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

Abstract

In Brief 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 methamphetamines. Providers should be cognizant of this possibility when interpreting the results of urine drug screens. Use of labetalol in pregnant women with severe chronic or pregnancy-induced hypertension may result in false-positive urine drug screen results for amphetamines.