Field Testing by Law Enforcement
Law enforcement officers routinely use presumptive field tests, such as the NIK, Marquis, or Scott reagent tests, to identify suspected controlled substances at the scene. These color-change tests are designed to provide a preliminary indication of the presence of certain drug categories but are not confirmatory. Field tests are used to establish probable cause for arrest and to support initial charging decisions. They are not designed to serve as the definitive identification of a controlled substance for trial purposes.
Consider this scenario: A roadside field test identifies the substance in your possession as cocaine. You are charged with felony drug possession. Six weeks later, the crime lab results come back negative. The substance was not cocaine. This discrepancy is more common than most people realize.
Limitations and False Positives
Presumptive field tests have documented limitations including cross-reactivity with legal substances. Common legal substances that may produce false positive results include certain over-the-counter medications, household cleaners, food products, and dietary supplements. Research has shown significant error rates with field testing kits, particularly in conditions of extreme temperature, humidity, or when the testing officer has insufficient training. The subjective nature of interpreting color changes introduces additional variability. Your legal team should obtain the manufacturer’s specifications for the specific test used and research documented false positive rates.
GBI Crime Lab Confirmatory Testing
The Georgia Bureau of Investigation Division of Forensic Sciences operates crime laboratories that perform confirmatory testing using methods such as gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and infrared spectroscopy. These methods identify substances with a high degree of specificity and quantify the amount of controlled substance present. GBI lab results carry substantially greater evidentiary weight than field tests and are the standard for trial. The strongest strategy is for your attorney to always demand that lab testing be conducted and should not allow a client to plead based solely on field test results.
Discrepancies Between Field and Lab Results
Discrepancies between field test results and GBI lab results occur in a meaningful percentage of cases. The field test may indicate the presence of a controlled substance while the lab report identifies a different substance, a legal substance, or no controlled substance at all. When a discrepancy exists, the lab result controls. Building a strong defense record means your attorney obtain the lab report as early as possible in the proceedings and compare it against the field test results documented in the arrest report. Any discrepancy provides grounds for dismissal or reduction of charges.
Delayed Lab Results and Plea Pressure
GBI crime lab backlogs can result in significant delays before confirmatory results are available. Prosecutors may pressure defendants to accept plea offers before lab results are returned, particularly when the defendant is in custody and bail is high. Your defense starts with advise clients against pleading guilty based solely on field test results and should advocate for bail reduction to avoid coerced pleas. If the lab result differs from the field test, a defendant who has already pled guilty faces the difficult process of withdrawing the plea.
Challenging the Chain of Custody
The chain of custody documents the handling of the substance from seizure through testing. Any gap in the chain, including periods where the substance was unsecured or where documentation is incomplete, may provide grounds to challenge the admissibility of the lab results. Your defense may involve obtain the complete chain of custody documentation and identify any irregularities. The Confrontation Clause also requires that the analyst who performed the testing be available for cross-examination, as established by Melendez-Diaz v. Massachusetts (2009).
Weight Discrepancies
Weight discrepancies between the field weight recorded at arrest and the lab weight may indicate loss of substance during transport, contamination, or errors in the original measurement. Weight is critical in Georgia drug cases because it determines whether the defendant faces simple possession, possession with intent to distribute, or trafficking charges with mandatory minimums. A weight difference that moves the quantity below a trafficking threshold can mean the difference between a mandatory minimum sentence and a probation-eligible offense. The key move for a qualified criminal defense attorney is to always compare field weight with lab weight and challenge any discrepancy.
Independent Testing
Defendants have the right to request independent testing of the substance by a private laboratory. O.C.G.A. Section 17-5-55 provides for the preservation of evidence for defense testing. Your attorney will typically file a timely motion to preserve the substance and to obtain a sufficient sample for independent testing. If the state has consumed the entire sample during its testing, leaving no material for defense testing, this may raise due process concerns under the principles established in California v. Trombetta (1984) and Arizona v. Youngblood (1988).