The main benefit of the use of hair samples in drug testing is specifically the longer window of detection it allows.
The results of hair drug analysis vary over a very wide range between individuals.
This wide variation is the result of many factors that influence the amount of drug incorporated into hair such as purity and frequency of drug consumed as well as colour of hair. Individual variations in drug metabolism and the effect of cosmetic hair treatment are also important.
It is not possible therefore to exactly correlate the levels detected in hair with the amount of drug ingested. One may assume that high levels detected in a hair sample may reflect higher use, however, this assumption can be misleading
The levels of drugs detected in hair are currently best used as a guide to changes of use in the individual when sectional analysis is performed or two different periods are compared in the same individual. This attribute can be used to monitor drug use patterns, demonstrating increasing or decreasing doses being used by the same individual over longer time periods.
On the other hand, the results can be compared with the results previously analysed by the laboratory. This means the results of one sample from one person can be compared with an average of the results detected in hair samples from a group of people that used the same drug. This approach is very useful when interpreting hair analysis results to draw conclusions about how much drug was used compared with other people (though not the absolute amount).
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