Why determine only the total prostate-specific antigen, if the free-to-total ratio contains the information?

Ann Clin Biochem 2008;45:270-274
© 2008 Association for Clinical Biochemistry


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Original Articles

Daniëlle Berty Petra Eekers1,
Andrea Laschet2,
Monique de Groot3,
Erik Roelofs4,
Arnold Kester5,
Karl Delaere6,
Philippe Lambin4,
Francis van Gils4,
Marius Nap7 and
Joop ten Kate8

1 Dr Bernard Verbeeten Institute, Tilburg, The Netherlands;
2 Department of Clinical Chemistry, Atrium Medical Centre, Heerlen, The Netherlands;
3 Department of Clinical Chemistry, Amphia Hospital, Breda, The Netherlands;
4 Maastricht Radiation Oncology, Maastricht, The Netherlands;
5 Department of Methodology and Statistics, Maastricht University, Maastricht, The Netherlands;
6 Department of Urology;
7 Department of Pathology, Atrium Medical Centre, Heerlen, The Netherlands;
8 Department of Clinical Chemistry, Maasland Hospital, Sittard, The Netherlands

Corresponding author: Dr Daniëlle Berty Petra Eekers. Email: eekers.d{at}bvi.nl

Background: Total prostate-specific antigen (tPSA) is the best availabletest for the detection of prostate cancer but it lacks specificity.The free-to-total ratio (F/T ratio) is used to increase specificityin the range of tPSA of 4–10 µg/L.

Materials and methods: Four hundred and seven biopsy results and quantitative tPSAand F/T ratio data were combined. Using the histological determination,normal/hyperplasia versus malignant as a gold standard, receiveroperating characteristic (ROC) curves as well as the areas underthe curve (AUC) for tPSA and F/T ratio were determined. Thedifferences between the two AUCs were considered for varioustPSA ranges and specificities of F/T ratio and tPSA were calculated.

Results: In the total group, there was a gain of specificity of 11% (from23% to 34%) when the sensitivity was 92% (using a cut-off >0.28for the F/T ratio and a cut-off >4 µg/L for tPSA).When considering the group of patients for which the F/T ratiois currently used (4–10 µg/L), the gain of specificitywas 27% (from 2% to 29%). This implicates that the number ofunnecessary biopsies taken will be reduced by 27%. Moreover,the AUC of the F/T ratio was significantly higher at an evenbroader range of tPSA, i.e. up to 40 µg/L.

Conclusions: This study demonstrates that the F/T ratio has better diagnosticperformance than tPSA, not only in the grey zone of tPSA, butalso outside the grey zone, i.e. up to 40 µg/L.

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