Free and Total Prostate-specific Antigen in a Screened Population

Objectives: To determine whether the ratio of free to total (F/T) prostate-specific antigen (PSA) can differentiate between men with prostate carcinoma or benign conditions in a screened population.

Subjects And Methods: Total and free serum PSA (measured using Delfia PSA assays, Abbott IMx and Hybritech Tandem E methods) were determined retrospectively in 1726 men aged 55-77 years, in whom 67 prostate carcinomas were detected by screening with a digital rectal examination, transrectal ultrasonography, and total serum PSA level. Predictors for a positive biopsy result were estimated as a function of total PSA, free PSA and the combination of both.

Results: There was an excellent correlation between the Delfia ProStatus, the Abbott IMx and the Hybritech Tandem E assays. Compared with the total serum PSA level, the F/T ratio improved the specificity significantly only in those men with a total PSA of > or = 7 ng/mL. Using the information given by the total and free PSA values, a maximum sensitivity of 75% at a specificity of 74% was obtained for the whole PSA range from 4 to 10 ng/mL; the maximum sensitivity was 79% with a specificity of 71%.

Conclusion: The optimal mathematical combination of free and total serum PSA improves the specificity of total serum PSA level in detecting prostate carcinoma more than the does the F/T PSA ratio.