Preventing false-negatives
Substance abusing individuals could try to avoid detection of illicit drug use by using the following techniques:
- In vivo methods, such as drinking a large amount of water or using herbal products, can lead to false-negative results because of dilution.8
- In vitro adulterants are substances added to urine samples after urination to avoid drug detection. Active ingredients include glutaraldehyde (Clean-X), sodium or potassium nitrate (Klear, Whizzies), pyridinium chlorochromate (Urine Luck), andj (Stealth).9
- Other methods used to avoid drug detection include substituting a urine sample with someone else’s clean urine or adding household products, such as bleach, vinegar, or pipe cleaner.
You can spot and prevent false-negatives by:
Directly observing the patient, which helps to prevent individuals from adding foreign materials or substituting the urine sample.
Visually inspecting the urine helps identify sample tampering. Adding household adulterants can produce unusually bubbly, cloudy, clear, or dark sample.
On-site analyses and laboratory analyses of samples. Commercially sold kits can detect adulterants by on-site analysis, such as Intect 7 and AdultaCheck 4 test strips.9 Simple on-site methods can help discover tampering, such as measuring the urine’s temperature and using pigmented toilet water. The U.S. Substance Abuse and Mental Health Services Administration recommends validity checks during laboratory analysis for all urine samples, including temperature, creatinine, specific gravity, pH, and tests for oxidizing adulterants.10
Considerations
The results of UDS should not be interpreted as absolute. Knowing the sensitivity and specificity of the UDS that your institution uses and the patient’s current medication regimen is valuable in distinguishing between true results and false-positives. False-positives can strain the relationship between patient and provider, thus compromising care. When EIA is positive and patient denies substance use, confirming the result with GC-MS may be a good clinical practice.3 Ordering a GC-MS test can be helpful in situations requiring greater precision, such as in methadone or pain management clinics, to verify if the patient is taking a prescribed medication properly or to rule out illicit exposures with greater certainty.
Acknowledgment
The authors would like to thank Steven Lippmann, MD, for his mentorship, encouragement, and editorial support.