Cansford Labs guidelines for drug testing in the workplace – Part 2

Understanding cut-off

When testing drugs in urine, saliva or hair samples, results are evaluated against established “cut-offs” for each of these type of sample before the issue of certificate of analysis.

“Cut-off” is a value which the results obtained in the analysis are compared against. When results are below the cut-off, they are considered as “Not Detected “or” Negative “, and when  above they are considered” Detected “or” Positive “

This explains why a result may be reported as “Not detected” even though the individual has taken some drugs.

Cut-offs may vary between different analytes


The cut-off for cocaine in hair samples is 0.5 nanograms per milligram (ng/mg) of hair and the cut-off for the metabolite of THC (which is the main component of cannabis), the 11-Nor-D9-THC-9-Carboxylic Acid (THC COOH) is 0.002 ng/mg of hair.

This remarkable difference between the cut-off levels of cocaine and THC COOH in hair is due to the different rates of incorporation of these compounds into the hair sample.

Cut-offs may change according to type of sample analysed

Each drug or metabolite has its own cut-off according to the type of sample tested, i.e., whether urine, oral fluid or hair samples are used in the analysis. For example, the cut-off for cocaine in urine is 300 nanograms per millilitre (ng/mL) of urine and in hair is 0.5 ng/mg of hair, when analysed by LC-MS/MS.

The cut-off values of different types of sample, usually reflect the levels of drugs that are found in them. For example, levels of cocaine in a survey of over 7,000 hair samples were over a range from 0.2 to 159.9 ng/mg of hair in 99% of the samples [2]. In the same study, 99% of the levels found in the results of the metabolite of THC  the THC COOH, were in the range from 0.001 to 0.052 ng/mg of hair.

In the case of urine and  oral fluid, the levels of cut-offs are used:

a) to reduce the chance of reporting that drugs have been taken when the drugs were taken involuntarily (passively), as is the case with drugs that are smoked;

b) to eliminate the detection of drugs, when drugs were used at an earlier time (for example, eliminating the detection of drugs used over the weekend outside the workplace). This is very important in the workplace, where it is crucial to know whether an individual is under the influence of drugs or not, so as to minimise risk of injury to colleagues and the general public.

In practice, it means that results of urinalysis are reported as “Not detected” when levels are below the established cut-off even though the presence of drugs is clear.

A positive result of a urine or oral fluid analysis may be used to confirm if a person has used or was exposed to a drug. A negative result, however, does not refute use of or exposure to the drug

In contrast with the cut-offs employed in urinalysis, the cut-offs for hair samples are much lower and are usually at around the limit of the detection of the methods (all methods have a minimum level below which they cannot detect drugs). This is in contrast with the cut-offs employed in urinalysis, which are much higher than the limitation of the methods, which means that results of urinalysis are reported as “Not detected”even though the presence of drugs is clear.

Cut-offs vary depending of the method of analysis

Cut-offs vary according to the methodology used, thus, cut-offs for screening tests by immunoassays are usually different from those analysed by chromatographic methods. For example, according to SoHT guidelines for drug hair testing, when testing for cannabis use, the cut-off test for THC using an immunochemical is 0.1 ng/mg and for a chromatographic test the metabolite THC-COOH is 0.002 ng/mg of hair.

The cut-offs employed in hair analysis are usually analytical cut-offs established at the limit of quantification of the methods used

Cut-offs may vary between testing laboratories

Testing laboratories utilise different procedures in the analysis of the samples in conjunction with different equipment.

These and the experience of the testing laboratory will have an impact in the cut-offs levels and results.

It is therefore important that before performing the analysis, clients are informed of the uncertainty of the measurement at the cut-off levels.

Uncertainty of measurement at Cut-off

The total uncertainty of a result of a  hair test is derived mainly from the pre-analytical and analytical variations that contribute to the total uncertainty of drug detection in hair. The uncertainties of biological measurements should be considered when interpreting the resulting data.


Do you really need an accredited testing laboratory?

Drug/alcohol testing laboratories do not have to be accredited in order to analyse samples, i.e., it is not a regulated industry like some regulated industries e.g. financial institutions are regulated by the financial services authority.

By holding an accreditation, a laboratory provides evidence of competence to their customers.

Accreditation of laboratories testing drugs in hair samples adds value to the practice by improving compliance with standards and guidelines for the performance of laboratory analysis.

Different countries have different accreditation bodies and individual countries have their own accreditation body that follows international standards that usually certify laboratory competency such as ISO/IEC 17025. In the United Kingdom it is the United Kingdom Accreditation Services (UKAS); in the USA, the ANSI-ASQ National Accreditation Board (ANAB); in Germany, the Trägergemeinschaft für Akkreditierung German Association for Accreditation GmbH (TGA); in France, the Comité Français d’Accréditation (COFRAC); in Portugal, the Instituto Português de Acreditação (IPAC); in Chile, the Instituto Nacional de Normalización (INN); in Brazil, the Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (Inmetro), to cite a few examples.

Why ISO/IEC 17025?

ISO/IEC 17025 specifically addresses factors relevant to a laboratory’s ability to produce precise, accurate and reliable results.

To ensure continued compliance, accredited facilities are re-examined annually to ensure they maintain their standards of technical expertise.

Accreditation to ISO/IEC 17025 includes:

  • Ongoing technical competency of staff;
  • validity and appropriateness of the methods;
  • traceability of measurements and calibrations to national standards;
  • appropriate application of measurement uncertainty at cut-off levels; suitability, calibration and maintenance of test equipment;
  • the testing environment;
  • quality assurance of test, inspection or calibration data;
  • service to customer;
  • adherence to continuous internal audits.

What kind of accreditation?

Worldwide laboratories involved in drug testing are accredited by the ISO/IEC 17025 standards either using flexible scope or non-flexible scope.

Non-flexible scope, laboratories are accredited taking into account each substance. In this type of accreditation the laboratory cannot add any substance but the accrediting body, such as the United Kingdom Accreditation Services (UKAS) assesses the performance for each individual compound. It is therefore a very tight process.

Flexible scope the method utilised by the laboratory is accredited. In this type of accreditation the accredited laboratories can modify or add new compounds to the existing method, or even develop new methods involving the technology already in the lab scope, without the approval by the accrediting body is required, and claim that they are accredited. In some other countries accreditation is made with flexible scope, which requires them to take further certification specifically targeting the covered in drug testing, detailing what substances to be assessed.

In the UK, accreditation to ISO/IEC 17025 is with the rigid non-flexible scope. 

Testing Laboratories accredited to ISO/IEC 17025  in the UK are required to successfully participate in regular proficiency testing programs or inter laboratory comparisons as an on-going demonstration of their competence for the analytes they are accredited.

Successful participation in Proficiency Testing is what really matters to you!

Check if the laboratory you are using is accredited for all tests and drugs you need. In the UK, ISO/IEC 17025 accreditation is granted by UKAS (United Kingdom Accreditation Service). Each testing laboratory is issued with a testing laboratory number. For example, 7484 is Cansford Laboratories’ UKAS Testing Laboratory number.

Accreditation is test specific, in order for a test to be accredited, both the parent drug and metabolite should be detailed on the laboratory’s schedule of accreditation. For example, labs could state they are accredited for testing a hair sample for Cannabis, however, unless they are accredited for the parent drug (THC) together with a metabolite (e.g. THC-COOH), the Cannabis test as a whole is not accredited.

The details of each lab’s accreditation can be viewed on by clicking here then enter the company name and click on testing labs, this will show if a company is accredited, if they are it will state their schedule of accreditation.

Sample Collection


The degree of training varies tremendously from company to company yet it is this part of the drug & alcohol testing process that is most commonly the weakest link in the ‘chain of custody’ process and therefore the most liable to challenges if not performed correctly!

Not all sample collectors are the same! Rigorous training programme for sample collection is key for a successful laboratory result

When you are having someone come into your organisation to collect a hair sample it is very important that they know what they are doing and disrupt your normal activities as little as possible.

Drug testing companies usually have their own network of collectors, but how they manage that network varies from company to company. Here are some important points:

  • Obviously, a sample collection needs to be performed by a courteous collector who must be responsive to your client’s needs. It starts with being flexible to take the sample at a day and time that is convenient for you
  • All laboratory processes related to drug or DNA testing require the assurance that there is no margin for errors at the point of sample collection
  • The best quality of laboratory test result is only valid with the sample collected correctly and with chain of custody fully guaranteed
  • The validity & quality of the laboratory test result is directly related to the skill of the sample collection and the enforcement of the chain of custody procedures
  • When the laboratory performing the tests is accredited, it is natural that the accredited laboratory will want to ensure that the collectors are properly trained, as quality must be reflected in all activities

The best companies train their collectors not only on how to take a sample, but also how the analysis is performed, providing an  understanding of the importance of their role and how it affects the outcome of the testing

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