PHI, The Prostate Health Index Blood Test
Percent free prostate-specific antigen (PSA) is a measurement used in prostate cancer screening to provide additional information over and above that provided by the total PSA value alone about the likelihood of prostate cancer. PSA is a protein produced by the prostate gland, and it exists in the blood in two main forms: bound to other proteins (complexed PSA) and free-floating (free PSA).
The percent free PSA is the ratio of free PSA to total PSA (both free and bound PSA) multiplied by 100. It reflects the extent to which increased total PSA levels are due to benign causes, such as benign prostate enlargement (BPH) or inflammation in the prostate (prostatitis). Higher percent free PSA levels (greater than 25%) are favorable (i.e., more likely to be associated with benign causes) while lower percent free levels (lower than 10%) are more likely to be associated with prostate cancer. A large national clinical trial (see below) has shown that the percent free PSA in a screening population correlates with the long-term prostate-cancer-specific death rate.
A newer blood test called the Prostate Health Index (PHI) measures a third form of PSA called “minus-2- proPSA,” often abbreviated as “pro-PSA.” ProPSA, when combined with the free and total PSA measurements, in the mathematic formula PHI provides an even more accurate risk assessment for the presence of prostate cancer and also its more aggressive forms.
Dr. Catalona led the pivotal multi- institutional “pivotal” studies that achieved approval of the total PSA, free PSA, and PHI blood tests by the US Food and Drug Administration (FDA).
