Observations on 'false negative' and 'false positive' rates.

One of the more discouraging trends in the literature of drug testing is the rate at which the toxicology community seems willing to accept imprecision in the use of its technical terms of art. This practice never fails to evoke derision when detected in lay commentary, but I am increasingly struck by the convergence of professional and lay literature in this respect. In the drug testing literature, I am particularly dismayed at the case with which the terms "false positive" and "false negative" are bandied about. My most recent experience with this phenomenon is provided by the March 1990 issue of Forensic Urine Drug Testing, the newsletter provided by AACC to laboratories participating in the Forensic Urine Drug Testing Survey and accreditation program. In that publication, I find on page 4 a presentation of the false positive and false negative error rates of drug-testing laboratories, as revealed by the CAP/AACC Survey. The data shown in tabular array are, to say the least, rather alarming if substantiated. The prospect of false positive rates in excess of 1~ much less 6070, in high-volume workplace urine drug testing programs does not bear contemplation. A careful reading of the text that accompanies the table, however, reveals a very different problem-at least it does to a reader familiar with the history of the AACC survey. It turns out that much of the laboratories' diffieulty attaches to Survey specimens spiked at or below common analytical cutoffs or to specimens whose "corrrect" analysis required reporting rules different from those normally used for workplace drug testing. Given the rather elliptical nature of the Survey instructions to participant labs, itis not terribly surprising to me that a higher-than-usual number of labs got momentarily lost in the turns. I would suggest, however, that this situation has less to do with the laboratories' analytical proficiency in testing workplace urine specimens than it does with their ability to keep up with the twists and turns in the political confrontation between different accreditation agencies. In your own Journal, I have noted a three-part installment on "Further Observations: False Negative EMIT Cannabinoids," "False Negative Rate on EMIT Cannabinoids," and "More on the False Negative Rate for EMIT Cannabinoids" (1,2,3). Now, the EMIT cannabinoids assay is certainly in wide enough use to make its properties of great concern to laboratorians. It is important to all of us that information on technical experiences with the assays …