Adnkronos (Adnkronos) – Rapid urine tests used to detect fentanyl can, under certain circumstances, yield positive results even when the substance is not present. Possible causes include certain pharmacological therapies, particularly those based on risperidone, a drug used in psychiatry. This is highlighted by a study conducted by researchers at the National Center for Addictions and Doping at the Istituto Superiore di Sanità, published in Clinical Chemistry and Laboratory Medicine.
The authors—the ISS reports—observed that, in some mental health services, several patients tested positive for fentanyl after undergoing rapid urine tests. Something, however, didn't add up: when the same samples were analyzed with more precise laboratory instruments, fentanyl was not detected. Through laboratory analyses capable of identifying numerous substances, the researchers identified two drugs in the samples: risperidone, used to treat certain psychiatric disorders, and valproic acid, used to treat epilepsy and certain mood disorders.
To determine which of the two might be interfering with the tests, the researchers conducted an experiment, adding the drugs separately and then in combination to urine samples that initially contained them. The result was clear: the tests incorrectly flagged the presence of fentanyl when risperidone was present in the urine, even in combination with valproic acid.
The latter, however, did not cause the same effect when present alone.
"The phenomenon is called cross-reactivity, but the concept is simple," explain Manuela Pellegrini and Annagiulia di Trana of the National Center for Addiction and Doping, two of the study's authors. "The test," they clarify, "can confuse one substance with another and report a positive result that, in reality, does not correspond to the presence of fentanyl. A particularly important aspect is that this interference was observed at a concentration of risperidone compatible with that found in the urine of people taking the drug for therapeutic purposes."
"A false positive," says Simona Pichini, director of the National Center for Addictions and Doping at the ISS, "can have serious consequences, especially for someone who regularly takes psychiatric medications. An incorrect result could raise suspicions of drug use, generating concerns and misunderstandings, or influencing healthcare and care decisions. For this reason, a positive rapid test alone should not be considered definitive proof of fentanyl use. When the result is unexpected or could have significant consequences, it is essential to verify it with more specific and reliable laboratory tests."
News
webinfo@adnkronos.com (Web Info)