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Free PSA as a Percentage of the Total: Where Do We Go from Here?

Pain Research & Nuffield Department of Anaesthetics, University of Oxford, Oxford Radcliffe Hospital, The Churchill, Oxford OX3 7LJ, UK, Fax +44 1865 226978, e-mail andrew.moore@pru.ox.ac.uk

In this issue of Clinical Chemistry (pp 1588–94), Junker et al. elegantly try to tease out the usefulness of the percentage of free prostate-specific antigen (PSA) (that fraction not bound to proteins like -antichymotrypsin) in making the differential diagnosis of prostate cancer and benign prostatic hyperplasia (BPH). Their approach was to select samples from well-defined patients, 30 with BPH and 50 with cancer, and subject them to analysis by four commercial systems for analyzing the free and total PSA in serum. At a sensitivity of 95%, negative predictive values and the proportion of men with BPH who may be spared prostate biopsy were calculated.

There were differences between the assays. Absolute values reported for control materials with different amounts of complexed PSA varied by factors of 2 or more between the assays, and the proportion of free PSA calculated from control materials was consistently lower in the CIS and DPC methods than in the Boehringer and Hybritech methods. Negative predictive values at 95% sensitivity had confidence intervals that were wide (reflecting the limited number of samples), and those of all four methods overlapped. But the bottom line was that, on this set of samples, three of the four assay systems might prevent 40% or more of men with BPH from having unnecessary (and painful) prostate biopsies; the Hybritch method produced much . . . [Full Text of this Article]

References

The following articles in journals at HighWire Press have cited this article:

				J. Peter, C. Unverzagt, T. N. Krogh, O. Vorm, and W. Hoesel Identification of Precursor Forms of Free Prostate-specific Antigen in Serum of Prostate Cancer Patients by Immunosorption and Mass Spectrometry Cancer Res., February 1, 2001; 61(3): 957 - 962. [Abstract] [Full Text]

				J. Peter, C. Unverzagt, and W. Hoesel Analysis of Free Prostate-specific Antigen (PSA) after Chemical Release from the Complex with {alpha}1-Antichymotrypsin (PSA-ACT) Clin. Chem., April 1, 2000; 46(4): 474 - 482. [Abstract] [Full Text] [PDF]