Lamotrigine and Pheochromocytoma Biochemical Testing

Medication Interference with Catecholamine and Metanephrine Measurements

The Endocrine Society’s clinical practice guideline states that lamotrigine is not listed among medications that cause false‑positive catecholamine or metanephrine results, indicating it does not interfere with these assays. 1
According to the same Endocrine Society guideline, tricyclic antidepressants directly interfere with catecholamine disposition and can produce mild to marked elevations in biochemical test results. 1
The guideline also identifies acetaminophen, mesalamine, and sulfasalazine as analytical interferents that cause false elevations when liquid‑chromatography electrochemical detection (LC‑ECD) methods are used. 1

Proper plasma metanephrine sampling requires 30 minutes of supine rest before blood draw; seated sampling can generate false‑positive results through sympathetic activation. (Praxis Medical Insights) 2
Laboratories should employ LC‑MS/MS or LC‑ECD assays rather than immunoassays, as the former provide more accurate catecholamine and metanephrine measurements regardless of medication use. (Praxis Medical Insights) 2

When a patient on lamotrigine shows elevated metanephrines or catecholamines, the elevation should not be attributed to lamotrigine; clinicians should investigate true pheochromocytoma, inappropriate sampling conditions, physiological stress, or other interfering drugs. (Endocrine Society) 1
Clinicians should review concomitant medications for known interferents such as tricyclic antidepressants, acetaminophen, mesalamine, or sulfasalazine. (Endocrine Society) 1
If initial biochemical results are borderline, repeat testing under optimal conditions (supine positioning, avoidance of interfering substances) before considering a medication effect. (Endocrine Society) 1
Do not discontinue lamotrigine solely on the basis of elevated metanephrines, as no causal relationship has been established. (Endocrine Society) 1
In patients with high clinical suspicion for pheochromocytoma, do not delay imaging work‑up because the patient is taking lamotrigine; proceed with appropriate radiologic evaluation. (Endocrine Society) 1