Utility and reliability of emergency toxicologic testing.

Emergency physicians using toxicologic testing should learn the capabilities of their laboratories: What is detectable? What is not? What is the expected turnaround time? Do pharmacologic relationships exist? In ordering test requests, the laboratory should allow the physician to order limited test combinations, and the physician can assist the laboratory in the search for unknowns by indicating the running diagnosis and suspected drugs. Only a few drugs require quantitation in serum in order to assist in therapeutic decisions. Urine drug screening is useful in documenting intoxications due to drugs and frequently demonstrates more drugs or drugs other than those clinically expected. The impact of findings from emergency drug screening upon diagnosis and therapy appears to be low. Although comprehensive drug screening in the emergency setting has a better positive predictive value ("rule-in") than negative predictive value, toxicologic screening may be useful as a "rule-out" test in other diagnostic applications of lower prior probability. Future directions in laboratory diagnosis of the intoxicated patient are likely to include growth in new immunoassays with limited applications, but with rapid turnaround within the Emergency Department. Also, with improvements in technology, screening of serum drugs will become more common, including the discovery of more quantitative relationships between serum concentration and toxic effects.