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Main » News Releases » Location » South Africa » Prescription Drug Efavirenz Yields False Positive Test Results For THC, Study Says[/url]

Prescription Drug Efavirenz Yields False Positive Test Results For THC, Study Says

Thursday, 01 December 2011

 

Pretoria, South Africa: Prescription doses of the antiretroviral prescription drug efavirenz (EFV) cross-reacts in urine immunoassay tests for the carboxy THC metabolite, according to clinical data published online in the journal Annals of Clinical Biochemistry.

 

Investigators at the University of Pretoria in South Africa analyzed random urine samples from 30 patients on EFV therapy for THC metabolites by two near-testing devices (THC One Step Marijuana and Rapid Response(®) Drugs of Abuse Test Strips) and two automated immunoassays (Roche Diagnostics Cannabinoids II and Beckman Coulter SYNCHRON(®) Systems THC2). THC confirmatory testing was performed by gas chromatography-mass spectrometry (GC-MS).

 

Authors reported: "GC-MS failed to detect THC metabolites in any of the samples, as did three of the four immunoassays. However, the Rapid Response(®) test strips yielded positive results in 28 out of 30 samples."

 

Separate studies have previously documented that efavirenz may yield so-called 'false positive' test results for the carboxy THC metabolite on various types of presumptive immunoassay urine tests.

 

For more information, please contact Paul Armentano, NORML Deputy Director, at: . Full text of the study, "Efavirenz interference in urine screening immunoassays for tetrahydrocannabinol," appears in Annals of Clinical Biochemistry.

 

 

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Main » News Releases » Location » South Africa » Prescription Drug Efavirenz Yields False Positive Test Results For THC, Study Says[/url]

Prescription Drug Efavirenz Yields False Positive Test Results For THC, Study Says

Thursday, 01 December 2011

 

Pretoria, South Africa: Prescription doses of the antiretroviral prescription drug efavirenz (EFV) cross-reacts in urine immunoassay tests for the carboxy THC metabolite, according to clinical data published online in the journal Annals of Clinical Biochemistry.

 

Investigators at the University of Pretoria in South Africa analyzed random urine samples from 30 patients on EFV therapy for THC metabolites by two near-testing devices (THC One Step Marijuana and Rapid Response(®) Drugs of Abuse Test Strips) and two automated immunoassays (Roche Diagnostics Cannabinoids II and Beckman Coulter SYNCHRON(®) Systems THC2). THC confirmatory testing was performed by gas chromatography-mass spectrometry (GC-MS).

 

Authors reported: "GC-MS failed to detect THC metabolites in any of the samples, as did three of the four immunoassays. However, the Rapid Response(®) test strips yielded positive results in 28 out of 30 samples."

 

Separate studies have previously documented that efavirenz may yield so-called 'false positive' test results for the carboxy THC metabolite on various types of presumptive immunoassay urine tests.

 

For more information, please contact Paul Armentano, NORML Deputy Director, at: . Full text of the study, "Efavirenz interference in urine screening immunoassays for tetrahydrocannabinol," appears in Annals of Clinical Biochemistry.

 

Great information!

 

Here's some other references people might appreciate:

 

NORML - The ABCs of Marijuana and Drug Testing (link)

 

NORML - Drug Testing Tips (link)

 

National Drug Court Institute - Fact Sheets (link)

 

CDC - Urine Testing for Detection of Marijuana: An Advisory (1983) (link)

 

"The urine test is based on detection of 11-nor-delta-9-tetrahydrocannabinol-9-carboxylic acid (9-carboxy-THC), a metabolite of delta-9-THC, which is the primary pharmacologically active component of marijuana. Studies involving humans indicate that 80%-90% of the total dose of delta-9-THC is excreted within 5 days--approximately 20% in urine and 65% in feces (1). Plasma concentrations of delta-9-THC peak by the time a smoked dose is completed and usually fall to approximately 2 ng/ml within 4-6 hours. 9-carboxy-THC is detectable in plasma within minutes after a dose is smoked and remains in plasma considerably longer than THC itself. Urine from marijuana users contains quantities of 9-carboxy-THC in both free and conjugated form, as well as other cannabinoids (THC and its metabolites) detectable by the test."

 

"When the manufacturer's instructions are followed, urine samples containing at least the stated detection level of 9-carboxy-THC will test positive at least 95% of the time. In a CDC field-test survey of 64 laboratories, those using the SYVA system for urine screening for cannabinoids had an incidence of 4% false-positive results (2); whether these errors were analytical or clerical in nature was not determined. The manufacturer states that any positive test result should be confirmed by an alternative method."

 

Mayo Clinic - Urine Drug Screening: Practical Guide for Clinicians (2008) (link)

 

"Urine, blood, hair, saliva, sweat, and nails (toenails and fingernails) are some biological specimens used to perform laboratory drug testing, and they provide different levels of specificity, sensitivity, and accuracy. Urine is most often the preferred test substance because of ease of collection. Concentrations of drugs and metabolites also tend to be high in the urine, allowing longer detection times than concentrations in the serum allow."

 

"Two types of [urine drug screenings] are typically used, immunoassay and gas chromatography-mass spectrometry (GC-MS). Immunoassays, which use antibodies to detect the presence of specific drugs or metabolites, are the most common method for the initial screening process. Advantages of immunoassays include large-scale screening through automation and rapid detection ... immunoassay techniques are used in many home-testing kits or point-of-care screenings."

 

"The main disadvantage of immunoassays is obtaining false-positive results when detection of a drug in the same class requires a second test for confirmation. Results of immunoassays are always considered presumptive until confirmed by a laboratory-based test for the specific drug (eg, GC-MS or high-performance liquid chromatography)."

 

Table 1 = "Federal Workplace Cutoff Values" (link)

 

Table 2 = "Length of Time Drugs of Abuse Can Be Detected in Urine" (link)

 

"The urine specimen temperature should be recorded within 4 minutes of collection; the temperature should be 32°C to 38°C initially and can remain warmer than 33°C for up to 15 minutes. Temperatures outside this range can indicate that a substituted urine sample was used. The pH for normal urine fluctuates throughout the day but usually is in the range of 4.5 to 8.0. Specimen contamination should be suspected if the pH level is less than 3 or greater than 11 or if the specific gravity is less than 1.002 or greater than 1.020.16 Creatinine concentrations in normal human urine should be greater than 20 mg/dL. Urinary creatinine concentrations of less than 20 mg/dL are considered dilute, whereas concentrations of less than 5 mg/dL are inconsistent with human urine.10 Urinary nitrite levels should be less than 500 μg/mL. If adulteration is suspected or results fall outside these ranges, another specimen should be collected under direct, observed supervision."

 

"The substance THC has high lipid solubility, resulting in extensive storage of the drug in the lipid compartments of the body. This lipid solubility is associated with slow excretion of the drug and its metabolites into the urine. A single use of marijuana can result in positive urine tests up to 1 week after administration, whereas long-term use can produce positive results in the urine up to 46 days after cessation.""

 

"Other agents that have been shown to cross-react with cannabinoid immunoassays include efavirenz and proton pump inhibitors. Efavirenz, a nonnucleoside reverse transcriptase inhibitor, has been extensively reported in the literature to cause false-positive results for THC. Some speculate that the metabolite of efavirenz leads to interference with the antibody complexes in the immunoassay."

 

"People using THC often attempt to manipulate the urine to produce negative results. Addition of Visine eyedrops to urine samples has been shown to cause false-negative results for THC. Chemical analysis of Visine eyedrops has shown that the ingredients, benzalkonium chloride and the borate buffer, can directly decrease the concentration of 9-carboxy-THC in the urine with no effects on the antibodies in the immunoassay. However, these ingredients do not chemically alter 9-carboxy-THC, which will still be detected by GC-MS."

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STOP -

 

"GC-MS failed to detect THC metabolites in any of the samples, as did three of the four immunoassays. However, the Rapid Response(®) test strips yielded positive results in 28 out of 30 samples."

 

So you can fool a takehome test or field test, but not the doctor's office.

 

 

DN

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STOP -

 

"GC-MS failed to detect THC metabolites in any of the samples, as did three of the four immunoassays. However, the Rapid Response(®) test strips yielded positive results in 28 out of 30 samples."

 

So you can fool a takehome test or field test, but not the doctor's office.

 

 

DN

 

Correct. While efavirenz and proton pump inhibitors will cause false positives on immunoassays, all positive screening tests MUST be followed up by a gold-standard test (GC-MS, LC-MS) to prove consumption. Also, for those with Marinol prescriptions that are on probation and have been ordered to discontinue cannabis use, advanced laboratories potentially have the capability to look for metabolites of non-THC-cannabinoids that would only be present only in those consuming cannabis.

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