Whether you are taking a drug test or administering a test to your employees, it is useful to know what the process of drug testing involves and how drug testing works.
Usually, urine and oral fluid drug tests are broken down into two stages:

  1. The initial screening stage – which yields a qualifiable result.
  2. The confirmation stage – which yields a quantifiable result.

If employees pass the initial screening, they do not progress to the second stage.

1. Initial Drug Screening

The screening stage can be done in one of two ways:

  • At Point of Care (POC) – which is an instant, onsite test.
  • Via a lab test (such as EMIT/ELISA/CEDIA). Screening is often done using immunoassay techniques.

POC drug testing is the most common type of workplace drug testing. Using simple testing kits with fast results times, the presence of drugs can be identified from a urine sample or saliva/oral fluid sample. Another POC type of testing is the use of breathalysers to identify alcohol use.
Lab testing is where a sample is tested at a laboratory by specialists. This method of drug testing takes longer to obtain results but offers a higher degree of accuracy.

2. Confirmation of Drug Test

In the case of a non-negative drug test, sending the sample to a lab for confirmation is a vital next step in drug testing. The confirmation stage can only be done at the Lab (via LCMS/GCMS etc…), and ensure that drug use is confirmed before actions are taken against individuals.

Can I just use the drug test screen result?

Some employers or organisations, in an attempt to cut costs, will only use drug test screen results. They do not send Non-Negative samples to the laboratory for confirmation analysis. This will not give them a fully legally defensible result and therefore is not recommended. Results can be successfully challenged, if a policy is not comprehensive enough or properly followed to provide legally defensible results.

The Cut-Off Level

One of the key concepts within drug testing is the application of a cut-off level. This is the point which segregates a test result as being either positive (+ve) or negative (-ve).
Drug Test Window of Detection Graph
For drug screening tests, a cut-off level is chosen that will optimise drug detection but minimise the number of “false positive” results. This is why the following must be considered:

  • Accuracy
  • Sensitivity
  • Specificity
  • Reproducibility (i.e. how consistently these figures are achieved time after time)

It should be noted that there are a large number of inferior tests currently available on the market. These may publish high accuracy figures but are unable to reproduce those claims across large scale manufacture.

How to interpret drug test results

It is important to note that a negative sample doesn’t mean that it is drug free. For example, it might contain a drug at a concentration that is lower than the defined cut-off.
If a drug test is reported as a screen positive (also known as a “non-negative” or “presumptive positive”), this merely shows a response. This is usually because a drug, or it’s metabolite, is present. It cannot show how much drug was taken, how potent the drug was or be correlated to any degree of impairment. As this is a screening tool, all screen positive drug tests require a confirmation test if they are to be legally defensible.
Any drug test screen result (QUALIFIABLE), whether from a Point of Care device or from a Laboratory is never 100% accurate. It can therefore only be reported as Negative or Non-Negative. There are no legally defensible QUANTIFIABLE (i.e. figures) results available at this stage. If a Negative result is obtained, then a “PASS” is usually reported (unless foul play/adulteration / dilution etc is suspected). Correct training for Collection Officers and the use of a Sample Validity Test such as urine adulteration test strips can assist with this.
All Non-Negative results require confirmation analysis, which can only be done at the Laboratory. The laboratory will then issue a QUANTIFIABLE result. E.g. 26 ng/ml.

Parent drug and metabolites

It is important to understand that during the both the screen and confirmation stage, the drug test is not just looking for actual drugs in the samples. They are often looking for drug metabolites. Once the body takes in a substance, the end product looks much different, once it passes through.
In simple terms, drugs go into the body in the “psychedelic” form and can come out as a metabolite and/or also as the “parent drug”. The detection of a metabolite indicates that the drug has actually been consumed by the person.
Chart illustrating the effect of marijuana on the body
For example, the psychoactive ingredient in cannabis/marijuana is THC (delta 9 tetrahydrocannabinol). This is oxidized by the body and comes out as many different metabolites. One of the most prevalent forms is Tetrahydrocannabinol-11-carboxylic acid (THC-COOH).
Cannabis passes from the lungs to the bloodstream, and while the drug is freely floating in the body in sufficient quantity, a “high” is felt. Cannabis is liposoluble, meaning it absorbs into fat cells. Fat cells store the drug indefinitely until the body burns the fat cells for energy. When the cell is burned, the drug is metabolized and released back into the bloodstream. This is why cannabis can sometimes be detected in urine for up to 30 days after chronic and frequent long term usage.

What cut-offs are used in drug testing?

Many Point of Care drug test devices/kits are made for the mass USA market and use higher cut-offs. They can also test for drugs that are less relevant to the UK. Using higher cut-offs may mean that you will not detect a larger quantity of positive samples at the lower end. This will make your testing program less effective.
Cut-offs are never normally set to 0ng/ml (zero) for workplace drug testing or general drug testing (not including forensic testing). This is to rule out external contamination such as passive smoking, exposure rather than actual consumption etc.
It is advisable to include a section on this within your Drug and Alcohol Policy.

European Drug Testing Standards

If testing in Europe, to European standards, then you should look for a “Point of Care” drug test device/kit that has test strip cut-offs aligned to the European Workplace Drug Testing Society (EWDTS) laboratory screening standards where possible. The ITS range of Point of Care urine drug testing devices/kits and oral fluid drug testing devices/kits are manufactured with that in mind and specifically for the UK and Ireland market.

European Drug Testing Standards for Cannabis

The EWDTS (European Workplace Drug Testing Society) guidelines’ cut-off for cannabis at the urine screen stage is 50 ng/ml (POC or via Lab screen). This is a composite of all cannabis metabolite concentrations. If the sample is below this level, then the test is complete and classed as a NEGATIVE and therefore a PASS result.
If the sample is over 50 ng/ml, then the sample is sent on to a laboratory for confirmation analysis. The cut-off for the confirmation stage is set lower at 15 ng/ml because the laboratory specifically looks for one of the many metabolites. This metabolite is Tetrahydrocannabinol-11-carboxylic acid (THC-COOH). It can also be referred to as 11-nor-9-Carboxy-THC, also known as 11-nor-9-carboxy-delta-9-tetrahydrocannabinol, 11-nor-9-carboxy-delta-9-THC, 11-COOH-THC, THC-COOH, and THC-11-oic acid.
Any result for Tetrahydrocannabinol-11-carboxylic acid (THC-COOH) <15ng/ml will be reported as NEGATIVE (PASS).
Any result for Tetrahydrocannabinol-11-carboxylic acid (THC-COOH) >15ng/ml will be reported as POSITIVE (FAIL) unless over-turned by a Medical Review Officer.

Legally defensible drug testing

At this point, you can then act upon this result (e.g. disciplinary) as it is now a legally defensible and qualifiable result unlike the screen qualifiable result of just “Non-Negative”.
It is always the confirmation (quantifiable) result that should be considered as the definitive “legally defensible” result. Therefore, any confirmed NEGATIVE / POSITIVE result that results in a PASS / FAIL can only be measured against the confirmation (quantifiable) cut-off levels.
The screen (qualifiable) results with the higher general cut-offs used, are only to be used as a guide/risk assessment to whether a sample requires further confirmation (quantifiable) analysis using the lower and more specific cut-offs.
In order to carry out legally defensible drug testing in your workplace, its important that you have a robust workplace drug policy in place. Not only will the outline your policy to employees, but will mean that in the case of drug testing and any positive test results, the consequences are clear and legally upheld.
If you need support to improve your workplace drug policy, or you don’t have one currently in place, you can learn more about our workplace drug and alcohol policy services here.

Drug Testing Kits from ITS

To carry out effective workplace drug and alcohol testing, it’s important you use quality products in order to obtain  reliable results. ITS are drug testing professionals, and our range of alcohol and drug testing kits and equipment are designed to be easy to use and highly accurate.
If you are unsure what drug testing kits to purchase, or are looking for advice on your workplace drug testing policy, don’t hesitate to get in touch with the ITS team.