CANSFORD LABS
on Jan 10, 2020
While hair testing for drugs and alcohol is becoming much more prevalent in legal and social work, some of the nuances and complexities of this type of analysis remain shrouded in misinformation. One of these areas is cut-offs.
The cut-off is the point of segregation between a negative and positive result. It provides an essential yardstick for results to be measured against - after all, you can’t have a positive and a negative without drawing a line between the two.
Cut-offs are used in all analysis methods, including, hair, blood and urine tests and their values vary between different substances (the value for cocaine is different to cannabis for example), types of sample (urine, blood, hair, saliva), and the test method in question. They exist to minimise false positive results (the detection of drugs resulting from external contamination or environmental contamination, including passive use), and to confirm true positive results.
Cause for concern exists because of a perceived uncertainty or grey area. Just because a test result is ‘negative’ (below the cut-off point), it doesn’t necessarily mean a person has not been drinking or using drugs. It tells us that this person is not a regular drug user, because the test has a result well above cut-off - but one-off drug use may not be detectable above the cut-off either.
- You may like: What do drug levels in the system mean in reality?
The cut-off is a constant, but the variables are many. So how do you quantify this type of reading? Here are five things every social worker should know about cut-offs in hair drug and alcohol testing.
1. Hair samples are heterogenous
Hair (in addition to other sample types) is heterogenous, which, put simply, means every sample is different. In terms of analysing samples for drug and alcohol usage, this heterogeneity creates a degree of variability between individuals. Two individuals who take the same amount of a substance at the same time and who are tested at the same time are unlikely to receive the same numerical result.
Even a hair sample from the same individual can throw up different results. When a drug test with hair is performed, the hair strands are destroyed, meaning even if we test even on the same day, the two locks of hair will have two different combinations of strands. The hair is not homogeneous. Cut-offs allow these numbers to be better quantified and yield greater confidence in positive results.
2. Cut-offs can differ from lab to lab
Depending on the types of equipment used and varying methods, each laboratory may use different cut-off points when looking for evidence of a substance. Before testing a sample, a laboratory should provide you with a cut-off list for the drugs in question and relevant information which should clarify whether or not the testing is suitable for your needs.
In the case of hair testing, these cut-offs can also be found in the SoHT (Society of Hair-Testing) guidelines.
Drug and alcohol testing laboratories are not regulated, so they don’t have to be accredited to analyse samples. This means it’s on you to use an accredited laboratory (by UKAS to ISO/IEC 17025), especially when it comes to legal cases involving areas such as child protection.
It’s important to note that some labs get the accreditation for one or two analytes, and others to many more - they are both accredited by UKAS to ISO/IEC 17025. This means that a lab may be accredited to test for cocaine but report results for cocaine, benzoylecgonine, cocaethylene, norcocaine. Another lab may be accredited to test for cocaine, benzoylecgonine, cocaethylene, norcocaine and report results to all analytes it tests.
Not only does accreditation prove competence and assure quality, but the experience of the testing laboratory will have a direct impact on cut-off levels and overall accuracy.
3. Interpreting the results may require some detective work
Background context is crucial in interpreting hair test results. A definitive answer may require little interpretation, but when the results lie in the grey area (below cut-off, but traces of substances or relevant metabolites are present), it is vital to view them within the broader scope of all the salient information.
If a test shows traces of a drug, a laboratory analysis alone can’t say why. Is the test subject currently a heavy drug user or a historical user who is now clean? Working this out may require some additional information, depending on how close to the cut-off the results lie. By providing relevant background information to the laboratory, caseworkers and legal professionals play an important role in piecing together an overall picture which can help to illuminate the test results.
Occasionally, the person in question has used drugs, but drugs are not detected in hair because the levels are too low. This may mean that individuals are not regular users, and it cannot be said for certain that these individuals have not used drugs at all in the period covered by the hair samples.
4. Hair testing provides a long-term view of drug use
Compared to other sample types, a drug test with hair offers the widest window of drug detection. This is hugely beneficial as it provides the ability to track a test subject’s history of drug use, which, dependent on the length of the hair, can potentially span a period of more than one year.
The average rate for hair growth is 1 cm a month, so cutting the sample into 1 cm pieces and testing each segment can provide a month-by-month history of substance use. Hair testing also has lower cut-offs than other sample types. Put these two points together and you see that hair testing can give an accurate picture of long-term substance use.
The long-term perspective can be particularly important in legal cases surrounding child protection and parental substance abuse. By charting drug or alcohol use over time, it’s easier to gain a clearer overall view and potentially determine a pattern and quantity of usage.
5. Every test has its own cut-off
Any type of sample used for testing has its own cut-off for each drug; whether testing urine, saliva, blood or hair, cut-offs are always used. Although these may seem to vary wildly between different sample types (the cut-off for cocaine in urine is 300ng/mL and in hair is 0.5ng/mL when analysed by LC-MS/MS), they reflect the fact that drugs enter and remain in different sample types in different ways.
The variation in cut-offs depends on the drugs deposited in the body. Fewer drugs and metabolites are incorporated in hair than are excreted via urine. All testing methods have a minimum level below which the detection of drugs is not possible, and the cut-offs for hair samples are usually around the limit of detection. In contrast, the cut-offs in urinalysis are set considerably higher than the limit of detection, which makes it more likely for a result to be ‘not detected’ even though the presence of a substance is apparent (although this isn’t all down to cut-off levels, of course - hair testing is vastly more sensitive than urine testing).
Conclusion
- We must take into account that every individual’s hair is different
- Using an accredited lab will ensure the right cut-offs are in place
- Background context is vital when analysing test results
- Lower cut-offs in hair testing help to establish longer-term substance use
- Cut-off levels vary depending on the testing method
Cut-offs play an essential role in all methods of drug and alcohol testing. Although they might seem to complicate the analysis of results, their purpose is actually the opposite: to elicit better clarity and fairness. Test results are highly accurate, but results that fall close to the cut-off line can cause uncertainty. These “grey area” results often simply need closer inspection and interpretation within the broader context of the case.
Without cut-offs, environmental contamination could potentially lead to false positive results, the consequences of which could be devastating. In terms of child protection, it could mean the difference between a child being placed in care or being allowed to stay with their family.
