PSA Free

Ratio of fPSA/PSA
More than 0.23

Synonyms: free prostate specific antigen, fPSA, free PSA.
Serum
Red cap

This test is performed only when the total PSA concentration has already been determined. Determining free PSA can provide additional diagnostic information in cases of slightly elevated total PSA concentration (usually recommended to determine free PSA if the total PSA concentration was 2.5–20µg/l). Therefore, both parameters need to be tested again simultaneously: PSA and fPSA (if PSA has already been tested, it still needs to be repeated). The fPSA/PSA ratio sometimes provides additional information in unclear cases. The lower this ratio, the higher the probability of a malignant process. With certain exceptions, the approximate cutoff value (proposed to distinguish malignant from non-malignant processes) is 0.23. Other authors recommend choosing a ratio value of 0.19. If the cutoff value for fPSA/PSA ratio is chosen as 0.23, then the sensitivity of cancer diagnosis is 90%, and specificity is 63%. If 0.19, then – 82% and 82%.

Source | Handbook of Basic Laboratory Tests | Doctor of Medical Sciences Gintaras Zaleskis