Recently, focus has been on developing tests to diagnose chronic kidney disease (CKD) or complications earlier, therefore, diminishing secondary conditions and extending quality of life. Chronic kidney disease is quite prevalent as cats age, 31% of cats over 15 years of age have azotemic CKD and the prevalence of CKD in this aged group of cats is 80.9%.
One syndrome with abnormalities correlated with CKD and renal osteodystrophy is called chronic kidney disease-mineral and bone disorders (CKD-MBD). Development of this syndrome is a consequence of reduced glomerular filtration rate (GFR) and associated phosphate retention. Calcium-phosphate derangements are prevalent in cats with CKD, the most common being hyperparathyroidism (in 84% of azotemic cats).
Fibroblast growth factor-23 (FGF-23) and parathyroid hormone (PTH) have been found to be commonly elevated in cats with azotemic CKD. FGF-23 is secreted in response to hyperphosphatemia and increased plasma calcitriol concentrations. Both concentrations (FGF-23 and PTH) are utilized in human patients as predictors of survival times. This relationship has not been studied in the cat. This retrospective study evaluated 241 azotemic, client-owned cats by investigating plasma FGF-23 and PTH concentrations at the time of diagnosis of CKD following survival time and disease progression over a 12-month period.
In comparing the results, survival time was decreased (negatively associated) with plasma creatinine and FGF-23 concentrations, urine protein-creatinine ratios and age. Survival was positively associated with PCV (normal values and not decreasing). Neither plasma phosphate nor PTH were found to be an independent predictor of survival time or progression of the disease. The development of CKD-MBD syndrome is believed to cause damage to kidney tissue and add to disease progression.
Plasma FGF-23 is noted to increase early in the development of CKD, before obvious evidence of hyperphosphatemia. It is not known if FGF-23 is a uremic toxin or more a surrogate marker for other causes of uremic toxicity. Feeding a phosphate-restricted diet in CKD patients has been shown to reduce plasma FGF-23 concentrations. Additional research will need to be performed to demonstrate whether a targeted reduction in FGF-23 may improve survival time. A finding of increased FGF-23 might make it a useful biomarker for predicting a poorer prognosis in cats with CKD. More still needs to be determined if FGF-23 is a mediator, or a marker of CKD-MBD in cats. (VLT)
Finch NC, Geddes RF, et al. Fibroblast growth factor 23 (FGF-we) concentrations in cats with early nonazotemic chronic kidney disease (CKD) and in healthy geriatric cats. J Vet Intern Med. 2013 Mar-Apr;27(2):227-233.