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Cutpoints in Clinical Chemistry: Time for Fundamental Reassessment

Memorial Sloan-Kettering Cancer Center, New York, NY

^aAddress correspondence to this author at: Memorial Sloan-Kettering Cancer Center, 1275 York Avenue Box 213, New York, NY 10021, Fax 1-646-422-2379, E-mail liljah@mskcc.org

The first 300 words of the full text of this article appear below.

When prostate-specific antigen (PSA) testing started to become widespread in the late 1980s, discrepancies between values yielded by different assays became apparent. Elucidation of the various molecular forms of PSA in the blood and other bodily fluids in the early 1990s contributed critical information as to how to avoid these assay-related biases (1). Another important advance was Stamey and coworkers’ design of a novel PSA calibrator (2), which later was endorsed by the WHO. In the last issue of Clinical Chemistry, Jansen and colleagues reported their use of the WHO-endorsed calibrator to examination the recalibration of one widely used PSA assay (3). Jansen et al. (3) report that calibration affects both the likelihood that a man will undergo a biopsy procedure and the likelihood that the biopsy will reveal cancer. This report is a timely reminder that the PSA concentration, as given on a laboratory report, is not a simple statement of a true biological state but is affected by subtle details of laboratory techniques. A man whose PSA increases from 1.9 to 2.4 µg/L over the course of a year would have cause for concern because this sudden increase in PSA exceeds a widely discussed "PSA velocity" cutpoint of 0.35 µg/L per year (4) and thus may be indicative of cancer. As Jansen and coworkers demonstrated, however, such an increase may also be attributable to a change in the assay used to measure PSA.

The main results of the Jansen study focused on a different and more widely used cutpoint as an indication for biopsy, a PSA concentration of 3 or 4 µg/L. The use of this cutpoint reflects contemporary urologic practice, and the authors correctly state that their analyses have important practical implications. We suggest an additional . . . [Full Text of this Article]

For Many Cutpoints the Rationale Is Unknown

Cutpoints Are Often Chosen with Irrational Methods

Cutpoints Are Invariant to Patient Preference

Cutpoints Cannot Include Multiple Pieces of Information

Use of Risk Prediction in Place of Cutpoints

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