Laboratory aspects of circulating α-Klotho.

BACKGROUND α-Klotho is a protein mainly produced in the kidney. Its circulating form has been suggested to link renal damage and distant tissue pathology. As three assays to measure α-Klotho became commercially available, we performed an evaluation of these commercially available Klotho assays. METHODS We studied within-run variation, between-run variation, matrix effects, linearity, and recovery of added recombinant human Klotho in the α-Klotho assays of IBL (IBL International GmbH, Hamburg, Germany), Cusabio (Cusabio Biotech, Wuhan, China) and USCN (USCN life Science, Inc., Wuhan, China) using both serum and ethylenediaminetetraacetic acid plasma. RESULTS Within run variation was 4, 13 and 32% for the IBL, Cusabio and USCN assay, respectively. Agreement between serum and EDTA plasma was good in the IBL assay, but poor in the USCN and Cusabio assays however improved after modifications in the Cusabio assay. Standardization and agreement between assays was poor. CONCLUSIONS The commercially available methods for the measurement of α-Klotho differ in quality. Some of the manufacturers should improve their assays in order to produce accurate results so that reliable conclusions can be drawn from studies in which these assays are used.