Why use segmentation

Test case 1 - If a donor has stated they have stopped using drugs prior to the testing period their can still be carry over into the testing period, drugs carry over and small usage are hard to differentiate between.

It is therefore possible to get a positive result on a standard 3 month test if there has been significant drug usage prior to the testing period and abstinence has been adhered to during the testing period.

If in this case we segmented the hair sample into 3 x 1 month periods we could show for example the dissipation through the testing period and highlight no usage most recently, thus confirming the donors statement.


Case study

Cocaine banner.jpg

Instruction issued to provide an overview for the last 3 months to establish if the client was using Cocaine.

An alternative laboratory

A hair sample was collected at the end of May and sent to the laboratory, which carried out a hair strand test for cocaine to cover a 3 month history.

Hair sample cut to a single section of 3cm in length (non-segmented).

Result – Cocaine and cocaine metabolites were found above the cut-off.

Interpretation - Positive

The laboratory concluded:

“The levels observed in the 0-90 day segment indicated that the donor consumed cocaine on multiple occasions within the time period tested.”

All parties and the court therefore understandably assumed that the client had been using cocaine during the three month period March to May. This result was to be the determining factor in the decision making process with regards to the child’s residence.

Forensic Testing Service

Key Facts - The client interview established the following:

  • The client had previously used cocaine but claimed to have stopped using just over 3 months ago
  • There had been no hair cosmetics or scalp medications used that could influence drug levels in the hair

The matched hair sample and also a urine sample were tested by FTS to establish a 3 months history. The hair sample was cut to 4cm and segmented into 4 x 1cm sections and a urine sample was also collected and tested.

Result – Cocaine and 3 cocaine metabolites were found at very high levels in the oldest section and the levels reduced significantly in each section and only very low levels were found in the most recent section with only one metabolite present significantly below the cut-off, urine negative for cocaine.

FTS concluded:

“These results are compatible with the client using cocaine on a frequent basis up to around February. Cocaine use appears to have stopped sometime in February or possibly early to mid-March and there does not appear to have been any active cocaine use for the subsequent period of approximately 3 months up to the point of sample collection in May. These results appear to be consistent with the client’s declaration.”

These two conclusions are completely different, probably resulting in different decisions for this case.

This case also demonstrates the importance of an expert advising on the appropriate test profile for each case since an average of drug levels in a long hair section without the knowledge of levels in the hair section prior to the period of interest can produce a very misleading conclusion.

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