May 2010 TCPR Correction

Correction: It was brought to our attention by reader Dr. Matthew Tessena of the University of Rochester that some of the cross-reactivities listed in the article, “A Primer on Drug Testing,” from the May 2010 issue of TCPR are no longer relevant with the latest EMIT (enzyme multiplied immunoassay technique) tests.

However, we should have noted other cross-reactivities that were not included in the article. According to Dr. Tessena, the following are the common false positives and false negatives to be aware of in everyday clinical practice:

OPIATE
False positives: poppy seed ingestion from multiple baked goods including muffins, bagels, and danishes (Selavka CM, J Forensic Sci 1991;36:685–696).
False negatives: will not always pick up synthetic opioids such as hydrocodone, hydromorphone, oxycodone, oxymorphone, buprenorphine; never will pick up synthetic opioids methadone, fentanyl, meperidine (Smith ML et al., J Annal Toxicology 1995;19:18–26; Swotinksy R, and Smith D. The Medical Review Officer’s Manual. 4th ed. Beverly Farms, MA: OEM Press; 2010).

AMPHETAMINE
False positives: ephedrine, pseudoephedrine, phenterimine, and promethazine, also MDMA "ecstasy," vicks vapor inhaler (l-methamphetamine) (Swotinksy & Smith).

THC
False positive: dronabinol (Gustafson RA et al., Clin Chemistry 2003;49:1114–1124).

PCP
False positive: dextromethorphan; no false negatives (Schier J, J of Emerg Med 2000;18:379–381).

COCAINE
False positive: topical local anesthetic called TAC (tetracaine, adrenaline, cocaine) used in nasal and eye surgery contains cocaine. Can be mistaken for illicit cocaine use (Schwartz RH et al., Otolaryng Head Neck Surg 1990;102(2):200–210).

In addition, in the chart of Available Drug Tests, the detection window for urine was listed as six to 24 hours. In actuality, the window is closer to three to four days, except for alcohol, which is eight to 12 hours.