Common misunderstandings in drug and alcohol testing in safeguarding cases

That matters in any legal setting, but especially in cases involving children. Local authorities, solicitors and the courts may rely on toxicology evidence when considering risk, parenting capacity, compliance with plans, or the reliability of what has been reported. If the testing route is not well matched to the issue in the case, or if the findings are taken further than the science allows, there is a risk of misunderstanding the evidence rather than being assisted by it.

Much of the confusion comes from the way testing is discussed more broadly. It is common to hear broad statements such as “the laboratory result proves use” or “the result shows abstinence”. These kinds of phrases may sound clear, but they can flatten important distinctions. A hair test result does not answer the same question as a urine result. A historical alcohol marker does not show intoxication at a specific point in time. A positive finding does not automatically explain how often a substance has been used, or what was happening in the wider circumstances of the case.

For professionals working in child safeguarding matters, it helps to move away from the idea that there is a single “drug test” or “alcohol test”. There are a number of different approaches, each with its own strengths and limitations. The value of any result depends on asking the right question in the first place.

Why misunderstanding happens

Part of the problem is that forensic testing is often confused with screening. In everyday conversation the terms are sometimes used interchangeably, but they are not the same. An initial screening process may indicate that a substance could be present (known as “presumptive positive”). Forensic laboratory analysis is a separate step, carried out using validated methods and stricter controls. In legal and safeguarding settings, that distinction matters.

Another difficulty is that people understandably want certainty from the science. In family proceedings, uncertainty can be uncomfortable. Professionals want to know whether a parent has used drugs, whether alcohol consumption is ongoing, whether a claimed period of abstinence is supported, and what weight should be attached to the findings. Testing can assist with these questions, but it does not always produce a simple answer. It is often more useful as part of the overall picture than as a complete answer in itself.

There is also a tendency with laboratory analysis to assume that timing can be established more precisely than it can. This is one of the most common misunderstandings in practice. Many people believe that laboratory analysis can show exactly when a substance was taken. In most cases, it cannot. What testing usually provides is a pattern rather than a timestamp.

Different tests answer different questions

The starting point is to understand what each sample type is designed to show.

Urine and saliva testing is generally used to identify relatively recent drug use and is generally carried out in-site. It can be helpful in the right circumstances, but it does not provide a long historical picture, and it cannot be used as evidence without laboratory confirmation. Detection periods vary depending on the substance, the pattern of use, the individual concerned, and the analytical method used. A result may remain positive after the immediate effects of a drug have worn off, which means it should not be treated as a direct measure of impairment at the time the sample was taken.

Blood testing can also assist where the issue is recent use, although the window is often narrower. In alcohol cases, blood may be used in different ways depending on the marker being tested. Direct alcohol itself is short-lived. Other markers can provide a broader picture, but they still need careful interpretation.

Hair testing is different. It is used because it can provide a retrospective view over a longer period. Segmental analysis may allow a broad month-by-month interpretation over the relevant length of sample, which can be useful where the concern is a pattern of use over time. That does not mean hair can show the exact date of use. It cannot. Its value lies in helping to build an overview rather than pinpointing a precise event.

Nail testing may also be used where a longer historical view is required. Like hair, it is not a measure of current impairment or a precise chronology. It is another tool that may assist when matched to the right evidential question. Nail samples cannot, however, be segmented.

For alcohol, PEth testing has become increasingly important. PEth is a direct biomarker formed only when alcohol (ethanol) is consumed, which makes it a useful indicator of alcohol consumption over a period of up to four weeks. This can make it particularly relevant where the issue is not simply whether alcohol has been consumed at all, but whether there is evidence of ongoing drinking within a recent period that matters to the case.

A positive result does not explain itself

One of the more persistent myths is that a “positive” result tells the whole story. It does not. Terms such as “positive” and “negative” are not always helpful when trying to establish nuanced changes under the burden of proof of Balance of Probabilities.

A positive result may show that a substance, metabolite or biomarker has been detected in the sample analysed. That is important, but it is not the end of the exercise. It does not automatically tell the reader how often the person used, whether the pattern was sustained, whether there are alternative explanations that should be considered, or what significance should be attached to the concentration found.

That is one reason expert interpretation remains so important. Scientific findings need to be understood alongside the history of the case and the background of the client, the type of sample taken, relevant disclosure, and any surrounding information about medication, medical treatment, environmental factors, cosmetic treatment in hair cases, or other matters that may affect interpretation.

This is not to downplay the value of the result. Toxicology evidence can be highly useful. The point is that it should not be read as though it were a stand-alone narrative. A result is part of the evidential picture, not a substitute for the picture as a whole.

Historical use is not the same as impairment

Another area where confusion arises is the relationship between detection and behaviour.

Hair and nail testing can assist with historical patterns of use, but they do not show whether a person was intoxicated, impaired or unable to care safely for a child at a particular moment. That kind of conclusion cannot be drawn from a historical matrix alone. In the same way, the presence of an alcohol biomarker over a certain period does not, by itself, establish what the individual’s presentation was on a specific day.

This distinction is important in safeguarding work because professionals are often trying to assess risk in practical terms. A local authority may need to know whether concerns about a parent’s presentation are supported by toxicology evidence, whether abstinence has been maintained, or whether the account being given is consistent with the scientific findings. Testing can inform these questions, but it must be kept within its proper limits.

There is a difference between evidence of use and evidence of functional impact. In some cases the two may sit alongside one another, but they are not interchangeable.

Detection windows are not fixed rules

Detection windows are often spoken about as though they are rigid and universal. They are not. They are guides.

A number of factors can affect how long a substance or marker remains detectable. These include the substance itself, dose, frequency of use, metabolism, health factors, the sample type, sample matrix and the analytical method. That is why it is risky to rely on broad assumptions such as “this drug is always detectable for a certain number of days” or “a negative result proves there has been no use at all”. Hair treatments can also influence detection windows and the levels of drugs present.

In practice, detection windows should be understood as part of a scientific framework, not as hard rules divorced from context.

This can be particularly important where professionals are trying to interpret a result against the account being given by a parent or carer. A result may be consistent with that account, inconsistent with it, or difficult to reconcile without further information. That assessment should be made carefully. It is rarely helped by overconfident language.

Choosing the right testing method

The most useful testing usually starts with a clear understanding of what needs to be established.

If the issue is very recent use, such as likely impairment at the time of a visit, a historical matrix may not be the best first option. If the concern is a pattern of alcohol consumption over recent weeks, a short-lived marker may not be enough. If the case turns on whether substance use has continued over several months, a narrow snapshot may not answer the question the court is really asking.

This is why the letter of instruction matters. Before any sample is taken, it is worth being clear about the purpose of the testing. Is the concern about recent relapse, ongoing use over time, frequency of use, or the credibility of what has been reported? Is there a specific allegation, or is the concern broader than that? Is the issue drugs, alcohol, or both?

These points are sometimes treated as procedural detail, but they go directly to the usefulness of the evidence. A poorly framed instruction can produce a result that is technically correct yet of limited practical value. A well-framed instruction is much more likely to produce something the court can actually use.

Why interpretation matters in safeguarding work

Safeguarding cases rarely turn on toxicology evidence alone. Social work evidence, chronology, police disclosure, medical information and the lived reality of the family all have their place. Drug and alcohol testing should be understood within that wider setting.

That is also why reports need to be written clearly. The intended audience is not only scientists. Reports may be read by lawyers, social workers, guardians and judges, all of whom need to understand what the findings mean, what they do not mean, and where caution is required. Clear language is also very important as in most cases, the client needs to understand what is happening.

Overstated reporting can be as unhelpful as vague reporting. If a result is presented more strongly than the science allows, it may distort the way the evidence is received. If it is too thinly explained, it may not assist at all. Good reporting sits in the middle. It is accurate, measured and clear about limits.

In public law proceedings, where the stakes are high and timescales are often tight, that kind of clarity is especially valuable.

Why misconceptions can create practical problems

Misunderstandings about testing are not simply academic. They can create practical difficulties in real cases.

A narrow instruction or window of detection may miss the real issue. A result may be taken further than it should be. Parties may assume that a negative finding closes the matter when it does not. Equally, a positive finding may be treated as though it answers questions about severity, timing or behaviour that the test was never designed to answer.

This can lead to delay, further applications, unnecessary dispute, or avoidable cost. It can also make case management harder, because professionals may find themselves revisiting issues that could have been addressed more clearly at the outset.

A better approach is not to expect certainty where the science does not offer it. It is to use the science properly. That means selecting the right method, preserving chain of custody, ensuring laboratory analysis is carried out to the appropriate standard, and reading the findings with the benefit of proper interpretation.

The role of Certis BioLabs

At Certis BioLabs, our role is to help professionals approach testing in a way that is proportionate, clear and suitable for the circumstances of the case. We work with UKAS-accredited laboratory partners and support drug and alcohol testing with careful reporting and professional interpretation.

That includes helping instructing parties understand which testing route is likely to be most appropriate, what the likely scope of the result will be, and what care should be taken in reading the findings. In safeguarding and family law matters, that kind of support can make the difference between evidence that is merely produced and evidence that is genuinely useful.

The aim is not to overcomplicate the science. It is to avoid oversimplifying it.

Conclusion

Drug and alcohol testing remains an important part of the evidential landscape in safeguarding cases, but it works best when its limits are properly understood.

There is no single testing method that answers every question. A result does not interpret itself. Historical use is not the same as impairment. Detection windows are not fixed rules. A positive finding may be important, but it still needs context.

For local authorities and legal professionals, the key is to be clear about what needs to be established and to ensure the chosen testing method is capable of addressing that issue. Where that happens, toxicology evidence can make a valuable contribution to fair and informed decision-making. Where it does not, there is a risk of asking more of the science than it can properly give.

Testing is at its most useful when it is treated neither as a blunt instrument nor as a source of certainty, but as one part of a carefully interpreted evidential picture.

Certis Bio-Labs Limited can be contacted via 01235 633 040 or at This email address is being protected from spambots. You need JavaScript enabled to view it..

References

Forensic Science Regulator and Home Office (2025) Forensic science activities: statutory code of practice – version 2. Available at: https://www.gov.uk/government/publications/forensic-science-activities-statutory-code-of-practice-version-2 (Accessed: 14 April 2026).

Hubbard, J.A. and Caban, M. (2025) ‘Review on toxicology testing in hair’, Journal of Applied Laboratory Medicine, 10(4). Available at: https://academic.oup.com/jalm/article/10/4/983/8099411 (Accessed: 14 April 2026).

Snozek, C.L.H., Krasowski, M.D., Colby, J.M., Johnson-Davis, K.L., Bruccoleri, R.E. and Melanson, S.E.F. (2026) ‘ADLM guidance document on laboratory testing for drugs of misuse to support the emergency department’, Journal of Applied Laboratory Medicine, 11(1), pp. 155–180. Available at: https://academic.oup.com/jalm/article/11/1/155/8414133 (Accessed: 14 April 2026).

Society of Hair Testing (2022) General consensus for hair testing. Available at: https://www.soht.org/images/pdf/General_Consensus_Hair_Testing_2022.pdf (Accessed: 14 April 2026).

Tavaglione, F., De Vincentis, S., Vassallo, G.A., Jamialahmadi, T., Fracanzani, A.L., Fargion, S., Aghemo, A., Miele, L., Abenavoli, L. and Mantovani, A. (2025) ‘Clinical utility of phosphatidylethanol to monitor recent alcohol use and abstinence: an updated review’, Clinical Biochemistry, 141. Available at: https://www.sciencedirect.com/science/article/abs/pii/S016882782502269X (Accessed: 14 April 2026).