From the Guidelines
A false positive Tricyclic Antidepressant (TCA) on a urine drug screen does not necessarily indicate the presence of TCAs, but rather may be due to cross-reactivity with other substances [ 1 ].
Possible Causes of False Positives
- Certain medications, such as fluoroquinolone antibiotics, can cause false positive results due to cross-reactivity with the immunoassay screen [ 1 ]
- Prescription medications, such as amphetamine and dextroamphetamine, can also lead to false positive results [ 1 ]
- Other substances, including foods or over-the-counter medications, may metabolize into compounds that are detected by the drug testing panel, resulting in a false positive [ 1 ]
Next Steps
To accurately interpret the results, it is essential to:
- Confirm the result with a more specific test, such as gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS)
- Review the patient's medication list and medical history to identify any potential causes of the false positive result [ 1 ]
- Consider repeat urine testing to confirm the results, if necessary By taking these steps, healthcare providers can ensure accurate interpretation of urine drug screen results and avoid potential misdiagnosis or mismanagement of patients [ 1 ].
From the Research
False Positive Tricyclic Antidepressant (TCA) Results
A false positive Tricyclic Antidepressant (TCA) result on a urine drug screen can indicate the presence of other substances that cross-react with the TCA assay. Some of these substances include:
- Diphenhydramine, an antihistamine medication, which can cause false positive results for TCAs in urine examination 2, 3
- Carbamazepine, an anticonvulsant medication, which can cause false positive tricyclic antidepressant drug screen results 4
- Certain antipsychotic medications, antihistamines, and the muscle relaxant cyclobenzaprine, which can also cause false positive tricyclic antidepressant toxic screen results 4
- Phenothiazines and other medications, which can interfere with TCA assays and cause false positive results 5
Cross-Reactivity and Interference
The cross-reactivity and interference of these substances with TCA assays can lead to false positive results, which can confound the identification of ingested toxins. It is essential to consider the possibility of cross-reactivity in the diagnosis of patients with unknown acute drug intoxication who test positive for TCAs 2, 3, 4. Verification of samples using more specific methods, such as gas chromatography/mass spectrometry, is necessary to confirm the presence of TCAs or other substances 6, 5.