Laboratory Drug-Testing Terminology 101 (part 1)

Dr. Joseph E. Graas, Scientific Director
Dr. Edward Moore, Medical Director

Drug Screen – a drug screen is a test used to detect either illicit or prescription drugs in a patient’s system.  Immunoassay is the most commonly used method to perform a drug screen.  A typical screen is performed either on a urine or saliva sample and produces qualitative results – either Positive or Negative – at the drug class level.

Drug Class – drugs are typically grouped into specific “families” or “classes”.  Examples of drug classes are Amphetamines, Barbiturates, Benzodiazepines and Opiates.  A urine or saliva drug screen only tests and reports the presence or absence of drugs at the drug class level.  A Positive drug screen for Opiates reveals the presence of Opiates in the patient’s system but cannot identify which specific Opiate(s) caused the Positive result.

Panel – a panel is a collection of drug screens.  A 6-panel urine drug screen might consist of testing for the classes of Amphetamines, Barbiturates, Benzodiazepines, Cocaine, Methadone and Opiates.  Panels are usually customized to each program’s and/or state’s requirements.  Additional drug screens can be added to a panel for specific samples based on program or patient needs.  For example, a screen for THC can be added to the previously mentioned 6-panel for patient John Doe (only upon request).   Results are only generated for the drugs on the specific panel; if THC is not on the panel but in the patient’s system, a positive result for THC will not be reported, as that test is not performed.

Analytes – analytes are the individual drugs within each drug class.  For example, the analytes within the Amphetamines drug class are Amphetamine and Methamphetamine. To determine which analytes are present in a urine or saliva sample, a confirmation test must be performed; this information is not available through a drug screen.

Confirmation Test – a confirmation test is used to verify the results of a drug screen.  Whereas a screen tests at the class level, a confirmatory test identifies the specific analytes present in a sample. Confirmation tests utilize different testing methodologies than those used for drug screens.  The most common confirmation methodologies are GC/MS (Gas Chromatography/Mass Spectrometry), TLC (Thin Layer Chromatography) and LC/MS (Liquid Chromatography/Mass Spectrometry).  GC/MS and LC/MS confirmations also produce quantitative results (i.e.  specific quantities of each analyte present in the sample) whereas TLC confirmations only produce qualitative results (Positive or Negative).

Retest – a retest of a urine or saliva sample is the exact same test performed a second time. If the initial test is an 8-panel drug screen, the retest will be a drug screen for the positive/negative drug in question. If the initial test is a 7-panel screen plus a GC/MS confirmation, a GC/MS confirmation will be performed for the drug(s) indicated.

Accession Number – the unique identification number assigned to each specific patient sample. When calling in to the laboratory to seek additional information about a sample or a patient’s results, providing the correct accession number allows the lab to quickly retrieve the data. 

Part 2 of this article will appear in the October issue of Toxicology Times