Toxicology

Lack Specificity

Drug classes vs. individual drugs

Opiates vs 6-monoacetylmorphine (heroin metabolite)

Cross Reactivity

High concentrations of other drugs can yield false positives

DRI Methadone EIA false positive with Tapentadol and metabolites

Lack Sensitivity

Cutoffs typically lower

Opiate cutoff = 300 ng/mL vs 50 ng/mL

Not Comprehensive

Covers approx. 20 drug classes and without focus on metabolites

Detection of noroxycodone (oxycodone metabolite) would indicate biological metabolism, not spiking of oxycodone into the sample

Semi-quantitative at best

1. Patient is compliant and took the prescription as directed
2. Patient added drug to the urine after collection
3. Patient took one dose prior to collection
4. Patient took another drug which cross- reacts with the test, i.e. a false-positive

Pseudoephedrine can give a “Positive” result for an amphetamine screening test

1. Patient is not compliant
2. Patient did not follow dosing regimen
   • Less frequent or lower dose
3. Drug present but below the cutoff
   • Dilute or adulterated urine
   • False-negative
4. Test does not react with drug of interest
   • Appropriately targeted test may not be available
5. Altered pharmacokinetic variables
   • Ultra-fast metabolizer – no parent drug present, only me tabolite
   • Poor drug absorption