Is a prescription medication (prescribed by a physician) obtained in a foreign country a valid explanation for a positive urine drug test result?

From the Guidelines

A prescription medication obtained in a foreign country can be a valid explanation for a positive urine drug test result, but only with proper documentation and verification. This is because many medications available internationally contain substances that are controlled or prohibited in other countries, such as codeine-containing products, tramadol, or certain benzodiazepines 1. When interpreting drug test results, it is essential to consider the individual's complete medical history, including prescribed medications, as drug testing cannot distinguish between appropriate use and misuse of prescribed medications 1.

Some key points to consider when evaluating a positive urine drug test result due to foreign medication include:

• The need for proper documentation, including the medication name, dosage, prescribing physician information, and pharmacy details
• The importance of Medical Review Officer (MRO) verification of any prescription medication, regardless of where it was prescribed
• The potential for cross-reactivity with unrelated substances in the urine, which can lead to false-positive results 1
• The variation in drug testing standards and medication regulations between countries, which can lead to confusion and misinterpretation of test results

To avoid such situations, it is recommended that individuals:

• Research medication regulations before traveling internationally
• Declare all medications when crossing borders
• Keep medications in original packaging
• Carry a letter from the prescribing physician explaining the medical necessity By taking these steps, individuals can ensure that their prescription medication is properly documented and verified, and that any positive urine drug test result is accurately interpreted in the context of their medical history and medication use 1.

From the Research

Validity of Prescription Medication as an Explanation for Positive Urine Drug Test Results

• A prescription medication obtained in a foreign country can be a valid explanation for a positive urine drug test result, as certain medications can cause false-positive results 2.
• However, it is essential to consider the specific medication, its metabolites, and the testing method used to determine the validity of this explanation 3, 4.
• Studies have shown that various prescription medications, such as antihistamines, antidepressants, and antibiotics, can interfere with urine drug screens and produce false-positive results 5, 2.

Factors Affecting Urine Drug Test Results

• The cutoff levels used in urine drug testing can significantly impact the results, and methods using high cutoffs may yield false-negative results 6.
• The use of high-sensitivity analytical methods, such as liquid chromatography tandem mass spectrometry (LC-MS/MS), can reduce false-negative results and provide more accurate test results 6.
• Electronic health record (EHR) data can be used to identify medications that may cause false positives on point-of-care urine drug screening assays 5.

Importance of Confirmatory Testing

• Immunoassay positive results are considered presumptive until confirmed by a second independent chemical technique, such as gas chromatography-mass spectrometry 4, 2.
• Confirmatory testing is crucial to avoid adverse consequences for patients, as false-positive results can have significant implications 3, 2.