We are often asked if drug test kits are accurate; for which the answer is “Yes”; however requires further explanation.
The fact is that drug test kit accuracy is a more complex question than it appears. Yes, most drug test kits are accurate subject to their limitations in field testing.
Interestingly, initial screening in a laboratory uses similar technology to that in the test kit. The laboratory confirmatory test is however completely different.
Confirmatory testing in a laboratory uses state of the art analysers (normally liquid chromatography and gas chromatography and is entirely different to a single use disposable device used in field testing). The laboratory confirmatory test can identify not just the presence of drugs, but also the concentration of the drugs and the specific drug identified within the class of drugs being tested.
An on-site drug test kit is accurate but it is designed to provide a yes or no answer to the question. Is a drug class (different to a drug) most likely present in a concentration above a level that the test kit is designed for.
Therefore, a drug test kit is really designed as a risk analysis tool. It determines if a sample should be sent to the laboratory for further analysis. It can’t tell you if the sample contains a legal version of a drug in the same class as an illegal drug.
For example, Codeine use is legal in Australia with a prescription. Codeine belongs to the opiate class of drugs and Heroin belongs to the same class of drugs (Heroin is an opiate). A field device will identify the presence of opiates in the sample of someone who has taken a medication containing codeine. A further sample will need to be sent to the lab to confirm the exact identify of the drug in the sample (to rule out heroin) and at what concentration.
An important consideration is the fact that a sample will not reach confirmation testing unless it has been firstly screened, so the screening test whether in the laboratory or performed with an on-site test kit needs to be relatively accurate. Samples that are negative with on-site screening are not sent to the laboratory for confirmatory testing.
High quality drug test kits tend to have been validated by an independent laboratory to operate within certain criteria. This is the case in Australia and kit suppliers should be able to provide independent validation reports on request (especially when claiming to be compliant with a particular Standard).
Accuracy also tends to be something that is measurable and should be available from the kit supplier. As the levels of a particular drug in the sample increases or reduces away from the cut-off level the accuracy tends to increase. In general most test kits tend to have an accuracy of greater than 90% or better when the levels are greater than 50% away from the cut-off level.
Now this might sound like quite a variance but it is important to remember that we are dealing with extremely low concentrations of drugs/ metabolites. This us usually measured in the parts per million.
So in conclusion; yes drug test kits do tend to be accurate. However, the accuracy is subject to the quality of the test kit used, limitations like cross-reacting substances as well as the conditions that the kits have been stored in. All samples that aren't negative need to be referred to a laboratory. Only an accredited laboratory can refer to a sample as being "positive".
Choosing the right drug test kit is much more difficult than sorting apples from oranges. Drug test kits use different matrices (oral fluid or urine), target different drug classes at different cut-off levels and are very different in various countries.
This helpful guide will assist you in working out roughly which type of kit you should consider.
