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Testing meth labs – presumptive vs laboratory analysis

Written by Naomi Hosted & Rory Gardner
Forensic & Industrial Science

When you test a property for methamphetamine contamination there are two broad methods of testing commonly used; onsite presumptive screening and full laboratory analysis.

A presumptive test is a quick, on the spot test that will either show that a sample is not a certain substance or that it might be the substance in question. Common presumptive tests for methamphetamine include immunoassay and colorimetric methods.

Presumptive immunoassay tests are similar to a pregnancy test; enzymes in the kit react with methamphetamine and the result is shown as one or two lines appearing on a strip.

Colorimetric tests use colour changes to indicate the possible presence or absence of methamphetamine; common kits include specialised paper that is sprayed with a reagent causing an indicative colour change.

Laboratory analysis requires samples to be sent off-site and uses analytical methods (commonly chromatography coupled with mass spectrometry) to confirm the presence of methamphetamine in a sample. Laboratory analysis is also used to measure the concentration of methamphetamine in the sample.

Below we have laid out the pros and cons of each method to help you determine which testing is appropriate in different scenarios.

Presumptive testing

Presumptive test kit. This image is provided courtesy of Forensic and Industrial Sciences Ltd and must not be reproduced without their permission

Presumptive test kit. This image is provided courtesy of Forensic and Industrial Sciences Ltd and must not be reproduced without their permission

Presumptive testing methods are often used because they are cheap, quick and portable, meaning they can be used on-site to deliver instant results. But there are a number of factors that need to be considered when using presumptive testing.

The mechanisms of both immunoassay and colorimetric presumptive tests mean the results can often be difficult to read (lines or colour changes may be faint or only slight). This can lead to misinterpreted results.

These methods are based on chemical reactions, and other chemicals unrelated to methamphetamine manufacture can trigger the reaction that drives the colour change. This is known as a false positive.  False negatives can also occur if the sensitivity of the method is insufficient to detect the concentration present on a surface or the method is used inaccurately.

In 2010 Australian Customs arrested a woman at Melbourne Airport after a presumptive test gave a positive result for methamphetamine when used on 2.4kg of powder in her luggage.  Subsequent laboratory analysis by Australian Federal Police showed that the powder was actually lemon flavoured iced tea and the presumptive test had given a false positive result. The woman was released and Customs was ordered to pay A$5,000 damages.

While presumptive tests may be a good indicator, examples like this show that their results should be used with caution.

Presumptive tests give a positive or negative result and cannot be used to assess how much methamphetamine is present on a surface. This can be problematic for restorers and testing agents who need to know levels present in order to make a cost effective Remediation Action Plan (RAP). For example; it is generally possible to clean contaminated plasterboard containing less than around 2µg/100cm2 of methamphetamine but at higher levels cleaning is not an effective method of remediation.

So when do presumptive tests come in handy? They can be used as a tool for investigative purposes (i.e. precautionary testing), but they should not be used as verification for sign offs or for preparing a RAPs.

You should also keep in mind the word ‘presumptive’ when using these testing. A positive presumptive result means you presume it is the substance in question.

Laboratory analysis

This image is provided courtesy of Forensic and Industrial Sciences Ltd and must not be reproduced without their permission.

Analysing methamphetamine levels using gas chromatography. This image is provided courtesy of Forensic and Industrial Sciences Ltd and must not be reproduced without their permission.

In contrast to presumptive tests which can be used to get an indication of the presence or absence of methamphetamine, confirmatory laboratory methods such as gas or liquid chromatography are appropriate for the detailed assessment of a site, preparation of RAPs, test patches (to assess effectiveness of cleaning techniques) and for verification/sign-off purposes.

While laboratory testing is generally more expensive and takes longer to obtain results (sometimes several days), the possibility of false positives and negatives are eliminated, and objective results that cannot be misinterpreted are given. Unlike presumptive tests which only provide an indication of the presence or absence of methamphetamine, laboratory analysis will also provide measurements of the amount of contamination present on each surface tested. This information  can be used to create a detailed site assessment and RAP or can be used for the purposes of signing-off.

Presumptive Testing

Laboratory Analysis

“probably is methamphetamine”

“definitely is methamphetamine”

cheaper than confirmatory

more expensive than presumptive

portable, process samples on site

send samples to a laboratory

subjective interpretation

not subjective

false positives & cross reactivity

no false positives or cross reactivity

preliminary investigations & test patches only

detailed site assessments, test patches RAPs & verification

positive/negative result only

measures amount present precisely

positive result can actually be lower than amount stated for that product.


So which test should I use?

All potentially contaminated sites have to be assessed on a case-by-case basis to determine whether a presumptive test or laboratory analysis is more appropriate.

Before you start a job you should always remind yourself about the purpose of the test. Do you need to know the exact level (measurement of contamination) or are you looking for an indication of the presence or absence of methamphetamine?

If you decide that a presumptive test is more appropriate for the situation make sure to check the product data for cross reactivity and sensitivity information as well as the expiry date of the product.

If making remediation recommendations or signing off decontamination of a site then laboratory testing must be used, especially as the results may directly affect the health of future occupants. While the price of laboratory testing may be higher the results enable more effective and efficient remediation to be made.

What are your thoughts on presumptive and confirmatory testing methods for meth lab cleanup jobs? How do you determine which method to use? Comment in the thread below to share your opinion.

Want to learn how to collect samples for laboratory analysis? Attend the Jena Dyco Meth Lab Cleanup & Testing Course.

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