Percent Free Prostate-Specific Antigen

**Semantic type:** Quantitative Concept

**Definition:** PSA circulates in the blood in two forms: free or attached to a protein molecule. With benign prostate conditions, there is more free PSA, while cancer produces more of the attached form. A more accurate predictor of cancer than either a patient's age or his total PSA level. (from Cancer Information Service)

**Synonyms:** - free PSA