Establishing a Reference Interval for Fibroblast Growth Factor (FGF)-23 in Cats

Fibroblast growth factor (FGF)-23 is a phosphaturic hormone. An association between increasing FGF-23 levels and progression of chronic kidney disease (CKD) was documented in cats, dogs, and humans. The information regarding reference intervals (RIs) of FGF-23 in cats is limited. We aimed to establish RIs in a large cohort of clinically healthy cats and to investigate correlations with sex and age. A total of 118 cats with unremarkable complete blood count and serum chemistry profile were included. Clinically sick cats, cats with concurrent diseases, suspicion of CKD, or receiving renal diets were excluded. FGF-23 concentrations were measured with the FGF-23 ELISA Kit. RIs were calculated using the reference interval advisor software 2.1 (Microsoft Excel). FGF-23 concentrations were correlated with sex and age. The RI for FGF-23 concentrations spanned 85.8 to 387.0 pg/mL (90% confidence interval: lower limit 40.5 to 103.9 pg/mL, upper limit: 354.6 to 425.0 pg/mL). No significant relationships (r2 = 0.044) were detected with age (p = 0.081) or sex (p = 0.191). Other studies of the same diagnostic assay calculated RIs of 56 to 700 pg/mL in 79 cats and < 336 pg/mL in 108 cats, and in concordance with the present study, did not detect any correlation with sex or age.