Validation of a metabolite panel for a more accurate estimation of glomerular filtration rate using quantitative LC-MS/MS

BACKGROUND: Clinical practice guidelines recommend estimation of glomerular filtration rate (eGFR) using validated equations based on serum creatinine (eGFRcr), cystatin C (eGFRcys), or both (eGFRcr-cys). However, when compared with the measured GFR (mGFR), only eGFRcr-cys meets recommended performance standards. Our goal was to develop a more accurate eGFR method using a panel of metabolites without creatinine, cystatin C, or demographic variables. METHODS: An ultra-performance liquid chromatography–tandem mass spectrometry assay for acetylthreonine, phenylacetylglutamine, pseudouridine, and tryptophan was developed, and a 20-day, multiinstrument analytical validation was conducted. The assay was tested in 2424 participants with mGFR data from 4 independent research studies. A new GFR equation (eGFRmet) was developed in a random subset (n 1615) and evaluated in the remaining participants (n 809). Performance was assessed as the frequency of large errors [estimates that differed from mGFR by at least 30% (1 P ₃₀ ); goal 10%]. RESULTS: The assay had a mean imprecision (10% intraassay, 6.9% interassay), linearity over the quantitative range (r ² 0.98), and analyte recovery (98.5%–113%). There was no carryover, no interferences observed, and analyte stability was established. In addition, 1 P ₃₀ in the validation set for eGFRmet (10.0%) was more accurate than eGFRcr (13.1%) and eGFRcys (12.0%) but not eGFRcr-cys (8.7%). Combining metabolites, creatinine, cystatin C, and demographics led to the most accurate equation (7.0%). Neither equation had substantial variation among population subgroups. CONCLUSIONS: The new eGFRmet equation could serve as a confirmatory test for GFR estimation.