Determination of the percentage of free prostate-specific antigen helps to avoid unnecessary biopsies in men with normal rectal examinations and total prostate-specific antigen of 4-10 ng/ml.
OBJECTIVE
To assess the usefulness of measuring the percentage of free prostate-specific antigen (PSA) in serum to reduce the number of prostate biopsies in men with serum PSA levels between 4 and 10 ng/ml and benign prostate examinations.


METHODS
The percentage of free PSA (Immulite((R))) in serum was analyzed prospectively in 180 men with benign digital rectal examinations and total PSA serum levels of between 4 and 10 ng/ml. All patients underwent ultrasound-guided sextant prostatic biopsies. Sensitivity, specificity and positive and negative predictive values were calculated as well as the percent of patients in which biopsies could have been avoided for various cutoff values of the percentage of free PSA as an indicator for biopsy. Influence of age in the determination of cut points was evaluated.


RESULTS
Cancer was detected in 22.2% (40/180) of the patients. Mean percentage of free PSA was 13.4% in patients with cancer and 18.9% in patients with benign prostatic hyperplasia (p = 0.001). Using a percentage of free PSA cutoff of 22% or less as a criterion for performing prostatic biopsy would have detected 95% of cancers, avoided 25% of benign biopsies and yielded a positive predictive value of 29% in patients who underwent biopsy. Mean percent of free PSA values increased as mean subject age increased, influencing the calculation of cut points, sensitivity and specificity. Leaving the cut point constant across all age groups will oblige older patients to undergo an increased number of unnecessary biopsies, although allowing for higher sensitivity in younger men.


CONCLUSIONS
Measurement of the percentage of free serum PSA improves specificity of prostate cancer detection in patients with elevated total serum PSA levels and benign prostate examinations. Subject age seemed to influence the determination of optimal cut points.
Martínez-Piñeiro
L
L
Service of Urology, Department of Clinical Biochemistry, La Paz University Hospital, Autonomous University of Madrid, Spain. martinez_pineiro@compuserve.com
Tabernero
A
A
Contreras
T
T
Madero
R
R
Lozano
D
D
López-Tello
J
J
Alonso-Dorrego
J M
JM
Picazo
M L
ML
González Gancedo
P
P
Martínez-Piñeiro
J A
JA
de La Peña
J J
JJ
D000368:Aged; D014408:Biomarkers, Tumor / Q000097:blood*; D001706:Biopsy; D016022:Case-Control Studies; D006801:Humans; D008297:Male; D010808:Physical Examination; D011237:Predictive Value of Tests; D011467:Prostate / Q000473:pathology*; D017430:Prostate-Specific Antigen / Q000097:blood*; D011470:Prostatic Hyperplasia / Q000175:diagnosis; D011471:Prostatic Neoplasms / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology; D012372:ROC Curve; D012007:Rectum; D012680:Sensitivity and Specificity
D014408:Biomarkers, Tumor; D017430:Prostate-Specific Antigen