The Klotho gene has been identified as an aging suppressor gene that encodes a 
transmembrane protein, which is expressed primarily in renal tubules. There are 
2 forms of Klotho, membrane and secreted. However, there is a paucity of data on 
levels of soluble Klotho in diseases like diabetes and kidney disease. We 
validated an enzyme-linked immunosorbent assay for Klotho and quantitated Klotho 
levels separately in patients with diabetes and also in patients with chronic 
kidney disease (CKD). The Klotho assay showed good precision and was linear down 
to 19 ng/mL. There were no significant effects on Klotho levels with the 
addition of common interferents such as ascorbate, triglycerides, or hemolysis; 
only bilirubin (250 mg/L) significantly reduced Klotho levels (P < .05). There 
was a significant reduction in Klotho levels in samples with glycated hemoglobin 
(HbA(1c)) levels of 6.5% or more compared with control samples (HbA(1c) < 6.5%; 
P < .001). We also documented significantly higher levels of Klotho with CKD. 
Thus, we validated an assay for Klotho and made the novel observation that 
levels are decreased in diabetes and increased in CKD.