Can_Urine_Drug_Screens_Be_Wrong_ Can_Urine_Drug_Screens_Be_Wrong_ Can_Urine_Drug_Screens_Be_Wrong_ Can_Urine_Drug_Screens_Be_Wrong_ Can_Urine_Drug_Screens_Be_Wrong_
Can Urine Drug Screens Be Wrong:


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Can Urine Drug Screens be Wrong?

The short answer is definitely, YES!

The typical medical office urine drug screen (UDS) is what is called an immuno-assay test system.  In such systems, a urine sample is tested by exposing the urine sample to protein antibodies which are designed to detect (indicated by a color change) the presence of certain molecular structures or parts of molecules.  Therein lies the rub.  A given molecule, for example, tetra-hydro-cannabinol (THC, the active agent in marijuana), has structural components which, to an anti-body, look just like other the structures found in other molecules, such as ibuprofen or the stomach medicine, Prilosec aka omeprazole.  That's right; the anti-bodies designed to detect the presence of THC, often indicate the presence of THC when in fact THC is not present, but ibuprofen (e.g. Advil) or Prilosec (omeprazole) IS!!! That's called a false positive and it occurs with incredible frequency.  That's because ibuprofen, omeprazole and protonix, to name just a few, have  molecular components (say, a couple of methyl groups) that look just like the same couple of methyl groups in THC; parts of the molecules are the same, but the total, whole molecule is quite different.  The only way around this is to send in the sample for Mass Spectroscopy (MS) which has essentially no error, as it determines the EXACT structure of the WHOLE molecules present in the urine sample and names them.  It looks at the whole molecule, not just part, like immuno-assay does.

The second problem with the typical medical office UDS has to do with detection limits.  Some UDS systems are designed to detect as little as 5 nanograms (ng) of say, hydrocodone.  Others only detect 10 nanograms and above.  Some, require 50ng or more.  The cheaper the system, in general, the higher the limits of detection, as it is harder to detect 5ng than it is 50ng.   If your doctor has a UDS system that only detects 50ng or more of hydrocodone, and you haven't taken yours since a few days ago, you'll probably have a negative drug screen because not enough hydrocodone is present in your urine to be detected by the system used for detection.  That's called a false negative.  The system says negative, when the drug really is present, but in too small an amount for the system being used to detect it.  Another example involves the new pain control patch medications, butrans or buprenorphine, which is placed every week at one of four body sites.  The medication in the patch is hard to measure.  Almost no UDS systems measure it as an opiate and even most labs using MS can't detect it unless specifically asked to do so.  Many patients are discharged from their doctor's care because they are prescribed the butrans patch, they're drug screened with an office UDS, and it does not show up.  The problem is that the UDS can't measure the low amount of buprenorphine present.  But most doctors simply don't know this, and the patient gets discharged for non-compliance.

Obviously the whole domain of drug screening is very complex.  That's why only physicians should use these systems as they should know the issues of false positives and false negatives, as well as the basic principles of laboratory medicine.  Under no circumstances should lay employers, school personnel, or court workers (e.g. probation officers) be allowed to use and interpret UDS systems, as they have no idea what they're doing and run the risk of mis-interpretation of UDS results, and may accidently ruin peoples' lives. 



 

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