Does Labetalol Trigger False Positive Drug Testing Results?

Area of Science:

• Pharmacology
• Analytical Chemistry
• Toxicology

Background:

• Labetalol, an alpha- and beta-adrenergic antagonist, is prescribed for hypertension during pregnancy.
• Previous reports suggest labetalol may interfere with drug screening tests, leading to false positives.

Purpose of the Study:

• To investigate the potential of labetalol to cause false-positive results for amphetamines and other drugs.
• To evaluate interference across different specimen types and analytical methods.

Main Methods:

• Labetalol was tested at three concentrations (2.7, 50, 100 μM) in urine, plasma, meconium, and umbilical cord tissue.
• Specimens were analyzed using 41 validated immunoassays and liquid chromatography-tandem mass spectrometry (LC-MS/MS) drug tests.

Main Results:

• Labetalol caused false-positive amphetamine and methamphetamine immunoassay results specifically in meconium specimens.
• No false positives were observed with LC-MS/MS testing for any drug or metabolite across all specimen types.
• Urine, plasma, and umbilical cord tissue did not yield false positives with either method at high labetalol concentrations.

Conclusions:

• Immunoassay drug screening may produce false positives for amphetamines due to labetalol, particularly in meconium.
• Highly specific analytical methods like LC-MS/MS are reliable and do not produce labetalol-induced false positives.