Direct LC-MS/MS and indirect GC-MS/MS methods for measuring urinary bisphenol A concentrations are comparable

Area of Science:

• Environmental Health
• Analytical Chemistry
• Biomonitoring

Background:

• Bisphenol A (BPA) is commonly measured in urine via indirect methods involving enzymatic deconjugation and extraction.
• Direct methods measure free and conjugated BPA simultaneously, summing them for total urinary BPA.
• Accurate interpretation of biomonitoring data for risk assessment necessitates statistical comparison between direct and indirect BPA measurement methods.

Purpose of the Study:

• To compare urinary BPA concentrations obtained from direct and indirect measurement methods.
• To analyze duplicate first-trimester urine samples from 1879 pregnant women in the MIREC Study.

Main Methods:

• Urinary BPA concentrations were measured using gas chromatography-tandem mass spectrometry (GC-MS/MS) for the indirect method.
• Free and conjugated BPA were summed for the direct method, measured via liquid chromatography-tandem mass spectrometry (LC-MS/MS).
• Bland-Altman analysis was employed to evaluate method deviations, stratified by urine specific gravity and limit of quantification (LOQ).

Main Results:

• Median urinary BPA concentrations were 0.89 µg/L (direct) and 0.81 µg/L (indirect).
• The direct method yielded results 8.6% higher on average than the indirect method.
• Percent differences varied significantly with urine specific gravity (4.0% for <1.02 vs. 20.3% for ≥1.02) and showed wider agreement limits below the LOQ.

Conclusions:

• This study, the largest comparison of direct and indirect BPA methods, found the direct method yields higher BPA concentrations.
• Findings contrast with previous research suggesting indirect methods underestimate total BPA exposure.
• Observed differences between methods are unlikely to alter health outcome data interpretation in risk assessments.