False-Positive Amphetamine Toxicology Screen Results in Three Pregnant Women Using Labetalol

BACKGROUND: Labetalol is commonly used for control of hypertension in pregnancy. A component of the workup for new-onset hypertension in pregnancy often includes a urine drug screen. A labetalol metabolite is structurally similar to amphetamine and methamphetamine, thus causing potential cross-reactivity in drug immunoassays. CASES: We present one case of cocaine-induced hypertensive crisis superimposed on chronic hypertension and two cases of severe preeclampsia for which patients required escalating doses of labetalol for hypertension, with subsequent false-positive amphetamine urine drug screen results. CONCLUSION: In pregnant women requiring labetalol for treatment of hypertensive disease, a urine drug screen may be falsely positive for amphetamines and metham-phetamines. Providers should be cognizant of this possibility when interpreting the results of urine drug screens. (Obstet Gynecol 2011;117:503-6) DOI: 10.1097/AOG.0b013e318206c07c