Toxicology

Please review the frequently asked questions below.
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Testing methodology

Nanograms per milliliter, abbreviated ng/mL, is the unit of measure most commonly used to express drug testing cut-off levels and quantitative test results in urine and oral fluid. A nanogram is 10-9 grams. 

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Simply stated, screening and confirmation testing are performed using different testing methodologies that have different specificity and sensitivity. The immunoassay tests used to perform initial drug screening are designed to detect a wide range of chemically similar compounds that react with the antibodies which are at the core of the chemistry making up the tests. The combined cross-reactivity of compounds in the drug class may elicit a positive response, even though an individual metabolite may be present below the initial test cutoff. When performing confirmation testing by GC/MS or LC/MS/MS, one or more specific metabolites can be identified, quantified and reported using the applicable confirmation cutoff for a positive test result. 

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Gas chromatography/mass spectrometry (GC/MS) and liquid chromatography with tandem mass spectrometry (LC/MS/MS) are the methods LabCorp uses to confirm presumptive positive drug screens. These mass spectrometric methodologies provide identification of the molecule(s) based on characteristic fragmentation patterns at specific retention times. GC/MS and LC/MS/MS are hyphenated techniques, utilizing a gas or liquid chromatograph coupled to single- or multiple-stage mass spectrometers. 

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LabCorp performs initial drug screening using immunoassay. An immunoassay is a test that uses antibodies to detect the presence of drugs and other substances in urine. The initial screening process does not measure the specific amount of drug present in urine samples. It provides either a negative or a presumptive positive result, indicating the absence or possible presence of detectable drug relative to a ‘threshold’ or ‘cutoff’ concentration. 

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Amphetamine testing

MDMA is a synthetic amphetamine structure and does cross-react with existing amphetamine immunoassays. However, the cross-reactivity of MDMA in amphetamine assays is generally less than 100%, so it may not be picked up at commonly-used testing cut-offs. To enable detection of MDMA following normal exposures, LabCorp uses reagents developed specifically for MDMA detection.2 

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Ecstasy is a commonly used street-name for MDMA (3,4-methylenedioxymethamphetamine). MDMA is an illegal drug with characteristics of both stimulants and hallucinogens. In the mid-1980s, MDMA was being used at all-night dance parties, now referred to as "raves." In 1985, the US Drug Enforcement Administration moved the drug to Schedule 1 status with no accepted medical use. 

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In order to help determine whether a methamphetamine positive may be due to an illicit source, it is helpful to determine the percentage of "d" and “l” isomers. For example, following an individual's use of Vick's Vapor Inhaler, the expected result would be nearly 100% "l" methamphetamine. Based on current laboratory guidelines, if the laboratory report indicates more than 80% "l" methamphetamine, the results are consistent with Vick's Vapor Inhaler use or one of the prescription medications metabolized to l-methamphetamine. If the laboratory reports more than 20% "d" methamphetamine present, the result indicates the use of "d" methamphetamine as either a prescription or illicit preparation. Illegally-produced methamphetamine and amphetamine may contain mixtures of "d" and "l" isomers. LabCorp recommends use of a medical review officer (MRO) to review all non-negative test results.

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Methamphetamine is available in two forms: "d" and "l." These compounds are stereoisomers (chemical mirror images). They have the same chemical formula and similar chemical properties. The "d" form is a prescription stimulant and appetite suppressant. The "l" form is available over-the-counter as the active ingredient of the Vick's inhaler and is a metabolite of certain prescription medications. Both "d" and "l" forms test positive by both immunoassay and most confirmation assays; a special d,l isomer confirmation test is available to determine how much of each form is present in a specimen.1 

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Drug detection times

See the Drug Testing Options Summary for general guidelines of drug detectability in the various testing matrices. 

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See the Drugs of Abuse Reference Guide for general guidelines of drug detectability in urine. 

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Opiate testing

According to the National Institute on Drug Abuse, "Fentanyl is a powerful synthetic opioid analgesic that is similar to morphine but is 50 to 100 times more potent. It is a schedule II prescription drug, and it is typically used to treat patients with severe pain or to manage pain after surgery. It is also sometimes used to treat patients with chronic pain who are physically tolerant to other opioids. In its prescription form, fentanyl is known by such names as Actiq®, Duragesic®, and Sublimaze®. Street names for fentanyl or for fentanyl-laced heroin include Apache, China Girl, China White, Dance Fever, Friend, Goodfella, Jackpot, Murder 8, TNT, and Tango and Cash."4 

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According to the National The National Institute on Drug Abuse, "NIDA-supported basic and clinical research led to the development of buprenorphine, a medication for the treatment of heroin addiction. These scientific discoveries spurred a collaboration with industry, which culminated in FDA approval of Subutex® (buprenorphine) and Suboxone® tablets (buprenorphine/ naloxone) in October 2002. Buprenorphine is a long-acting partial mu opiate agonist that acts on the receptor targets of heroin and morphine, but does not produce the same intense "high" or dangerous side effects. These properties also make it a good potential treatment for addiction to opiate analgesics."3 

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OxyContin® tablets are a controlled-release oral formulation of oxycodone hydrochloride generally indicated for the management of moderate to severe pain when a continuous, around-the-clock analgesic is needed for an extended period. Oxycodone is a semisynthetic narcotic analgesic classified by the US Drug Enforcement Administration as a Schedule II controlled substance with an abuse liability similar to morphine

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LabCorp offers a variety of options for opiate testing, including panels designed to detect one or more of the following: codeine, morphine, hydrocodone, hydromorphone, oxycodone, oxymorphone, methadone, buprenorphine, tramadol, meperidine and fentanyl. Your LabCorp sales representative can assist you in determining the best profile to meet your testing needs. 

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6-acetylmorphine (6-AM) is an intermediate metabolite between heroin and morphine. Generally, 6-AM is present for a short time after use of heroin. A finding of 6-AM in urine or oral fluid is a specific indication of heroin use or exposure; 6-AM has not been shown to be derived from any other source. 

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Specimen validity testing (SVT)

The nitrite result would be negative, as this level would not interfere with our testing process. The drug test(s) ordered would be conducted and reported following standard operating procedures. 

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The nitrite or oxidant threshold level established by the federal government is 200 mg/mL. This is based on the level at which a drug screen may be impacted by this type of adulterant and is higher than what would be expected from normal physiological processes. Nitrites or other oxidants > = 200 mg/mL are reported as “Invalid”. Specimens with nitrite levels > = 500 mg/mL are reported as “Adulterated”. 

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At a minimum, the SVT panel includes testing for creatinine; a creatinine < 20 mg/dL reflexes to a specific gravity test. Results of both creatinine and specific gravity are used to identify dilute, substituted or invalid specimens. Tests for pH and nitrite can also be added to a panel, and are used to assess whether the physiological parameters of the collected specimen are in the expected range

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No, specimen validity testing is performed simultaneously with the initial drug screens. Depending upon the drug screen and the specimen validity results, the laboratory will release (1) both the drug screen and the specimen validity test results, (2) the specimen validity test results only, or (3) the drug screen results only. 

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Specimen validity testing (SVT) is performed on a urine drug screen specimen to detect substitution, adulteration, or dilution. See the Drugs of Abuse Reference Guide for additional information on SVT. Use of a Medical Review Officer is recommended to evaluate out of range SVT results.

  • Substitution - Submission of a specimen that is not characteristic of human urine. Typically, this may be water or water with salt in it and is identified by extreme creatinine and specific gravity results.
  • Adulteration - Adding a substance to a specimen after it has been collected. The product added is designed to mask the presence of, or chemically destroy, the drug or drug metabolite that the specimen may contain. An adulterant product may be added with the intention of adversely affecting the testing reagents.
  • Dilution - Result of ingestion of large amounts of water typically just before urine donation or as a result of physiological conditions. If drug/metabolites are diluted to a concentration below the initial test cutoff, a dilute urine may result in a false negative.

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Frequently Asked Questions