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Do Screening Drug Tests Measure The Quantity Of A Particular Drug?

Posted on Tue, 26 May 2015

Question: Hi, I undergo weekly urinary drug screening for chain of custody. My declared medication is dexamphetamine 30mg/day and Antenex 10mg/day. Some days I double both the doses, other days I take nothing. For the most part I am using more than prescribed due to tolerance. I have been on dex since I was a child. I understand that cut - off levels determine a positive or negative result. Is it possible that with all the variables (eg morning there are greater amounts of metabolites than afternoon), they are able to establish quantity of the medication. If so, how. And how accurate? I'm not taking handfuls, just more than prescribed most days. Thank you.

Answered by Dr. Vivek Chail (2 hours later)

Brief Answer:
Your test shows only presence of medicine, double dose will not be measured

Detailed Answer:
Hi XXXXX,
Thanks for writing in to us.

I have read through your query in detail.
Please find my observations below.

1. Since you are regularly undergoing weekly urine drug screening, the test will only screen you for a particular drug or a group of drugs. Screening tests always measure a drug in traces and confirm it it is present or absent in a given urine sample.

2. You have rightly pointed out that there is a cut off level for positive or negative result. This means they will not measure any variation in quantity of the drug but just say yes or no in the result.

3. Since you are taking prescription drugs, the result will show the presence of the medicine. It will not show if you have taken double dose or a single dose.

Please feel free to correct any oversight in my interpretation of your problems and discuss them in detail as per your requirements.

Hope your query is answered.
Do write back if you have any doubts.

Regards,
Dr.Vivek

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Vivek Chail (3 hours later)

Thank you for that. The reason I ask is because it will be examined by a bio chemist (?) eventually.
Last week after i took 2 mercyndol for a headache the solicitor checked with the lab if the codeine result was consistent with 2 mercyndol. They confirmed yes.
So they must have some idea? Or do you think it was a guess. Thanks again.

Answered by Dr. Vivek Chail (2 hours later)

Brief Answer:
Your test might be showing positive for opioids

Detailed Answer:
Hi XXXXX,
Thanks for writing back with an update.

1. Mersyndol contains codeine which is a prescription drug, and is part of a group of drugs known as opioids. Drug screen tests always give positive result for opioids if consumed before giving test sample.

2. Therefore they have found metabolites of codeine which is part of mersyndol in your test result. It is however difficult to pin point that 2 tablets were taken before the test.

Hope your query is answered.
Do write back if you have any doubts.

Regards,
Dr.Vivek

Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar

Follow up: Dr. Vivek Chail (2 hours later)

Thanks, they didn't confirm the dose was exactly two tablets, but rather it was a 'very low dose' of codeine. They weren't prescription mercyndol, they were over the counter.
I know the obvious answer is to take medication as prescribed but it's complicated. I am just hoping that the 'low dose confirmation' is as close as they are able to get regarding dosage details? Eg. If I consumed 50 diazapam over a course of a 3 days (hypothetical), surely numbers above cut-off would read abnormally high?
Sorry, I think I just asked the same question differently.
Thanks again for your time.

Answered by Dr. Vivek Chail (1 hour later)

Brief Answer:
Please find details below

Detailed Answer:
Hi XXXX,
Thanks for writing back with an update.

1. The screening test by default tells the presence or absence of a drug or group of drugs for which the test is being done.

2. For a drug to show up, it should be present in a minimum quantity to be detectable quantity.

3. Beyond the detectable quantity, the drug will show a positive result whether you consume 5 tablets or 50 tablets over your hypothetical duration of 3 days.

4. The might have confirmed very low dose of codeine enough to trigger the test result as positive.

5. Please do not overdose on these medicines and take them only when required to manage your symptoms like headache and inform the chain of custody so that you come out clean

Hope your query is answered.
Do write back if you have any doubts.

Regards,
Dr.Vivek

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Above answer was peer-reviewed by : Dr. Chakravarthy Mazumdar