OBJECTIVE: Soluble serum Klotho, is a new biomarker linked to chronic kidney disease, cardiovascular disease and diabetes. This study describes the evaluation and comparison of two different immunoassays and establishment of assay specific reference intervals in adults. Design and methods Serum Klotho concentrations were determined in 120 healthy adults aged 19-66years. Blood samples were collected, and stored sera were assayed for Klotho according to age and gender. In addition several other clinical and laboratory characteristics were determined in the cohort and compared to the levels of serum Klotho. RESULTS: Serum Klotho levels were significantly higher in time-resolved fluorescence immunoassay (TRF) compared to an ELISA (IBL) and no correlation were found between the assays. No signal was obtained in either assay when the standard curve was switched between the two different immunoassays. The median serum Klotho concentration using TRF was 61ng/mL (2.5-97.5% reference limits; 11-181ng/mL) for males and 99ng/mL (2.5-97.5% reference limits; 19-316ng/mL) for females while the ELISA gave a mean value of 472pg/mL (2.5-97.5% reference limits; 204-741pg/mL) with no difference between genders. Concentrations of serum Klotho were independently associated with estimated glomerular filtration rate (eGFR) and body weight using TRF whereas serum Klotho concentrations were associated with age using the ELISA. CONCLUSION: Comparison of two different immunoassays for serum Klotho indicate, that the protein exists in human beings in different forms which may function as independent factors and whose role and potential value as biomarkers needs to be evaluated separately. Reference intervals specific for the different forms recognised by the different assays were calculated in this study.
Clinical Biochemistry, 2013, Vol 46, Issue 12, p. 1079-1083