Impaired driving is not limited to alcohol. Drug-impaired driving is more common now than ever before. From September 2019 to July 2021, NHTSA studied 4,243 drivers involved in crashes brought to level one trauma centers in seven locations across the United States. The study found that 54 percent of drivers tested positive for alcohol and a combination of alcohol and drugs. Of the total population studied, 22 percent were positive for alcohol, 25 percent were positive for marijuana, and 19.9 percent were positive for two or more drug categories. Although impaired driving is on the rise, drug-impaired driving continues to be underreported due to limitations in resources for forensic toxicology laboratories. When you’ve seen one forensic toxicology laboratory, you’ve seen one forensic toxicology laboratory. Funding streams, overarching agencies, policies, and state statutes determine how a forensic toxicology laboratory will provide testing in their jurisdiction for impaired-driving investigations. Most laboratories do not perform the same testing, and some differ within the same state.
In recognition of this significant discrepancy, NHTSA cooperated with the Society of Forensic Toxicologists to create a program to align the forensic toxicology laboratories nationwide. The Regional Toxicology Liaisons (RTLs) currently serve 14 states and the Pacific Territories. The purpose of the RTL program is to provide resources and guidance to public forensic toxicology laboratories and their highway safety partners to create collaboration and cohesiveness across and within each state. Since 2021, RTLs have been working with laboratories to streamline their testing and provide guidance for more funding opportunities for instruments, personnel, and training. Due to the program’s success, in October 2024, RTLs expanded to more states in the country. With over 150 publicly funded forensic toxicology laboratories nationwide, implementing the alignment strategy will take some time. While it has been a slow process, the work of the RTLs has brought more funding, training, and collaboration to forensic toxicology laboratories that otherwise would never have existed.
Forensic Toxicology Testing
A common question asked of forensic toxicology laboratories is, “Why does it take so long to get results from your testing?” As was mentioned, forensic toxicology testing is complex and can differ between laboratories. Most forensic toxicology laboratories are accredited by the American National Standards Institute—National Accreditation Board (ANSI/ANAB) using ISO/IEC 17025 requirements, which also may include the American Board of Forensic Toxicology’s checklist. Accreditation is essential for any forensic laboratory as it demonstrates their need to conform to specific requirements and shows an external entity oversees their work. When accredited, a laboratory also must comply with in-person inspections from external experts, off-cycle internal audits, and participate in proficiency testing (PT) programs. These steps ensure the laboratory operates within a known, approved framework and provides validity and integrity to the testing.
PT is a way for laboratories to establish accuracy in their testing and is typically included in the laboratory’s quality assurance (QA) plan. PT samples are provided by an external entity in various matrices, such as blood and urine. The PT contains known amounts of the drug of interest, but the concentration is unknown to the laboratory. Many laboratories require analysts to test PT samples yearly to demonstrate proficiency in any testing assay. Proficiency testing is used as a tool for laboratory improvement. If a laboratory has an unsuccessful event, an investigation occurs to determine the root cause of the discrepancy.
Laboratories are encouraged to implement the standards set forth by the ANSI American Academy of Forensic Sciences Academy Standards Board (ASB). Each forensic science discipline is represented by its corresponding Consensus Body, which creates the standards specific to each area of science. The ASB documents are crucial to creating harmonious testing and practices across all forensic toxicology laboratories.
Accreditation requires laboratories to provide testing in several separate and distinct steps while adhering to a QA plan. While this provides transparency and integrity to the testing, it also adds time to process samples, such as blood and urine. A large part of why testing takes the time it does is due to the laboratory’s QA system and the layers of review required to meet accreditation standards. For example, when testing BACs in blood or urine, the laboratory must prepare the sample before placing it on the instrument and ensure the instrument is appropriately calibrated for the test to occur. The sample preparation can take hours to a full day, depending on the laboratory and total sample throughput. During the preparation process, the laboratory will include samples from the impaired drivers and quality controls (QC). The QC serves as the fact-checker for the run. Blood and urine QC contain known amounts of alcohol in each matrix tested. The QC samples are interspersed throughout the run to span the breadth of the testing for that sample batch.
In addition to QC samples, an internal standard is introduced into every sample. This is a known amount of a volatile that does not interfere with alcohol, such as n-propyl alcohol, to show consistency throughout the run. The internal standard should be consistent in every result. If not, this points to an issue in the run that could be due to the sample or the instrument. The same applies to the QC; if the concentration reported in the QC is not within the specific parameters established by the QA plan, the run must be evaluated and, if possible, samples may need to be prepared again or rerun on the instrument. Either way, an investigation occurs to determine why there is a discrepancy. In addition to QC, internal standards, and calibration as measures of testing integrity, every sample must be run in duplicate. This could be done by the same analyst on the same day but on a separate run or another day in an individual run. The results of the duplicate testing must match within a certain percentage to be considered a valid result. The laboratory will take the average of the two test results as the final reported BAC.
Once the run is complete, the analyst must review the data and provide the results in an operating system called the Laboratory Information Management System (LIMS). LIMS holds the information on each sample as provided upon submission and any testing results. LIMS is a secure location to retain all the information and testing results; only approved laboratory individuals can access it. Upon review of the data, the run data are then supplied to another laboratory individual, often called the technical reviewer. The reviewer will examine the data from the run, ensure the instrument calibration is correct, verify the internal standard and QC are aligned with the required specifications, check the chromatography of the analytes, and ensure the concentrations from the instrument data are correctly transferred into the LIMS. Once the analyst’s work has been reviewed, then the result is considered complete and may be reported. If all goes smoothly and there are no interruptions, such as court testimony or other absences from the lab, this entire process can take two to three days for the BAC testing.
The same QA plan is applied when performing drug testing, which is much more complex than BAC testing. Because each laboratory uses different sample preparation techniques and instrumentation, the workflows and subsequent turnaround time can vary drastically. Most laboratories will complete the BAC testing and then proceed to drug testing. Approximately half of the forensic toxicology laboratories apply a stop-testing policy to their impaired-driving cases. This policy dictates whether or not drug testing will occur based on the resulting BAC. Many laboratories have chosen 0.08 g/100 mL as their alcohol limit to perform drug testing, while others use 0.100 g/100 mL. Stop-testing policies are in place due to the lack of laboratory resources to conduct drug testing. Unfortunately, the stop-testing policies are the most significant contributor to the underreporting of impaired drivers.
If drug testing is conducted, the sample is first put through a screening process. Some laboratories use immunoassay to perform the screening test. Immunoassay provides positive or negative results for drug classes; in some instances, it can identify a specific drug, but most commonly, the test looks for drug classes such as benzodiazepines, opiates, etc. Another screening method used by laboratories, called mass spectrometry, is much more specific. Depending on the capability of the immunoassay, laboratories may need to use a combination of mass spectrometry and immunoassay for thorough drug screening. The QA plan is applied to the screening process, including QC, PT, and technical review at every step.
A positive screening result must be confirmed. The confirmation process will verify the drug’s identity and, in many cases, provide a concentration. If a sample contains multiple drugs from different drug classes, several confirmation tests on various instruments may be required. As with the BAC and screening tests, confirmatory drug testing must follow the QA plan, and technical review must occur. You can imagine that if you were to have a sample with five drugs, all from different classes, this would require five different tests. The testing time includes sample preparation, instrument run time, initial review of the data, entering information into the LIMS, and technical review and reporting. One sample will take days to weeks for the testing to be complete if all time and effort can be focused on that one sample and its necessary tests. However, this is unrealistic, and samples are not followed from beginning to end in days or weeks. Laboratories must batch multiple samples together to make the testing the most efficient in cost and time. This often will require multiple analysts working on the same sample for many laboratories.
The Negative Drug Report
Because not all forensic toxicology laboratories perform the same testing, it has been challenging to quantify the impaired-driving issue appropriately. Many laboratories lack the newest instrumentation to identify new and emergent drugs or detect more common drugs at lower concentrations. Sometimes, the law enforcement officer has determined the driver is too impaired to operate a motor vehicle safely, and the toxicology testing reveals that no drugs were detected.
There are two situations in which this may occur: Either the drug or drugs impairing the individual are those for which the laboratory cannot test or the laboratory could not report the drug because it was below the cutoff testing limit required by their accreditation and method validation. Drug trends are constantly changing, making it difficult for laboratories to detect them without new, innovative technology. The same goes for the drug testing cutoff limits. Laboratories with older instrumentation may not be able to detect specific drugs at low enough concentrations. Remember, the time the blood was drawn differs from when the impairment was observed. The closer the blood draw can occur to the time of driving, the more representative the drug concentrations are for the impairment observed.
For example, delta-9-THC is one of the impairing compounds in cannabis. After consumption, delta-9-THC concentrations in the blood rise quickly and sharply, and elimination occurs soon after that. In an impaired-driving investigation, the impairment the law enforcement officer observes at the roadside will not be appropriately reflected in the delta-9-THC concentration in the blood. In some cases, the time from the impaired-driving stop to the blood draw is enough for the delta-9-THC to dissipate to a point at which the laboratory is unable to report the concentration, thereby providing a negative drug result. The absence of a drug result could mean the impairment observed is from something other than a drug, or it could mean that the laboratory could not detect or report the drug.
Forensic Toxicology Testing— Results Interpretation
When interpreting toxicology results, the sample matrix collected, such as blood, urine, or oral fluid, should be considered. Drug concentrations in urine samples should not be used to interpret impairment. Drugs can accumulate in the urine over time, making it challenging to determine the recency of use. Urine is simply a matrix used to determine a history of drug use.
Oral fluid is quickly becoming a reliable matrix that can be used in impaired-driving investigations. There are two types of testing for drugs in oral fluid: roadside and laboratory-based testing (LBT). Several roadside devices are available to detect drug classes in oral fluid at the roadside. These are not considered evidentiary, but a tool law enforcement may use to assist in impaired-driving investigations. Laboratory- based testing is for oral fluid collected at the roadside, and the subsequent testing is performed in a laboratory. Only a few LBT oral fluid programs exist currently in the United States. However, many states are examining the potential of including oral fluid in their impaired-driving testing. Oral fluid may be particularly interesting for law enforcement agencies with difficulty getting blood drawn as quickly as possible.
Whole blood is the gold standard for sample matrix in forensic toxicology. Most drugs are stable when collected in the graytop collection tubes; however, some drugs lose their stability over time. Preparing the blood sample to be tested on an instrument takes laboratory time, but the utility of interpreting drugs in blood is the most reliable. Whole blood provides a snapshot of what drugs were circulating throughout the body when the blood was drawn. Therapeutic ranges have been established for most scheduled drugs and can be helpful when interpreting concentrations in blood. It is important to remember that therapeutic ranges guide therapy dosing. They do not determine impairment. Many drugs impair, even when the concentration is within the therapeutic range.
Testimony in BAC cases involves the receipt of the sample to the laboratory and its condition; the method used to test the blood for alcohol, which includes the assurance that it was alcohol measured and not any other volatile such as isopropanol or the inhalant 1,1-difluoroethane. If appropriate, the analyst may continue further to testify regarding the effects of alcohol on the human body and what signs of impairment may be present. Several publications and scientific organizations have position statements indicating that all individuals with a BAC of 0.08 g/100 mL are impaired; however, the degree of impairment will vary. The experience level and ability to testify to impairment may differ for each analyst. The expertise in interpreting drug testing results varies across the forensic toxicology discipline. While alcohol is well understood and studied to be able to state that at 0.08 g/100 mL, some level of impairment exists, we cannot make the same conclusion when it comes to drugs and their concentrations in blood.
BAC estimation using retrograde extrapolation calculations based on the toxicology result has been used in forensic toxicology for decades. The ANSI/ASB recently released a best practice recommendation for performing retrograde extrapolation to estimate BACs. The document, ASB 122, guides how best to perform the calculations and their application in court. Retrograde extrapolation has been shown through years of study to be a reliable way to provide a BAC estimate at a time before the chemical test. When interpreting BAC results, analysts must rely on their testing methods and overall QA plan to ensure the result is reliable.
Interpretation and testimony of drug results are far more complex than BAC results. In some jurisdictions, analysts cannot testify on anything other than the test result and the supporting, underlying QA plan. For others, they can provide not only result information but also the interpretation of the drugs identified. The ANSI/ ASB 037 document, Guidelines for Opinions and Testimony in Forensic Toxicology, provides a boundary within which all forensic toxicologists, defense and prosecutorial, must maintain their testimony.
Unlike BAC and retrograde extrapolation calculations, using calculations to estimate drug concentrations is prohibited in forensic toxicology, as stated in ANSI/ ASB 037. It is not possible to determine a drug concentration at a time before the blood is drawn. Complex metabolic pathways, route of administration, co-ingestion of drugs, and tolerance all play a role in drug metabolism, making it impossible to estimate a concentration at an earlier point in time. The forensic toxicologist may provide information about the drugs identified, standard dosages, typical uses, intended and unintended side effects, what the body does to the drug (pharmacokinetics), and what the drug does to the body (pharmacodynamics). They also can opine about impairment from the drugs detected in the context of the case using observations from law enforcement.
Understanding the breadth and limitations of forensic toxicology and its testing is essential to realize the role of the laboratory in an impaired-driving investigation. Laboratory testing is not a mechanism to identify impairment. However, the testing can be used to correlate the drugs found with observations from the law enforcement officer. A forensic toxicologist should never state that a particular person is too impaired to operate a motor vehicle. They may speak in generalities as they relate to the average person and provide context to the impairment witnessed, but the toxicologist was not there when the driver was evaluated.
Forensic Toxicology—A Path Forward
The RTL program has succeeded in communication, collaboration, testing scope expansion, and training for forensic toxicology laboratories and highway safety partners in the states they represent. Working with the Judicial Fellows and Regional and State Judicial Outreach Liaisons has allowed the RTLs to reach out to judicial professionals in a way that never existed before. In addition to the judiciary, other partners such as law enforcement, state highway offices, and treatment court providers have played a key role in collaboration, training, and communication. There is a long way to go to move the needle on better understanding impaired driving and, just maybe, breaking the cycle. Still, the push to reframe forensic toxicology as a partner in public health instead of a piece of the criminal justice system will significantly reduce recidivism. We know knowledge is power, and combining efforts and learning from one another are the most incredible ways to increase our understanding of our roles in impaired driving.