Acid Med Giving False Reading for Thc

Inquire the Expert: May 2015

Q: Can you explain the reason for a imitation-positive urine drug screen for marijuana?

A: In 2013, an estimated 19.8 million Americans aged 12 years or older were current (by month) users of marijuana and 8.1 meg were daily users.¹ An analysis of 7.half dozen one thousand thousand urine drug screens performed in the U.S. workforce, indicated the positivity rate for marijuana was i.seven%.² A positive urine drug screen (UDS) can have an bear upon on a person'due south life, so it is important to ensure the result is authentic.

Tetrahydrocannabinol (THC) is the active ingredient of marijuana, however UDS test for the metabolite 11-nor-delta-9-tetrahydrocannabinol-nine-carboxylic acid (THC-COOH).^3-5 A UDS does non prove there is an exact amount of the metabolite in the urine but indicates the metabolite concentration is in a higher place a given theshold.

UDS is an immunoassay test that uses antibodies to detect presence of specific drugs or metabolites. It is the most common method for initial screening. Advantages of the immunoassay exam include the capability for big-scale screening and rapid detection, but the disadvantage is the potential for false-positive results.⁴ A rapid UDS for marijuana is performed using a threshold of fifty ng/mL.⁶ If a test comes back positive, a more specific gas chromatography-mass spectrometry (GC-MS) test, which uses a threshold of fifteen ng/mL, can be performed to confirm the positive issue.^vi

The GC-MS test is considered the "gold standard" of confirmatory tests due to its power to observe minor quantities and confirm the presence of a specific drug. Advantages include high accurateness and sensitivity. Disadvantages include the amount of fourth dimension it takes for the exam to exist completed, the high expertise level required to perform the test, and the price of the test.^iv

An important aspect to accept into consideration when trying to determine if a positive marijuana UDS is false is how long marijuana can exist detected in the urine. Factors that may influence the length of time a drug will be detectable include the frequency of drug use and the fourth dimension of last ingestion. A unmarried use of marijuana is typically detectable for iii to 7 days, moderate use can be detected for five to 7 days, daily use for 10 to 15 days, and long-term/heavy employ for over a month.⁴ It also is important to go on in mind that people may endeavor to add products, such as heart drops (Visine),⁷ to their urine to cause a fake negative.

False-Positive Screens

Passive marijuana inhalation has been thought of as a potential reason for a false-positive marijuana UDS. Three studies were performed to analyze this theory: one with participants exposed to secondhand smoke in a pocket-sized enclosed room for
one hour, another study with participants exposed to the smoke daily for 3 consecutive days, and the 3rd study was with participants exposed to smoke in a small, closed station wagon. Eighty unlike urine samples were analyzed; only 2 samples exceeded the 20 ng/mL threshold used in their immunoassay examination—and those only barely.⁸

Based on the results of these studies, a positive result for marijuana due to passive inhalation would exist highly unlikely when using the standard threshold of 50 ng/mL for initial screening.

Another potential source of UDS interference is thought to be the use of not-steroidal anti-inflammatory drugs (NSAIDs). One report evaluated 3 drugs (ibuprofen [Advil, Motrin, others], naproxen [Aleve, Naprosyn, others], and fenoprofen [Nalfon, others]) in patients taking them chronically or acutely. The authors theorized that NSAIDs would interfere with the immunoassay examination through interference with the enzyme reaction, production of erroneous absorbance reading, or secretion of an endogenous substance that inhibits cannabinoid binding to an antibody. Of the 510 urine samples collected from 102 participants, 10 samples (0.02%) tested positive for cannabinoids. Follow-upward GC-MS tests showed that viii of the ten samples (80%) were truthful positive for cannabinoids. Of the 2 samples that were positive due to NSAID use, ane was from acute ibuprofen use (1,200 mg in one mean solar day), and the other was from chronic naproxen employ (1,000 mg daily for no longer than 30 days).⁹ This study shows it is unlikely for NSAIDs to cause a simulated-positive marijuana UDS.

In addition to NSAIDs, efavirenz (Sustiva) is some other medication thought to interfere with UDS for marijuana. In a study looking at patients who were taking efavirenz 600 mg daily as an antiretroviral handling for at to the lowest degree 14 days, 28 out of xxx participants had a simulated-positive UDS using rapid response tests. The authors believed the interference was attributed to EFV eight-glucuronide, one of 2 major urinary metabolites of efavirenz.^five One limitation to this study is the failure of the authors to mention other medication apply such as the synthetic cannabinoid dronabinol (Marinol, others), which has been shown to cause a fake-positive in a UDS for marijuana 30% to 45% of the time.^ten

Hemp Foods

Likewise NSAIDs, efavirenz, and dronabinol, hemp food consumption is also idea to exist able to cause a false-positive UDS for marijuana. Nutrient containing hemp seeds or oil can often be constitute in common cold-pressed oil for cooking, salad dressings, and capsules as nutritional supplements. Fifteen good for you participants were studied to come across the effects of consuming hemp foods daily for 10 days.³ No participants had contempo exposure to THC in hemp foods or medicinal or recreational drugs, every bit confirmed by a baseline UDS specimen.

The hemp foods contained 4 different doses of THC, with participants consuming each dose for 10 days before testing their urine. THC doses in hemp seed oil ranged from 0.09 mg to 0.half-dozen mg. At the highest dose of 0.6 mg, which is an unrealistically loftier amount for daily consumption of hemp foods, the highest measured THC-COOH concentration in urine was v.2 ng/mL, which is well beneath the GC-MS confirmation threshold of 15 ng/mL.³ This study shows that it is very unlikely for hemp nutrient consumption to interfere with an immunoassay UDS, or GC-MS.

Summary

When screening a person for possible marijuana apply, it is of import not to make assumptions from an initial result from a positive immunoassay test, and to confirm a positive effect with GC-MS. If a person is taking efavirenz, you take limited testify to suspect a simulated-positive event, whereas it is much less likely for NSAIDs, hemp food consumption, or passive marijuana inhalation to cause a false-positive result. It is important to have into consideration recent medication utilize before making a decision on how to act on a positive UDS for marijuana.

—Co-author Jeremy Grayness, PharmD Candidate

Concluding updated on: April 17, 2017

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Source: https://www.practicalpainmanagement.com/resources/diagnostic-tests/false-positive-screen-marijuana

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