Related tests: Total PSA
Clinical significanceClinical indicationsSample typePreparation
Clinical significance
PSA forms complexes with various protease inhibitors, including α2-macroglobulin and α1-antichymotrypsin (ACT); in serum, PSA is mainly in complexed form and only minimally in free form. In prostate cancer, the free fraction generally decreases further; therefore, when total PSA exceeds the limit of 4.0 ng/mL, measuring free PSA and calculating the free PSA/total PSA ratio is indicated to increase the diagnostic specificity of screening. In prostate cancer this ratio tends to be below 20%.
Clinical indications
Prostate cancer screening.
Sample type
The patient must have a blood sample taken.
Preparation
You must fast for at least 8 hours; a small amount of water is allowed.