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New Guidelines

Cut offs, drug panels, screening and confirmations


A modern testing laboratory wants to provide a good service at a good price.

However, the lab can be constrained by the following:

Throughput – robot sample handling and chemical test methods need to suit the lab and the client. No client would wait 6 weeks to get the best analytical result.  Similarly, no client would pay £5000 per test, especially in the workplace sector where the vast majority of tests are of course negative.

The client enters into a Service Level Agreement with the laboratory. Almost always this means the lab tells the client which drugs at which levels can be screened and confirmed. Very few clients know their Mexedrone from their Mephedrone.

This drug list or “panel” is usually based on immunoassay tests which allow negative (drug free) samples to be quickly screened and reported.

Logically, the client expects the vast majority of his/her employees to be drug free, so receiving a quick report of “no drug use detected” makes perfectly reasonable business sense.

Bear in mind, this “non detected” applies ONLY to the drug panels that are observed in the screen. The donor could be overdosing on Cocaine and be deemed “negative for our panel” if Cocaine was not part of the panel.  This detail is key.

If this lab screens a sample as presumptive positive using their screening method, then a second portion of the sample will go forward for a confirmatory test.

This confirmation test is almost always mass spectrometry which offers both sensitivity (low reporting concentrations) and specificity (no ambiguity) for a report to the client.

Dependent on the sensitivity of the screening technique, ELISA, HEIA, EMIT a screening cut off will be determined.

Mass spectrometry will offer a lower confirmation cut off, and will be reported as the final result.

A sample which is lower than the screening concentration for a particular drug, will NOT go forward to mass spectrometry analysis.

In practice, that means a urine sample containing 280 ng/ml of diazepam, will be screened as negative, if the screen cut off is 300 ng/ml.

Even though the mass spectrometer used in the lab could accurately measure (and report) 20 ng/ml, the donor sample would never see the mass spectrometer, as it is screened negative at the initial test stage.


This is the way the larger test labs work.


Collection Services


Many employer clients do not fully appreciate the necessity of having samples collected and transported properly.

EWDTS recognise this, but the situation and possible resolution is quite complex.

ISO 17025 is the accreditation standard for test and calibration laboratories. UKAS in the UK have already accredited the collection services of one drug testing laboratory. This path is available to existing ISO 17025 Laboratories or test labs seeking this mark.

However, the vast majority of collection agencies are not in fact ISO 17025 Labs.

Also the vast majority of existing ISO 17025 Workplace Drug Testing labs have NOT sought accreditation for their collection services.

This is partly due to the fact that the collectors are not laboratory employees, and also the test labs may believe that most or many elements of ISO 17025 do NOT apply to collection services.

We therefore have an uncontrolled system, which when it goes wrong is spectacular.

Reference the oral fluid cocaine result from last year, which involved a bus driver.



The way forward


The way forward was considered by the EWDTS technical committee during 2014 and 2015.


  1. The European drug scene had dramatically changed in the preceding years.
  2. Many smaller labs screened with mass spectrometers and were not inhibited by high throughput chemistries.
  3. Due to improvements in instrumentations, lower limits of quantitation were easier to achieve and expanded drug panels which reflected the current drug scene were simpler to include in the Service Level Agreement.



Within the EWDTS there was a difference of opinion.


Larger, established testing laboratories wanted to maintain their core panel.

Their core panel was derived due to the availability of the test reagents which their robotic high throughput processes used. Almost all of these chemical tests were derived by US companies to allow laboratories in the US conduct their DOT Federal programmes.

If a new drug hit the scene and no test reagent was available, then mass spectrometry would be required to perform the initial screen. This is especially true if the new drug was European sourced, e.g. Phenazepam and Mephedrone.

That meant inefficiency and more cost, combined with the longer reporting cycle.

In the other corner were the smaller labs.

100% mass spectrometry for screening and confirmation.

Larger test panels, more agile to adjust to changing drug patterns.

By definition, less samples as they were smaller, but taking the attitude that sample growth would result in more equipment purchases due to the increased revenue.


New Guidelines


For Urine, Oral fluid and urine the new screening panels and subsequent confirmation panels are a step in the right direction. They are not the two or three steps necessary.

If mandated panels actually reflected what I would term “drug reality” then the large labs could not sustain their current business model.

In the UK Tramadol is an opioid like prescription drug which is very commonly used by the NHS. It is commonly abused but it is not a common drug on standard panels.

Ketamine is a similar story, with several deaths reported due to its abuse.

In Ireland, Gabapentin is a common street drug as is Pregabilin (Lyrica).

Employers should be encouraged to review their SLAs to ensure that the reporting panels reflect reality.

Almost all testing laboratories advise employer clients that their results should be shared with an MRO a medical review officer. This medical or toxicologist expert will review donor information and relate this with laboratory results.

I would strongly suggest that clients also employ the MRO to review the SLA to make sure it is current too.





Few people outside of the laboratory sector understand the mathematical uncertainty in the results that laboratories report.


These uncertainties is the term used to account for all the variables in the process of the analytical sampling and testing. All the small details added up to understand how wide a span of possible concentration ranges correct the result could be.


These expanded uncertainties of measurement can be quite large. 30 -40% is quite common. This means that the labs report a “greater than x” number where x is at the lower concentration range of the result. Each drug will have its own uncertainty range within the method used.

For example, an instrument may report a result of 5.0, if the uncertainty measurement is 40% then the actual concentration range of the possible result lies in the range 3.0 to 7.0  That is 5.0 +/- 40%. The laboratory will then report a result of “greater than 3”.   The smaller the uncertainty then the more precise and repeatable the lab processes are.

Again, this is a good indicator of lab performance and is something the client should ask at the SLA stage.

If the lower end of the uncertainty range fell below the confirmation cut off then the lab would correctly report the sample as negative.

This is important to remember.  Laboratories never report zero.


Not detected

Below limit of quantitation

Less than


Are typical terms used.






The future


The UK is expected to go the same way as Ireland. The new Psychoactive Substances Act will force the headshops to close. The trade will go underground, and be internet only.

New compounds will surface with little or no known therapeutic data.

People will ingest these new white powders and dose based on a friend’s advice.

AgriYork are collaborating with London hospitals in a study to sample from drug users presenting to emergency rooms.

These volunteers will agree to have blood and oral fluid samples analysed for new psychoactive substances. This it is hoped, will lead to dose concentrations and symptoms data. Bear in mind, these patients are ill, that is why they are at A&E.


New psychoactive will change the workplace drug scene too. The traditional heroin, cocaine use is reducing. Cannabis is becoming decriminalised in many places, and prescription benzodiazepines are increasing dramatically.

Last year in Norway, their customs reported that New Psychoactive Substances (NPS) accounted for more seizures than all of the traditional illicit drugs combined.

EWDTS and the testing laboratories will need to adapt to this.


What may happen?


Less testing but more comprehensive.

Why pay €30 to screen for 6 drug groups if two of the groups have no relevance?


Better to pay €60 and look for as much as possible.


In a “for cause” situation a more comprehensive test makes more sense. In an accident situation with all the other attendant costs related to production, medical treatment, litigation etc. I would not skimp on the lab work.



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