely floating prostate-specific antigen in the bloodstream and the prostate-specific antigen bound to other proteins. The total PSA test measures both bound and unbound forms of PSA in the body by using blood. The results are usually reported as nanograms of PSA per milliliter of blood.

The doctors may consider a total PSA level of 4 ng/mL and lower as normal. Therefore, if a person has a PSA level above 4 ng/mL the doctors would often recommend a prostate biopsy to determine whether the prostate cancer is present. However, total PSA is a complicating factor when determining prostate cancer. This is because recent studies have shown some men with total PSA levels below 4 ng/mL have prostate cancer. Furthermore, some patients that use drugs such as finasteride and dutasteride for the treatment of BPH may have lower PSA levels due to the effects of these drugs.

What are the Similarities Between Free PSA and Total PSA?

  • Free PSA and Total PSA both refer to a specific glycoprotein enzyme called prostate-specific antigen that is produced from epithelial cells of the prostate gland.
  • Both free PSA and total PSA are more important factors for men than women.
  • They can be measured through specific tests by using blood.
  • Both free PSA and total PSA are compulsory to determine the free PSA to total PSA ratio.
  • The amounts of both free PSA and total PSA are important to determine the risk of prostate cancer in men and the subsequent need for prostate biopsy.

What is the Difference Between Free PSA and Total PSA?

Free PSA is only the amount of freely floating prostate-specific antigen in the bloodstream, while total PSA is the amount of both freely floating prostate-specific antigen in the bloodstream and the prostate-specific antigen bound to other proteins. Thus, this is the key difference between free PSA and total PSA. Furthermore, free PSA level is often higher in those with non-cancerous conditions of the prostate. But total PSA is often less than 4 ng/mL in those with non-cancerous conditions of the prostate.

The below infographic presents the differences between free PSA and total PSA in tabular form for side by side comparison.

Summary – Free PSA vs Total PSA

Prostate-specific antigen (PSA) is a glycoprotein enzyme produced from the prostate gland. PSA can freely float in the bloodstream or can be bound to serum proteins. Free PSA refers to the freely floating prostate-specific antigen in the bloodstream. Total PSA refers to the amount of both freely floating prostate-specific antigen in the bloodstream and the prostate-specific antigen bound to other proteins. So, this is the summary of the difference between free PSA and total PSA.