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Tests for PSA and free PSA are not all currently standardized, which can create several issues:
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Free PSA testing. PSA and free PSA results must be calibrated to each other to have validity, since free PSA is expressed as a percentage of total PSA. For accurate measurement of free PSA, the total PSA and free PSA tests should be by the same manufacturer. One way to accomplish this is by using Beckman Coulter’s Hybritech PSA and free PSA tests.
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Serial measurement of PSA. The rate at which a man's PSA rises over time is called PSA velocity. Some studies have linked PSA velocity to prostate cancer, even if the total PSA value is well below the biopsy cutoff. When employed for the management of prostate cancer patients, serial measurements of PSA are useful in detecting residual tumor or recurrent cancer following radical prostatectomy or other treatments. Moreover, PSA may serve as an accurate marker for monitoring advancing clinical stage in untreated patients, as well as assessing response to therapy. Therefore, serial measurement of PSA concentrations can be an important tool in monitoring patients with prostate cancer and in determining the potential and actual effectiveness of surgery or other therapies. Because PSA tests are not standardized, it is important to get each year’s PSA test performed at the same lab using the same test by the same manufacturer. (NACB Practice Guidelines and Recommendations for Use of Tumor Markers in the Clinic (2005 draft). Section3B, Use of Tumor Markers in Prostate Cancer, H. Lilja, et.al).
For more information on standardization, click here.
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