Segmental Analysis
Definition
The practice of cutting collected hair into sequential 1 cm lengths from the root end and analysing each segment separately. Each centimetre represents approximately one month of growth, so the resulting concentration profile plots drug exposure against time.
- Segment length
- Sequential 1 cm lengths from the root
- Growth rate assumption
- Approximately 1 cm per month
- Output
- Concentration profile of exposure over time
Common questions
What can segmental analysis show that a single bulk hair test cannot?+
It can place drug or poison exposure within an approximate month-by-month window, letting an examiner distinguish a one-off exposure from repeated use, which a single measurement across the whole strand cannot do.
What limits the accuracy of the timeline it produces?+
Individual variation in hair growth rate, cutting position relative to the scalp, and external contamination of the hair surface all introduce uncertainty into how precisely a segment maps to a calendar period.
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)...
- Parent-to-Metabolite Ratio
- The ratio of an intact drug to its in vivo metabolite in hair, used to distinguish genuine ingestion (which produces both) from...