Use of Field Tests Comes into Question

Written by: Joe Mangiardi, NES, Inc.



Written by: NES, Inc. Staff

Misunderstood field test equipment can lead to undeserved arrests.

Misunderstood field test equipment can lead to undeserved arrests.


Field Test Results Questioned

Recent events involving presumptive field tests have led to questions being raised about their use. Several months ago a field test of an unknown white substance influenced an officer to interpret the results as positive for methamphetamine and, consequently, to arrest the driver. Subsequent lab tests revealed that the substance was sugar that had fallen off of a Krispy Kreme doughnut. In another incident, an officer noticed a sock filled with a crystalline substance on the vehicle dashboard. The driver claimed it was used to defog the windshield. A police officer tested the substance, interpreted the results as positive for methamphetamine, and arrested the driver. The unknown substance turned out to be Fresh Step Crystals, a silica-based cat litter.


Doughnuts and cat litter can be confused for meth by field tests

Left: doughnuts; Right: closeup of silica-based cat litter


In November journalists with ProPublica looked into the reliability and use of these presumptive field tests, which are used by almost every law enforcement agency. They found similar incidents occurring in one Florida sheriff’s office. According to the reporters, the sheriff’s office arrested 15 people on drug charges in the county on the basis of field tests wherein what was tested was later determined not to be a controlled substance by the Florida state crime lab.

A lieutenant with the Florida sheriff’s office decided to run an experiment with the field test they were using. The lieutenant tested a substance known not to be meth and arrived at the conclusion that the kits were giving a false positive result. The sheriff’s office ordered all officers to turn in their remaining test kits. Reportedly, prosecutors dropped charges against a number of people arrested for possessing meth. As it turned out, the lieutenant had misread the color change—the test results had actually been negative. Unfortunately, little could be done about the dismissed charges. State records show that in 2014 approximately 25% of substances described as meth by the Hillsborough sheriff’s office—determined via field testing or otherwise—were not shown to be positive when tested by the Florida crime lab. In 2015 this rate was approximately 21%.


Three Meth Examples

Pictured above are three examples of what meth can look like.


Lack of Training Blamed for Field Test Interpretation Errors

Training came into question. It turned out that the officers had received little or no formal training on the proper use and interpretation of field test equipment. And, while some agencies do provide training, there are no such requirements throughout the U.S. The Phoenix Police Department is one agency that limits who can use these field kits and requires officers to take a two-day course to get certified to do so. They are also required to take an annual refresher class and pass an exam to get recertified.

In a 2011 federal survey of 10 agencies that use field test kits, only two provided formal training to their officers. According to ProPublica, an analysis of arrests and criminal court data claims at least 100,000 convictions a year rely on these tests, most of which are pleaded out before trial. Training is not the only reason these field test kits provide a false positive or a false negative. The tests are only potential indicators. That’s the best the science behind these kits can do. Substances other than those the drug the test was designed for can also produce a color similar to what would be considered positive. The test kit that produced the characteristic orange color that indicated the doughnut sugar was meth is one such example. The sulfuric acid in the kit caramelizes the sugar and may produce the same color result as meth.


kits used for meth field tests

Left: meth test kit; Right: color tests


Training Does Not Prevent All Errors

In Las Vegas officers who are allowed to field test substances and who are trained to do so have still arrested people based on false positives. Officials with the Las Vegas crime lab have formally advocated abandoning the use of field tests for certain kinds of drugs, including meth. With the combination of the technical limitations of these kits and poor training—or the lack thereof—false results can be expected. ProPublica reported that in Houston more than 300 people were arrested based on incorrect field results.

The results from field tests continue to remain inadmissible at trial in nearly all jurisdictions in the U.S. Only results from lab tests are admissible. There are also conflicts between law enforcement and manufacturers who instruct their customers on proper use. As one example, the National Forensic Science Technology Center (NFSTC) does not advocate field testing of liquids, though some manufacturers of these kits provide instructions that support such testing.


two examples of Raman spectroscopy field test equipment

Pictured above are two examples of Raman spectroscopy field test equipment.


Technological Improvements Cannot Replace Lab Analyses

More and more agencies are using new instruments for testing narcotics that have appeared on the market in the past five-plus years. These new instruments may provide a more reliable method for identifying drugs but they, too, have limitations and do not replace laboratory analyses. As an example, users have been given false positives for fentanyl using one of these instruments when they tested methamphetamine that was not yet dry.

Training on the use of the field test kits and the new drug-detection instruments is essential. Training has to involve more than merely learning how to use the equipment. Some level of understanding about the relevant chemistry and how the instruments work is important and needs to be part of that training. A “black-box” approach, in which officers only learn to use the instruments, is insufficient. Users need to know more, such as what can produce false results, when and why the instruments shouldn’t be used, how to identify substances that can affect their use, and how to deal with exceptions.


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Propublica Article: Confusion Over Drug Tests Highlights Lack of Training for Florida Officers