Frequent Questions

Our toxicology experts have resolved questions and concerns for thousands of customers. The information found on this webpage can help answer many common questions, and assist you in managing a substance abuse testing program. The questions listed here are constantly updated, expanded, and refined to ensure that you have access to the very latest information. Begin by browsing the list of questions below. Click the question to reveal the answer.


Commonly asked Questions

Q: Who do I contact about a specific question?

A: Feel free to contact us whenever you have a question or need assistance with your products or service options.

  • New Account/Customer Services 800.255.2159, option 1
  • Toxicology Support Services 800.255.2159, option 5
  • Information Technology 800.255.2159, ext. 34311
  • Contact us online

Q: How long can drugs be detected in the system?

Our in-depth Drug Information Library breaks down the retention times for a wide range of drugs. Here you can find information about drug classifications, metabolism, abuse, and methods of analysis.

Q: What is specimen adulteration?

Methods to adulterate urine samples for substance abuse testing generally fall into three categories:

  1. urine substitution
  2. ingestion of fluids or compounds for flushing out the system, diluting the sample, or interfering with the testing process (OR)
  3. direct addition of adulterants to the urine specimen itself. The substitution of one's own urine sample with one which is clean is a common practice.

Q: Can passive exposure cause a positive drug screen for THC?

Passive Inhalation: In general, routine passive exposure to marijuana smoke will not result in a positive result for cannabinoids in excess of a 50 ng/mL screening cutoff and the THC-COOH (by LC-MS/MS or GC-MS) is in excess of 15 ng/mL.

Q: Why are screening and confirmation cutoff levels different?

Screening and confirmation testing are performed using different methodologies that necessitate different cutoff levels. The cutoff levels of an immunoassay screen are typically higher than those of a more sensitive GC-MS or LC-MS/MS confirm test, because they screen for a larger group of parent compounds, metabolites and other structurally similar compounds.

If an immunoassay test detects a drug (above the screening cutoff level) the presumptive positive specimen may be sent to GC-MS or LC-MS/MS confirmation testing. Many times, these individual compounds are present in concentrations much lower than the total immunoassay response, thus resulting for the cutoff levels being lower for the GC-MS or LC-MS/MS test.


Rapid Screening Device Questions

Q: How do I use my rapid screening devices?

Our in-depth and interactive device training procedures will ensure you and your agency perform effective drug screens in a manner consistent with manufacturer recommendations. Once you've completed the device training, take a quiz to test your knowledge of a specific device. If you pass, you'll receive a Product Training Certificate*.

*PRODUCT TRAINING CERTIFICATE: RTL's product training certification ensures that collection, device testing and result interpretation are performed in a manner consistent with manufacturer recommendations. RTL's product training certification is NOT an accredited proficiency certification for DOT or workplace specimen collection/testing. Contact DATIA, SAPAA or Office of Drug & Alcohol Policy & Compliance (DOT) for more information on specimen collection/testing certification.

Q: Do the rapid test results hold up in court?

The on-site device provides only a preliminary analytical test result. A more specific analytical method, preferably liquid chromatography/tandem mass spectrometry (LC-MS/MS) or gas chromatography/mass spectrometry (GC-MS), must be used to obtain a confirmed analytical result. Any result, which is contested or used punitively, and especially, if taken to court, must be confirmed. To setup a laboratory confirmation account, contact your sales representative at 800.255.2159.

Q: How do I know if the test device is negative?

If the test is negative, lines appear in the control region (C) and next to each particular drug name in the test region. The negative result indicates that the drug concentration is below the detectable cutoff level. The shade of line in the test region will vary, but it should be considered negative, even if there is a faint line.

IMPORTANT PROCEDURE NOTE: Refer to the manufacturer's product insert for complete instructions, limitations, and warnings.

Q: How do I know if the test device is positive?

If the test is presumptive positive, lines appear in the control region (C), and no line appears in the test region next to a particular drug name. This positive result indicates that the drug concentration is above the detectable cutoff level. All positive results are presumptive and should be confirmed by an alternate method (e.g. LC-MS/MS or GC-MS).

Q: How do I know the test device is working properly?

A control line will be present if the test is working properly. If a control line does not appear, repeat the test with a new device. Insufficient specimen volume or incorrect procedural techniques are most likely the reasons for control line failure. Review the procedure and repeat the test using a new device. If further assistance is required, please contact RTL via our toll-free hotline 800.255.2159.

Q: What is the shelf life of the on-site screening devices?

The on-site screening devices have a shelf life of up to 24 months from the date of manufacture. The expiration date is indicated on each individual foil pouch and can be used up until that date.

Q: How many on-site test devices come in a box?

Typically there are 25 on-site screening devices in each box.

Q: Do the screening devices need refrigeration?

No, as stated on the "Storage and Stability" section of the product insert, the test device should be stored at 2° to 30C° (36-86°F) and will be effective until the expiration date.


Laboratory Testing Questions

Q: What laboratory technology and equipment does RTL utilize?

Our leading-edge equipment and proven methodologies help us "find out". You can depend on RTL to utilize the most sensitive equipment, proven processes and highly skilled personnel to deliver timely, accurate and reliable results. We'll find out—using the optimal combination of gas chromatography/mass spectrometry (GC-MS), liquid chromatography/tandem mass spectrometry (LC-MS/MS) and enzyme immunoassay (EIA).

Q: How do I collect a specimen for laboratory confirmation?

Laboratory drug and alcohol test results are often used in legal proceedings. The manner in which specimens are collected and handled is very important. Specimens must be handled and controlled by collection site personnel throughout the collection process. Redwood Toxicology Laboratory provides suggested specimen collection and labeling guidelines. It is the responsibility of individual collection agencies to adopt their own policies and procedures according to their needs in compliance with individual state and federal regulations.

An instructional Reference Guide will be included with your first order of lab supplies. Please read these instructions carefully.

Q: How do I ship a specimen to the laboratory?

You can send a rapid on-site collection device (presumptive positives only), or you can send specimens collected using an appropriate urine or oral fluid container. Please follow the link below to review our Specimen Labeling and Shipping guidelines.

An instructional Reference Guide will be included with your first order of lab supplies. Please read these instructions carefully.

Q: When can I expect to see the drug test report?

Urine screening results are typically available within 24 hours1 of receipt of the specimen, while oral fluid screen results take 24-48 hours1. Presumptive positive specimens are usually confirmed (unless they are "Screen Only") within 24-72 hours depending on the method. Confirmation of specimens that are presumptive positive by rapid/on-site devices take a minimum of 48 hours.

We offer numerous reporting options including our powerful and convenient ToxAccess Result Reporting system. With ToxAccess you can track specimens every step of the way—from collection to reporting—in real time, 24/7.

1. Excludes specimens received Saturday.

Q: What does ng/mL mean?

Drug testing cutoff levels are usually expressed in the units of measure ng/mL (nanograms per milliliter). A quantitative positive GC-MS or LC-MS/MS result is commonly expressed in ng/mL.

Q: How long does RTL store the specimen?

RTL stores positive oral fluid and urine specimens for three (3) months. Negative specimens are kept for 48 hours.

Urine laboratory testing

Q: What are the urine screening cutoffs and methodologies?

RTL screens urine specimens by enzyme immunoassay (EIA). 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 positive or negative result, indicating the presence or absence of detectable drug metabolites above a specific cutoff level.

Q: What are the urine confirmation cutoffs and methodologies?

Confirmations are available by gas chromatography (GC), gas chromatography/ mass spectrometry (GC-MS) and liquid chromatography/mass spectrometry/mass spectrometry (LC-MS/MS). Based on your agency's account settings, specimens may be confirmed by one or more of the aforementioned methods. GC-MS and LC-MS/MS provides identification of the molecule(s) based on characteristic fragmentation patterns at specific retention times.

Q: What is the importance of checking the urine temperature strip on the collection cup?

Under normal situations fresh urine will display a temperature between 90 and 100 degrees Fahrenheit on the temperature strip, if read within 4 minutes of the collection. Should the temperature strip not register, the specimen should be immediately re-checked using a new cup (or strip) and the results recorded on the requisition. Specimens with a temperature out of range may indicate a substituted or adulterated sample.

Q: What is the importance of checking urine creatinine levels?

Creatinine is a metabolic by-product of muscle metabolism, and normally appears in urine in relatively constant quantities over a 24 hour period with "normal" liquid intake. Therefore, urine creatinine can be used as an indicator of urine water content (dilution) or as a marker identifying a specimen as urine. Greater than normal intake of water will increase the urine water content (lowering the creatinine level) consequently diluting any drug which may be present in urine. Conversely, a limited intake of water can lead to an abnormally concentrated urine specimen (as occurs with dehydration) resulting in elevated creatinine levels.

» Click here to learn more

Oral fluid laboratory testing

Q: What are the oral fluid screening cutoffs and methodologies?

Specimens collected with the oral fluid collection device are sent to RTL for screening by Enzyme Immunoassay (EIA). Positive screens, other than methadone, are confirmed by gas chromatography/mass spectrometry (GC-MS). The analytical methods used by RTL for the detection of drugs of abuse are scientifically accepted and approved by the U.S. Department of Health and Human Services.

» Screening Cutoff Levels and Methods

Q: What are the oral fluid confirmation cutoffs and methodologies?

Specimens collected with the oral fluid collection device are sent to RTL for screening by Enzyme Immunoassay (EIA). Positive screens are confirmed by gas chromatography/mass spectrometry (GC-MS). The analytical methods used by RTL for the detection of drugs of abuse are scientifically accepted and approved by the U.S. Department of Health and Human Services.

» Screening Cutoff Levels and Methods

Q: What are the oral fluid drug detection times?

The drug detection times in oral fluid closely parallel those in blood. In general, Amphetamines, Barbiturates, Benzodiazepines, Opiates, Cocaine/Benzoylecgonine, Methadone, and PCP can be detected for up to 48 hours1 following use. Parent THC (marijuana) can be detected in oral fluid for up to 24-48+ hours1.

1) Average detection times.

Q: I suspect my donor used a substance of abuse, how long should I wait before collecting a specimen?

Depending on the drug and dosage, drugs may be detected in oral fluid in as little as a few minutes or up to approximately 2 hours from the time of use.

Q: Why are the drug levels in oral fluids lower than those in urine?

Oral fluid drug levels largely correlate with the amount of drug in the blood (dependent on the saliva/plasma ratio for each drug). Higher drug and drug metabolite levels are found in urine because they are concentrated by the kidneys during the excretion process


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