Age related changes of free and total prostate specific antigen in serum

PSA in serum exists in several molecular forms. The amount of free and total PSA and ratio are discussed to be useful to increase the ability of PSA to distinguish prostate cancer from benign prostatic hyperplasia. Therefore, we tried to characterize the age related changes of free and total PSA in a German rural population.

Serum samples were obtained from 697 men. All study participants were between 20 and 79 years old and had no clinical evidence of prostate cancer by serum PSA, digital rectal examination and transrectal ultrasonography. The sera were kept frozen at -20 degrees C until analysis and were assayed within 3 months after sampling. Free and total PSA values were determined employing a chemiluminescent enzyme immunoassay (Immulite PSA and Freies PSA, DPC Biermann).

Free PSA, total PSA and the free-to-total PSA ratio (f-/t-ratio) demonstrated a correlation with patient age (r = 0.855, p = 0.0141; r = 0.857, p = 0.0137; r = -0.788, p = 0.0352). Employing the median and the 95% percentile the age-specific reference ranges for free and total PSA were calculated. For the f-/t-ratio the median and the interquartile range (i.e. 25th-75th percentile) were calculated.

In confirmation of a recent report, we found a direct correlation of free PSA, total PSA and the f-/t-ratio with age, whereas free and total PSA increases, the f-/t-ratio decreased with advancing age.