Parent-to-Metabolite Ratio
Definition
The ratio of an intact drug to its in vivo metabolite in hair, used to distinguish genuine ingestion (which produces both) from external contamination (which deposits mostly parent compound). A reported cocaine-positive case typically requires benzoylecgonine at greater than 5 percent of the cocaine concentration.
- Field
- Hair drug testing
- Distinguishes
- Genuine ingestion from external contamination
- Cocaine threshold example
- Benzoylecgonine > 5% of cocaine concentration
- Matrix
- Hair
Common questions
Why can't parent drug alone in hair prove ingestion?+
External contamination, such as handling drug-contaminated surfaces or environmental exposure, can deposit the parent compound on hair without any of it being metabolized, so parent drug alone does not confirm use.
What does finding metabolite alongside parent drug indicate?+
Metabolites form only through the body's own biotransformation, so their presence at a sufficient ratio to the parent compound supports genuine systemic ingestion rather than surface contamination.
Related terms
- Anagen Phase
- The actively growing phase of the hair follicle, during which the keratinocyte is in contact with the dermal papilla capillary and incorporates...
- Cut-Off Concentration
- The threshold analyte concentration, set by regulatory guidance, above which a specimen is reported as a screen-positive. Choosing the cut-off balances sensitivity...
- Decontamination Wash
- A multi-solvent surface wash (typically dichloromethane, methanol and aqueous buffer) applied before digestion to strip externally deposited drug from the cuticle. The...
- Melanin Binding
- The non-covalent association of basic and lipophilic drugs (cocaine, opiates, amphetamines, nicotine) with melanin granules in the hair cortex. Pigmented (black, brown)...
- Segmental Analysis
- The practice of cutting collected hair into sequential 1 cm lengths from the root end and analysing each segment separately. Each centimetre...