Abstract
Introduction: Though recent research from the last decade has led to a harmonization of results for free and total PSA, we still have to accept variation between assays regarding recovery. Surveys held in 2002 and 2003 in The Netherlands show differences up till 20-25% for total PSA and even more for free PSA based on recovery values, differences that may influence clinical decision making. In this study we have tried to answer the question whether or not deviations from equimolarity play a role as contribution to the differences in PSA values. To that end we have compared three state-of-the-art assays for PSA with samples coming from an ongoing screening study for prostate cancer (ERSPC).
Results: In total 199 serum samples were analyzed for free and total PSA by applying Beckman, PerkinElmer-Wallac and Roche. Excellent correlations were found between all assays for total PSA and minor correlations for free PSA. Access and E170 proved to differ by 6-7% for total PSA (Access being the highest) while Access and Prostatus were identical, statistically speaking. For free PSA the differences were 4% for the comparison Access and E170 and 11% for Access and Prostatus. A division of the whole collection into two groups wit a lower and a higher concentration free PSA didn't show any difference in regression line for total PSA with Access and E170 while Access and Prostatus differed by 3-4%. Furthermore, a considerable spread was found in all free PSA comparisons.
Conclusions:
1. All assays proved to measure total PSA more or less equimolarly. We only found very small differences in the Access-Prostatus comparison with two sample groups based on a low and high free PSA concentration. These results show that limited differences in equimolarity cannot explain the differences in recovery of total PSA as seen in surveys.
2. We found differences in recovery for free PSA (though limited) and spread in the results. This means in our view that care must be taken in using free/total PSA values in clinical decision making. Measuring free and total PSA with assays from two different manufacturers should be avoided.
| Translated title of the contribution | On the equimolarity of prostate-specific antigen |
|---|---|
| Original language | Dutch |
| Pages (from-to) | 42-48 |
| Number of pages | 7 |
| Journal | Nederlands Tijdschrift voor Klinische Chemie en Laboratoriumgeneeskunde |
| Volume | 30 |
| Issue number | 1 |
| Publication status | Published - Jan 2005 |
