Daily Bolus of LR: Urine Tox Screen

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April 13, 2011 by dailybolusoflr

The urine toxicology screen measures the presence of the drug or its measured metabolites.  It is positive for varied durations depending on the drug being measured.  The following are approximate times during which the test will be positive after use of the drug:

·         Amphetamines: 24 to 48 hours

·         Barbiturates: up to 6 weeks

·         Benzodiazepines: up to 3-7 days but up to 6 weeks with high level use

·         Cocaine: 2 to 4 days; up to 10 with heavy use

·         Opiates (including methadone): 1 to 3 days (false positives for methadone have been reported with the sleep aid doxylamine (unisom)

·         Phencyclidine (PCP): 1 to 8 days   (false positives have been reported with the antipsychotic thioridazine)

·         Tetrahydrocannabinol (THC): 6 to 11 weeks with heavy use (this is due to the high lipid solubility of the drug and its storage in fat tissue)



Linda Regan, MD FACEP

Program Director, Emergency Medicine Residency

Johns Hopkins Medical Institutions


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