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.
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.
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.
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.
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.
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.