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Utilization of polyclonal serum prostate specific antigen levels in screening for prostate cancer: a comparison with corresponding monoclonal values.

OBJECTIVES
Prostate specific antigen (PSA) measurement has become increasingly popular as a screening test for prostatic adenocarcinoma. Although this is a sensitive, organ-specific assay, use as a screening tool is hampered by the lack of a clearly defined normal range in older men, frequent elevation of PSA levels by benign processes, and the availability of two different assays, one polyclonal and the other monoclonal, which produce very different values. This study was designed to evaluate the distribution of PSA levels by the Yang and corresponding Hybritech values in patients from the general population.


SUBJECTS AND METHODS
A total of 478 volunteers over 40 years of age underwent serum PSA determination by the Yang polyclonal radioimmunoassay and digital rectal examination. The PSA levels were stratified and the patient distribution analysed.


RESULTS
In 69% of patients, PSA levels were < or = 2.5 ng/ml (proposed normal range for the Yang polyclonal assay). In 89% of patients, PSA levels were < or = 7.3 ng/ml by the polyclonal assay which corresponds approximately to the proposed normal range of 0-4.0 ng/ml by the Hybritech monoclonal assay. Nine per cent of patients fell between 7.4 and 18.4 ng/ml by the polyclonal assay (4.1-10 ng/ml by the monoclonal assay) and 2% had polyclonal PSA levels > 18.4 ng/ml (> 10 ng/ml by the monoclonal assay). Cancer detection rates (influenced by the percentage of patients undergoing biopsy) were 0.3% in patients with polyclonal PSA levels < or = 2.5 ng/ml, 1.2% in patients < or = 7.3 ng/ml, 20.9% between 7.4 and 18.4 ng/ml, and 50% of those > 18.4 ng/ml; the overall cancer detection rate was 3.8%.


CONCLUSIONS
These data support the use of higher PSA levels as a criterion for further evaluation in screening for prostate cancer and establish the frequency distribution of PSA in a screening population when the Yang assay is used.