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Dr. Andrew Rynne
MD
Dr. Andrew Rynne

Family Physician

Exp 50 years

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What Causes False Negative Test Report For Fentanyl Patch?

Hello, My name is Quyen Nguyen. Here is my question. I had Chronic pain for the last 15 or more years. The pass 7 years, the Doctor had precised the Fetanyl patch 50mg for me and I wear the patch ever since for the pass 7 years, for every hour and every day. Last month, the company required I give the urine for test, after 3 times of test they told me that I didn t used or wear the patch, because the Fentanyl drug didn t show or show negative in my urine test. What should I do to prove to them that I had used the patch or they will stop to prescribed the patch for me again? Thank you.
Sun, 27 May 2018
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General & Family Physician,  's  Response
Hello and Welcome to ‘Ask A Doctor’ service.
I have reviewed your query and here is my advice.


I have read your question and understand your concern.

My answer is as follows:

Generally, drug tests are designed in order to have a very high (almost 100%) specificity, meaning that they are able to correctly produce a negative result when indeed no drug is present in the specimen (high true negative rate of the test).

However, there are many factors which could enhance the false-negative rate of a drug test. These include changes of urine specimens (over diluting, enhancing or substituting it), and use of very high cut-off levels. In the later case, even if the drug is present in urine the test will result negative because the cut-off level (set very high) has not been reached.

A recent study in Canada has suggested that fentanyl test strips could produce a unusually high false-negative result!

If you have done previously the urine drug test and the test showed positive (the same test that was used recently) and with everything else being equal (same lifestyle patterns, regular use of the patch, same hydration level, etc.) then there is no reason for the test to behave differently.

If any of the above has changed, then you and the company should look in more detail your situation in order to find the cause of a negative test result. The company can order more specific (yet more expensive) laboratory tests in order to verify whether there is some traces of fentanyl in urine.

You can also ask the company what was the cut-off value of the test used.

What can you do to improve the chances of drug detection in your urine, is to drink less water on the previous and test-day in order for the urine to be more concentrated. This will improve the test ability to detect the drug.



I wish you the best of luck!
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What Causes False Negative Test Report For Fentanyl Patch?

Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. I have read your question and understand your concern. My answer is as follows: Generally, drug tests are designed in order to have a very high (almost 100%) specificity, meaning that they are able to correctly produce a negative result when indeed no drug is present in the specimen (high true negative rate of the test). However, there are many factors which could enhance the false-negative rate of a drug test. These include changes of urine specimens (over diluting, enhancing or substituting it), and use of very high cut-off levels. In the later case, even if the drug is present in urine the test will result negative because the cut-off level (set very high) has not been reached. A recent study in Canada has suggested that fentanyl test strips could produce a unusually high false-negative result! If you have done previously the urine drug test and the test showed positive (the same test that was used recently) and with everything else being equal (same lifestyle patterns, regular use of the patch, same hydration level, etc.) then there is no reason for the test to behave differently. If any of the above has changed, then you and the company should look in more detail your situation in order to find the cause of a negative test result. The company can order more specific (yet more expensive) laboratory tests in order to verify whether there is some traces of fentanyl in urine. You can also ask the company what was the cut-off value of the test used. What can you do to improve the chances of drug detection in your urine, is to drink less water on the previous and test-day in order for the urine to be more concentrated. This will improve the test ability to detect the drug. I wish you the best of luck!