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Letters |
Departments of
1
Clinical Biochemistry, and
2
Urology, Grampian University Hospitals Trust, Aberdeen AB25 2ZD, United Kingdom
a Author for correspondence. Fax 011-44-01224-694378; e-mail b.l.croal{at}abdn.ac.uk
To the Editor:
Jung et al. (1) reported an apparent gap between
total serum prostate-specific antigen (t-PSA) and the sum of free PSA
(f-PSA) plus 
1-antichymotrypsin-PSA (ACT-PSA)
in patients with prostate carcinoma (PCa) but not in those with benign
prostatic hypertrophy (BPH). The gap may be attributable to a variety
of technical artifacts such as different recognition of multiple forms
of f-PSA or t-PSA in the two groups of patients or the lack of
equimolarity of the tests used (1). Of more interest,
however, is the suggestion by the authors that the appearance of this
"PSA gap" reflects an increase in minor PSA complexes in PCa
patients that their assay for ACT-PSA does not detect. Indeed, they
suggest that such an observation contradicts the high expectations
(2) for the determination of ACT-PSA or the ratio of ACT-PSA
to t-PSA to improve the differentiation between PCa and BPH.
The authors refer to a novel approach to the measurement of complexed forms of PSA (3) as a possible solution to the potential problem of minor PSA forms. This complexed PSA (c-PSA) assay is now available commercially for the Bayer Immuno-1 automated immunochemistry analyzer (Bayer Diagnostics). We recently used this assay along with measurements of t-PSA (Bayer Immuno-1), f-PSA (Abbott IMx; Abbott Diagnostics), and the ratio of f-PSA to t-PSA (Abbott IMx, both assays) on a prospective basis in men referred to a hospital urology clinic with t-PSA measurements between 3.0 and 22.0 µg/L. Of the 79 consecutive patients assessed to date, 21 (27%) were diagnosed with PCa by a combination of clinical presentation, digital rectal examination, prostatic volume, and transrectal ultrasound-guided prostatic biopsy (all patients). We found no gap between t-PSA (Bayer Immuno-1 assay) and the sum of f-PSA (Abbott IMx assay) and c-PSA (Bayer Immuno-1 assay) in patients with PCa or BPH. The sum of f-PSA and c-PSA was 100.6% (SD, 7.6%) of t-PSA in the BPH patients and 100.5% (SD, 6.2%) in the PCa patients.
We believe, therefore, that our data showing the lack of a PSA gap in both PCa and BPH patients, along with the observations of Jung et al. (1), may help solve the conundrum of why ACT-PSA does not perform as well as predicted.
References
1-antichymotrypsin-prostate-specific antigen in patients with prostate carcinoma but not in those with benign prostate hyperplasia. Clin Chem 1999;45:422-424.
1-antichymotrypsin complex for the screening and management of prostate cancer. J Clin Lab Anal 1998;12:32-40.
[Web of Science][Medline]
[Order article via Infotrieve]
a Author for correspondence. Fax 49-30-2802-1402; e-mail klaus.jung{at}charite.de
Departments of
3
Urology and,
4
Laboratory Medicine, University Hospital Charité, Humboldt University Berlin, Schumannstrasse 20/21, D-10098 Berlin, Germany
To the Editor:
Our observation of a prostate-specific antigen (PSA) gap in the
serum of patients with prostate carcinoma (PCa) and the assumption of
the increased occurrence of minor PSA forms in serum may explain the
better discrimination between PCa and benign prostatic hyperplasia
(BPH) patients by the free/total PSA ratio compared with the
determination of the 1-antichymotrypsin-PSA
complex or the ratio of
1-antichymotrypsin-PSA to total PSA
that we observed in 112 untreated patients with PCa and in 34 patients
with BPH (1). However, as pointed out in that report and in
Ref. (2), we cannot exclude all possible technical reasons
for the PSA gap discrepancies between BPH and PCa patients (e.g.,
calibration of the assays, different recognition of the multiple forms
of free PSA or total PSA in both groups, or lack of equimolarity),
although we paid particular attention to this problem. It should be
mentioned that Espana et al. (3), using homemade
immunoassays for the determination of total PSA and
1-antichymotrypsin-PSA, recently found better
discrimination with the ratio of
1-antichymotrypsin-PSA to total PSA than with
the ratio of free to total PSA. Therefore, at present, our results and
the mentioned contradictory data should only draw the attention of
clinical chemists and physicians to the fact that there are possible
biological rather than analytical reasons that contradict the high
expectations placed on the determination of
1-antichymotrypsin-PSA (4). It is
obvious that both basic experiments and clinical studies are necessary
to solve the whole problem. We hope that a recently performed
multicenter study using a newly developed
1-antichymotrypsin-PSA assay with changed
architecture may help clarify this issue.
References
1-antichymotrypsin-PSA complex in serum does not improve the differentiation between benign prostatic hyperplasia and prostate cancer compared to total PSA and percentage free PSA. Urology 1999;53:1160-1168.
[Web of Science][Medline]
[Order article via Infotrieve]
1-antichymotrypsin-prostate-specific antigen in patients with prostate carcinoma but not in those with benign prostate hyperplasia. Clin Chem 1999;45:422-425.
1-antichymotrypsin complex for the screening and management of prostate cancer. J Clin Lab Anal 1998;12:32-40.
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