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Expert Report Levels Explained

By Rebecca Hill, Senior Reporting Scientist


When an Expert Report is issued by Lextox, the results table shows the levels of drug and / or metabolite detected in the hair sample. What do these levels mean, how are they calculated and what are the limitations of the levels when carrying out a hair drug test?

What do the levels mean?

In order to help with the interpretation of the results, Lextox use the ranges low, medium and high. These levels provide an indication of the level of drug / metabolite detected in the hair sample provided for hair drug testing.

How are the levels calculated?

The levels are derived from a statistical analysis of other positive samples that have been analysed at the Lextox laboratory. A common misconception is that the test is a hair follicle drug test, sometimes referred to as a hair follicle screening. In reality, it is a hair strand test.

Results from positive samples are collated, ordered numerically and divided into three groups (ranges). The range of the lowest 25% of the data is used for the low range, the highest 25% of the data is used for the high range and the middle 50% of the data is used for the medium range.

The ranges applied are drug-specific and differ between drugs; therefore, the range for a drug should not be directly compared with a different drug. In addition, the range thresholds applied are specific to Lextox and as such, range thresholds can vary between different laboratories.

What are the limitations of the levels?

There are many factors that can influence the amount of drug / metabolite detected in hair, such as the purity of the drug consumed (illegal / street drugs are not controlled or governed by strict protocols in the same way pharmaceutical drugs are and there is no guarantee of the contents and / or the purity of the drug used) and individual variations to drug metabolism and drug incorporation rates into hair. Studies have shown that individuals receiving the same dose of a drug showed substantially variable drug concentrations in hair.

In addition, the use of chemical hair treatments such as dye can damage hair, having the potential effect of reducing the concentrations of drug / metabolite detected during the hair test process.

As such, the levels detected in the hair do not necessarily correspond to a high, medium or low use. However, the levels provided are useful as a guide to changes in use of a drug by an individual.

If you would like to find out more information on hair drug and alcohol testing, you can speak to one of our Experts who are happy to help. You can call us on 029 2048 4141 or email [email protected].

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Published 10/10/23 – All information correct at time of publication