Critical aspects related to the interpretation of the free-to-total PSA-ratio.
BACKGROUND
The number of assays available for the measurement of total and free PSA is increasing. As different methods can determine different PSA concentrations as well as different free-to-total PSA ratios in identical serum samples, the cut-offvalue for the ratio still needs to be determined.


METHODS
114 sera from patients with histologically confirmed benign prostatic hyperplasia (BPH; n = 58) and cancer of the prostate (CaP; n = 56) were analyzed with two different assays. Free PSA (free), total PSA (total) and the free-to-total- PSA ratio (ratio) were determined employing Enzym-Test PSA und freies PSA (Boehringer Mannheim, Germany) and Immulite PSA und freies PSA (DPC Biermann, Bad Nauheim, Germany)


RESULTS
The statistical results are tabulated below: [table: see text]


CONCLUSIONS
Direct comparison of the two assays revealed a high statistical correlation (r = 0.94-0.99) for free and total PSA. In contrast, the ratio of the two assays was not as reproducible (r = 0.81-0.83). This result indicates that the reference range for the ratio is dependent on the assay employed and an that uncritical use of an applied reference range can be counter-productive.
Wolff
J M
JM
Department of Urology, RWTH Aachen, Germany.
Stocker
G
G
Borchers
H
H
Haubeck
H
H
Greiling
H
H
Jakse
G
G
D000368:Aged; D000369:Aged, 80 and over; D003937:Diagnosis, Differential; D006801:Humans; D008297:Male; D008875:Middle Aged; D017430:Prostate-Specific Antigen / Q000097:blood*; D011470:Prostatic Hyperplasia / Q000097:blood / Q000175:diagnosis* / Q000473:pathology; D011471:Prostatic Neoplasms / Q000097:blood / Q000175:diagnosis* / Q000473:pathology; D011485:Protein Binding; D011933:Reagent Kits, Diagnostic; D012016:Reference Values; D012044:Regression Analysis; D015203:Reproducibility of Results
D011933:Reagent Kits, Diagnostic; D017430:Prostate-Specific Antigen