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what are the advantages of urine analysis?
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what are the disadvantages of urine analysis?
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most drugs or metabolites of drugs are excreted into the urine at high concentrations (detection is indicative of recent exposure (1-3 days))
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samples can be tampered with (adulterated, substituted, or diluted, & collection requires strict supervision)
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collection of samples is non-invasive
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surveillance window is short (1-3 days), meaning infrequent use is not detected by random testing & screening can be delayed to avoid detection
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urine is not a complex matrix, so sample preparation is minimal
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consumption of large volumes of water may dilute urine & avoid detection
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analytical procedures are well-established for common drugs (analysis can be automated & is cheap)
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drug concentrations in spot samples cannot be related to intensity of drug use (cannot distinguish between light, moderate, or heavy use)
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what is the main ways drugs or metabolites are incorporated into the hair?
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what does the extent of incorporation depend on?
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how can incorporation of the drug into the hair by augmented?
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what are some other ways drugs or metabolites can be incorporated into the hair?
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blood supply (endogenous source): ingested drug -> blood -> hair root -> hair shaft (via passive diffusion) |
molecular size & structure of the drug
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binding of the drug to melanin (hair colour)
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sweat (exogenous source): excreted drug -> sweat in scalp -> hair (via absorption) |
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concentration gradient (blood:hair:root)
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lipid solubility of the drug
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binding of the drug to keratin (sulphydryl groups)
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absorption via external contamination from the environment (e.g. exhaled cannabis)
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ratio of ionised;unionised forms of the drug (pKa of the drug)
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what are some drugs commonly analysed in hair?
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opiates (heroin, morphine, codeine), PCP, cannabis
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cocaine, amphetamine, nicotine
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barbiturates, benzodiazepines, anabolic steroids, industrial toxins (organic not metals)
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what are the five basic steps involved in analysis of hair for drugs?
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what do each of these steps involve?
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1. sample collection
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collecting the hair from the head
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2. decontamination
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washing the hair using a phosphate buffer, detergent (including shampoo), or surfactants
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3. preparation of the hair sample
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pulverisation or segmentation of the hair
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4. extraction of the drug molecules
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using organic solvents or acids or alkali based extractions
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5. analysis
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immunoassays or GC-MS
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what are the advantages of hair analysis?
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what are the disadvantages of hair analysis?
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it has the widest surveillance window of any biological matrix (days to years) & segmental analysis can give longitudinal profile of drug use
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variation in growth rate can be problematic
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hair colour results in variation of the uptake of certain drugs into hair (based on binding preferences)
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allows flexibility in the timing of sampling because the average segment of 4cm of hair is approximately 3 months (based on average hair growth)
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environmental contamination can influence results (e.g. exhaled cannabis)
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washing the hair to remove external contamination is highly variable in its effectiveness
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opportunity to collect a second sample in disputed cases
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cosmetic treatment of hair can influence drug entrapment
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drugs are highly stable when incorporated into hair, therefore giving samples a long shelf life
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cannot identify alcohol abuse
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cannot provide a profile of drug use in the 6-7 days immediately after ingestion
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hair can be matched to individuals using appearance & microscopic examination
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it is more expensive then urine analysis
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it is not possible to adulterate or dilute the sample
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it is no more effective than urine at measuring cannabis consumption
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sampling is non-invasive
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there is a lack of international standardisation for both analytical & interpretation criteria (particularly in washing & extraction methodologies)
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higher capture rate of drugs than urine analysis
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using hair analysis is court is difficult because of lack of standardisation, lack of agreement on methodology, contamination, the effect of hair treatments, and differences between ethnic groups
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