by: Nachman Brautbar
"Intoxication, Drugs of Abuse Testing
& Forensics Application
By Nachman Brautbar, M.D.
The list of agents which can cause false positivity in the urine has also been described for endogenous excretion of enzymes in the urine. For instance, a study from Emory University by Dr. James Woodford, has shown that a percentage of persons of African origin, orientals and Pacific Islanders may be testing positive for marijuana secondary to a mechanism which involves the pigment melanin which protects the skin from sun, which approximates the molecular structure of the THC metabolite which causes laboratory cross reaction with marijuana.
What this means is that if you have used any of these over-the-counter medications, you may be accused (arrested) based on a false positive urine test. If your expert does not pick this up you may be in serious irreversible trouble.
Methodology of Drug Screening in Urine
There are several methods to detect drugs in the urine. The most frequent one is an enzyme immunoassay (EIA), or radioimmunoassay (RIA), and florescence polarization immunoassay (FPIA). There are additional more sophisticated methodologies which are performed on extract of urine which are performed using thin layer chromatography (TLC), gas chromatography (GC) high performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GS/MS). The only accepted procedures based on the definition of the National Institute of Drug Abuse (NIDA), and the Department of Defense (DOD), are immunoassays followed by gas chromatography/mass spectrometry confirmation. The confirmation utilizing gas chromatography/mass spectrometry is required since the methodology of immunoassay can give false positive results due to cross reactivity. This is due to the fact that this methodology cannot specifically identify the drug, but rather the antibodies recognize substances which may have the same structure chemically, or immunologically or enzymologically, other than the drug of interest. Immunoassays for amphetamines will show reactivity with drugs structurally related to amphetamines, such over-the-counter sympatomedicoamines, phenylpropanolamine and ephedrine, over-the-counter legal medications used for nasal congestion, cold and appetite suppressant. Confirmation therefore is a must utilizing gas chromatography/mass spectrometry. The use of gas chromatography/mass spectrometry provides an extremely high index of reliability when properly preformed and applied.
As far as gas chromatography/mass spectrometry, this is a superb methodology if done correctly. For instance, if the equipment has not been cleaned appropriately, the previous run from the previous testing will contaminate the next sample, and will give erroneous, inaccurate and incorrect results. Therefore, it is mandatory to look into the methodology that the person used for specific results on gas chromatography/mass spectrometry at a given indicated case. (On many occasions a deposition of the lab technician will reveal that the sample was contaminated.)
What this means to you is that if your urine is tested utilizing the immunological method only, without confirmation with GS/MS, there is a high probability that the result may be a false positive and irrelevant to your situation.
Related Articles
"Intoxication, Drugs of Abuse Testing
& Forensics Application
By Nachman Brautbar, M.D.
The list of agents which can cause false positivity in the urine has also been described for endogenous excretion of enzymes in the urine. For instance, a study from Emory University by Dr. James Woodford, has shown that a percentage of persons of African origin, orientals and Pacific Islanders may be testing positive for marijuana secondary to a mechanism which involves the pigment melanin which protects the skin from sun, which approximates the molecular structure of the THC metabolite which causes laboratory cross reaction with marijuana.
What this means is that if you have used any of these over-the-counter medications, you may be accused (arrested) based on a false positive urine test. If your expert does not pick this up you may be in serious irreversible trouble.
Methodology of Drug Screening in Urine
There are several methods to detect drugs in the urine. The most frequent one is an enzyme immunoassay (EIA), or radioimmunoassay (RIA), and florescence polarization immunoassay (FPIA). There are additional more sophisticated methodologies which are performed on extract of urine which are performed using thin layer chromatography (TLC), gas chromatography (GC) high performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GS/MS). The only accepted procedures based on the definition of the National Institute of Drug Abuse (NIDA), and the Department of Defense (DOD), are immunoassays followed by gas chromatography/mass spectrometry confirmation. The confirmation utilizing gas chromatography/mass spectrometry is required since the methodology of immunoassay can give false positive results due to cross reactivity. This is due to the fact that this methodology cannot specifically identify the drug, but rather the antibodies recognize substances which may have the same structure chemically, or immunologically or enzymologically, other than the drug of interest. Immunoassays for amphetamines will show reactivity with drugs structurally related to amphetamines, such over-the-counter sympatomedicoamines, phenylpropanolamine and ephedrine, over-the-counter legal medications used for nasal congestion, cold and appetite suppressant. Confirmation therefore is a must utilizing gas chromatography/mass spectrometry. The use of gas chromatography/mass spectrometry provides an extremely high index of reliability when properly preformed and applied.
As far as gas chromatography/mass spectrometry, this is a superb methodology if done correctly. For instance, if the equipment has not been cleaned appropriately, the previous run from the previous testing will contaminate the next sample, and will give erroneous, inaccurate and incorrect results. Therefore, it is mandatory to look into the methodology that the person used for specific results on gas chromatography/mass spectrometry at a given indicated case. (On many occasions a deposition of the lab technician will reveal that the sample was contaminated.)
What this means to you is that if your urine is tested utilizing the immunological method only, without confirmation with GS/MS, there is a high probability that the result may be a false positive and irrelevant to your situation.
Related Articles
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