Quetiapine-Induced False-Positive Urine Drug Screen Results
Quetiapine can cause false-positive urine immunoassay drug screen results due to cross-reactivity or assay interference. [1–3]
Confirmatory testing with a different analytical method (typically LC-MS/MS or GC-MS) is required to determine whether a positive immunoassay reflects true exposure. [1,3]
Immunoassay Cross-Reactivity Mechanisms
Urine drug screens using immunoassays can yield false positives when non-target medications cross-react with assay antibodies or interfere with detection. [1,3]
Cross-reactivity has been reported across multiple drug classes and assay platforms. [1,3]
Documented False Positives Attributed to Quetiapine
Ketamine immunoassay screens have been reported as false-positive after quetiapine use, with confirmation testing showing negative results for true ketamine exposure. [3]
In one real-world evaluation of methadone immunoassays, quetiapine was identified among medications occurring frequently in cases that were false positive on screening but negative on confirmatory testing. [1]
Quetiapine has also been reported as present in false-positive findings related to other immunoassay panels in toxicology contexts. [2]
Screening vs Confirmatory Testing
Immunoassay positives should be treated as presumptive until confirmatory testing is performed. [1,3]
LC-MS/MS or GC-MS confirmation provides a more specific assessment of the target drug and reduces the likelihood that medication cross-reactivity drives the result. [1,3]
Practical Interpretation of a Positive Result
A new or unexpected positive immunoassay result in a patient taking quetiapine should trigger review of the medication list and prompt confirmatory testing. [1,3]
A history of quetiapine exposure does not prove that the immunoassay result is false positive. [1,3]
Common Clinical Pitfalls
Reliance on screening results alone can lead to misclassification because immunoassays have non-trivial false-positive rates in real-world practice. [1]
False-positive rates vary by assay platform, which can affect concordance with confirmatory testing. [1]
When to Seek Confirmatory Testing
Confirmatory testing is indicated when the immunoassay result is inconsistent with medication history, patient report, or clinical context. [1,3]
Confirmatory testing is especially important when quetiapine is present because published case data and real-world assay evaluations document its association with cross-reactivity. [1,3]
Bottom-Line Clinical Statement
Quetiapine has evidence for causing false-positive urine drug immunoassay results (including ketamine and methadone screening), so immunoassay positives should be confirmed with LC-MS/MS or GC-MS. [1,3]