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Method: GC-MS (Gas Chromatography/Mass Spectrometry) measuring organic acid metabolites in urine (CLIA 17D0919496); not cleared or approved by the FDA. Results in mmol/mol creatinine. Not a stand-alone diagnosis; should be interpreted in clinical context.
4-Hydroxyphenyllactic acid comes from tyrosine processing and can also reflect gut bacterial activity, with two possible sources to weigh.
