What is PSA What is the normal PSA value What is free total PSA

PSA stands for prostate specific antigen. PSA is a chemical produced by prostate cells, both normal and cancerous. PSA is not produced significantly by other cells in the body. Normally, only a small amount of PSA gets into the bloodstream. However, when the prostate is irritated, inflamed, or damaged, such as in prostatitis and prostate cancer, PSA leaks into the bloodstream more easily, causing the level of PSA in the blood to be higher. The normal range is usually 0 to 4.0 ng/mL; however, in younger men a lower range is used (Table 1). The normal range for PSA varies with age and race.

100 QUESTIONS AND ANSWERS ABOUT MEN'S HEALTH Table 1 Age-Adjusted Normal PSA Ranges

PSA that is attached to chemicals (proteins) is bound PSA and PSA that is not attached to proteins is called free PSA.

Bound PSA

PSA attached to the proteins in the bloodstream.

FreePSA

The PSA present that is not bound to proteins. It is often expressed as a ratio of free PSA to total PSA in terms of percent, which is the free PSA divided by the total PSA x 100.

40-49

50-59

60-69

70-79

Normal range (ng/mL)

Reprinted with permission from Oesterling et al. JAMA 1993; 270:860-864. Copyright © American Medical Association.

Once a baseline normal PSA has been obtained, the actual number becomes less important and the rate of change of the PSA over time becomes more important.

PSA is found in two forms in the bloodstream. PSA that is attached to chemicals (proteins) is bound PSA and PSA that is not attached to proteins is called free PSA. The amount of each form is measured, and a ratio of the free PSA to the free plus bound (or total) PSA is calculated.

The PSA present that is not bound to proteins is often expressed as a ratio of free PSA to total PSA. It's expressed as a percentage, which is the free PSA, divided by the total PSA x 100.

The higher this number, the less likely that prostate cancer is present. A free PSA value greater than 14-25%

suggests that the presence of prostate cancer is less likely. This ratio may be helpful in individuals with mildly elevated PSAs in the 4-10 ng/mL range for whom the doctor is deciding whether to perform a prostate biopsy.

PSA density refers to the PSA per gram of prostate tissue and is calculated by dividing the PSA by the calculated prostate volume in grams estimated by transrectal ultrasound. A PSA density > 0.15 is felt to be suggestive of prostate cancer.

PSA velocity refers to the change in PSA level over time. As men get older the prostate tends to enlarge, thus it is expected that the PSA may increase slightly over time. In men with a PSA < 4 ng/ml it is felt that a PSA velocity > 0.35 ng/ml is cause for concern, whereas in men with a total PSA > 4 ng/ml a PSA velocity of > 0.75 ng/ml is cause for concern for the risk of prostate cancer.

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