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    Why Clonazepam produces false negative in drug screens.
    avatar
    pcrx58 posted:
    Question:
    I know it is metabolized through the liver, excreted through the kidney and less than 2% of whole clonazepam is found in the urine. It is fast absorbing, protein-binding and has 90% absolute bioavailability, and maximum concentration is reached in 1-4 hours.
    Answer:
    Insensitivity of benzodiazepine screen: clonazepam (Klonopin) frequently negative on both EIA(Enzyme Linked Immunoassays) and GC/MS (Gas chromatography Mass Spec).
    Why does clonazepam in urine screen negative for benzodiazepines, yet confirm positive?
    Clonazepam is present as a metabolite in urine. It does not react well by the commercially- available screening reagents. ie EIA UDS. It is not recognized well by the benzodiazepine antibody. Therefore, clonazepam metabolite is quantitated separately by LC/MS/MS to assure that it is detected at a very small concentration.
    Why is LC/MS/MS a better confirmation technique than GC/MS? (heat)
    Gas chromatography/mass spectrometry (GC/MS) requires the drugs of interest to be put in the gas or vapor phase. This requires heating to very high temperatures. Sometimes it is additionally necessary to treat the sample with other chemicals (derivatizing agents) in order to get the drugs sufficiently able to be volatilized. This can result in loss of much of the analyte due to chemical instability at high temperatures. Thus much drug can be lost, and limits of detection are compromised. In addition, once volatilized into the gas phase, many drugs take a long time to go through the column of the gas chromatograph. Thus run times are long, and again much compound can be lost to thermal instability.
    In liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) the compounds travel underivatized through a chromatography column in solution at or near room temperature. Nothing has to be volatilized, there is no degradation due to heat, and the run time through the columns is very fast-no more than 5 minutes. The LC/MS/MS is much more sensitive than the GC/MS.
    1. Urine Drug Screens using EIA (Enzyme Linked Immunoassays) can cause false negative results for Klonopin b/c of decreased sensitivity of this test.

    2. Drug Screens for Klonopin using GC/MS also have inherent problems in the methodology b/c of having to heat the compound to get it into the gas phase, and the long travel time of the gas in the column. Just to name a couple of problems. So can also result in a false negative or a false low result.

    3. Another test method is LC/MS/MS which is better for Klonopin b/c it is more sensitive. The reason is that its done at room temperature (no loss due to heating) and the travel time to get a test result is much shorter than GC/MS.

    Klonopin is harder to detect than other benzodiazepines. After a couple weeks of usage you will be at what we call a steady state which means you have steady serum levels and will be excreting the same amount of Klonopin per day as you ingest. The lab I use lists 781ng/ml as it's threshold sensitivity for a positive urine screen for Klonopin. This means if you only excreted 1 liter of urine a day which is a fairly small quantity you would need to excrete .781mg or more of Klonopin per day to trigger a positive test. If you were excreting 2 liters of urine a day it would take 1.562mg or more of Klonopin per day to show up positive. I assume the same issue is in play for your negative serum test at your lab. As mentioned, other more expensive tests can be done to detect smaller quantities but they are usually not done routinely. Since you are taking below 1mg of Klonopin per day you could easily be below the detection threshold for the less expensive assays. Your Doctor may be ignorant of this.
    Conclusion:use LC/MS best test for Klonopin.
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