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Dr. D. Love
Dr. D. Love, Doctor
Category: Medical
Satisfied Customers: 18194
Experience:  Family Physician for 10 years; Hospital Medical Director for 10 years.
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Will GC /MS determine if a urine test has returned a false

Customer Question

Will GC /MS determine if a urine test has returned a false positive for THC.
Furthermore will it determine if the false positive on the initial test was due to liver/kidney problems
Submitted: 11 months ago.
Category: Medical
Expert:  Dr. D. Love replied 11 months ago.

Hello from JustAnswer.

Yes, a GC/MS will determine if a screening urine drug test returned a false positive for THC (or any drug). However, the GC/MS will not be able to identify the reason for the false positive. Not only will it not identify whether the false positive was due to liver or kidney disease, it also would not be able to determine if the false positive was due to other drugs or substances that cross-reacts with the screening test. From a medical perspective, we only care to accurately identify that the test was a false positive and really do not care why it was false positive. Once we know that it was a false positive, then we know to manage the result as if it were negative all along, and we would do that for any of the possible causes of a false positive.

If there is a clinical situation in which it is important to know whether someone has liver or kidney disease, then we would check liver or kidney lab work directly.

If I can provide any additional information, please let me know.

Dr. D. Love, Doctor
Category: Medical
Satisfied Customers: 18194
Experience: Family Physician for 10 years; Hospital Medical Director for 10 years.
Dr. D. Love and 3 other Medical Specialists are ready to help you
Customer: replied 11 months ago.
Hi Dr Love
Thanks for your re-assurance, I have been stressed to bits over this, could you embellish this more, after you read the next para.Basically my employer asked me to undergo some drug/alcohol tests, which I did. I believe a disgruntled ex-employee phoned our whistleblowing line, and reported me for smelling of alcohol on duty.
I undertook a breath test for alcohol (passed), followed by a urine test into a special beaker looking at 12 different test items. After 10 minutes there was a fail on the THC (passed all others). I am not on medication, and don`t take drugs. I am now suspended from work awaiting lab results. As a precaution I am going to my Dr to have my blood taken to see if there is anything wrong with my liver/kidneys or anything for that matter. I am assuming that my employer will use the GC/MS method of confirming the positive was actually false, from what I am reading this appears to be the "Gold Standard", is that correct? - I cannot afford to loose my job after working for them for nearly 30 years. Also can you offer any other really obvious advice from what I have written here?
Expert:  Dr. D. Love replied 11 months ago.

Yes, the gold standard is a chromatograhy/spectrometry method. Most labs use GC/MS, but there are some labs that use LC/MS or LC/MS/MS. The differences between these tests are highly technical, but any would be accurate in identifying false positives. We frequently use the term, confirmatory test, to encompass any of the various methods.

Since you are certain that you have not used marijuana, then the confirmatory test will show that it is a false positive.

I would also note that the screening tests have a fair rate of false positives, even in healthy people that are not using any other medicines, so the presence of a false positive does not typically cause a doctor to consider any evaluation for liver or kidney disease.

Customer: replied 11 months ago.
I wish I`d e-mailed you on Friday 27th May when I got suspended, you`ve certainly eased my mind. As a precautionary measure I`ll be going to see my Dr anyway, and readying my union. The company I TUPE`d across to after 27 years service, last year, are much stricter and their policy for any failed drugs/alcohol testing is dismissal.
Expert:  Dr. D. Love replied 11 months ago.

I am glad I could be of assistance.

As I said above, once the confirmatory test is negative and shows that the screening test was a false positive, it will be managed as though the test has been negative all along, so there will not be any need to implement any policy for a failed test.

Customer: replied 11 months ago.
Hi Dr Love
I still haven`t received my confirmatory test result, anyhow in the interim I have had my blood sampled, and my doctor has had a look at the results from this, he tells me there is something out of the normal going on with my liver, which will necessitate another blood sample next week, and potentially some sort of scan.
Should I be passing this information onto my employer now? or should I wait to be told the confirmatory test results?
Expert:  Dr. D. Love replied 11 months ago.

There is no need to let your employer know. In those situations in which liver disease may be the cause of the false positive, the confirmatory test will still determine that it was a false positive, so there is no need for the employer to know of the blood test that suggests that something may be going on with your liver.

As I said above, if there is concern about liver disease, then it is appropriate to pursue a proper evaluation for the liver, but that is something that your regular doctor will address, not your employer.

Customer: replied 11 months ago.
Hi Dr Love
Sorry to go on about this, anyhow, considering liver disease (abnormality) and a false positive for THC, what could the liver be producing or not producing which affects an immunoassay test. I have seen a number of websites that make the connection between liver issues and THC false positives. But nobody seems to be able to expand on why, could it be that to much lactic acid is produced, and this confuses the test?
Expert:  Dr. D. Love replied 11 months ago.

There are two substances that may be present in liver disease that appears to interfere with the screening tests, the lactic acid that you note, and an enzyme called lactate dehydrogenase, or LDH.

Customer: replied 11 months ago.
Dear Dr Love
I was informed of my lab test results today - they came back clear, this was a great relief for me and my family.
Your insight and words of advice, provided me with the re-assurance I needed to help me through this very really difficult time in my life. The sleepless nights and complete feeling of helplessness have been unbearable.
I continue to see my doctor, to follow through on the unusual blood results / liver issue.
Expert:  Dr. D. Love replied 11 months ago.

I am glad that you have finally gotten the good news and relief. Even after learning the science, it is reassuring to get the actual results.

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