Ngal elisa assay

IL‐6 (R&D Systems) and IL‐10 (R&D Systems) were measured using ELISA following the manufacturer's instructions. IL‐10 assay was carried out on undiluted perfusate. IL‐6 samples were optimized to fit within the assay standard curve.
Human neutrophil gelatinase‐associated lipocalin (NGAL) ELISA assay (Abcam) was carried out following the manufacturer's instructions. Urine was assayed at 100× dilution.

We used stored serum samples from 12 healthy volunteers and 36 patients with CKD stages 2–5 who participated in previous IRB-approved physiologic studies. All participants provided written informed consent to have their samples stored for future use for analysis of biomarkers related to kidney function and mineral metabolism. We measured NGAL using the NGAL ELISA assay (Abcam, Cambridge, MA, USA). We used a human intact FGF23 (iFGF23) enzyme-linked immunosorbent assay (ELISA) to measure the active iFGF23 protein and a C-terminal FGF23 (cFGF23) ELISA that recognizes the full-length protein and its C-terminal cleavage fragments to measure total FGF23 (both from Immutopics, Carlsbad, CA, USA).