Hair specimen is necessary to complement blood and/or urine analyses as it permits differentiation of a single exposure from chronic use of a drug by segmentation of the hair for a stated growth period. Moreover, due to a frequent long delay between event and police declaration, hair can be the only solution for lack of corroborative evidence of a committed crime. Excepting the lower amount of biological material in children versus adults, there is no specific analytical problem when processing samples from children. The issue is the interpretation of the findings, with respect to the different pharmacological parameters. In some very young children, the interpretation can be complicated by potential in-utero exposure.

Two examples from daily practice are used to document these difficulties. Case 1: a 9 months old boy was found dead in his bed (sudden child death). Both parents were cannabis regular smokers. The investigators wanted know if the child had been exposed to drugs. A strand of hair that was 4,5cm in length and brown in colour was collected. Case 2: a mother under treatment was suspected of administering methadone to an 11 months old child. A strand of hair that was 6cm in length and blonde in colour was collected. Drugs were tested by GC/MS (THC, cannabinol, cannabidiol) and LC/MS/MS (methadone, EDDP) after decontamination by dichloromethane (2×5ml), segmentation, and liquid-liquid specific extraction.

In both cases, the mother admitted having used drugs during pregnancy.

THC tested positive in the hair of the child in case 1 at 0.42, 0.51 and 0.86ng/mg in the 0–1.5, 1.5–3 and 3–4,5cm segment, respectively. Cannabinol and cannabidiol were always identified. Methadone tested positive in the hair of the child in case 2 at 0.42, 0.46, 0.59 and 1.58ng/mg in the 0–1.5, 1.5–3, 3–4.5 and 4.5–6cm segment, respectively. EDDP only tested positive in the 2 last segments. Obviously, the concentrations measured in the hair are much lower than those observed in subjects using these drugs. In that sense, the frequency of exposures appears as un-frequent (low level of exposure), with marked decrease in the more recent period. However, the parents denied any administration in both cases. A least, four possible interpretations of the measured drug concentrations can be addressed: 1. decrease in administration in the more recent period; 2. increase of body weight due to growing, so the same dosage will result in lower concentrations in hair; 3. sweat contamination from the parents/mother at the time the child is with them in bed, the older hair being longer in contact with the bedding; and 4. contribution (from 1 to 100%) of in-utero exposure during pregnancy.

Very few papers have been published about the disappearance of drug after discontinuation of use or exposure (in case of in-utero exposure). In adults, it can take 6 to 9 months to have a negative hair result after ethanol, heroin or cocaine abstinence. The time course after delivery of disappearance of a drug incorporated during pregnancy has never been reported.

In these cases, it was impossible to conclude that both children were deliberately administered drug. The results of the analysis of hair could indicate that they were in an environment where drug was being used and where the drug was not being handled and stored with appropriate care. Contribution of in-utero exposure should be reviewed when the case involves a child under 1 year. In view of these results we concluded that a single determination should not be used firmly to discriminate long-term exposure to a drug.