Calcium-phosphorus homeostasis and changes in parathyroid hormone secretion in cats with various stages of spontaneous chronic renal failure

Abstract

Feline chronic renal failure was recognized with increased frequency in Maine coon, Abyssinian, Siamese, Russian blue, and Burmese cats. The objective of this study was to investigate the relationship between parathyroid hormone (PTH) level, calcium, and phosphorus homeostasis and the development of various stages of the naturally occurring chronic renal failure (CRF) in cats. Thirty-two CRF cats without history of receiving special diet for renal diseases that were presented to the Small Animal Hospital, Faculty of Veterinary Science, Chulalongkorn University were studied. Nineteen CRF cats were followed prospectively for 60 days and divided into two groups: uremic group (11 cats) and end-stage group (eight cats). The control group (13 cats) were normal cats, which were brought for vaccination at the same hospital within the same period. CRF cats with blood urea nitrogen concentrations of more than 50 mg/dl, serum creatinine level of more than 2.1 mg/dl, and urine specific gravity of between 1.008 and 1.014 were included into the study. Completed blood count, blood chemistry, electrolytes, including sodium, potassium, total calcium, and phosphorus, and PTH levels were measured on days 0, 14, 30, and 60 after the first diagnosis. The results showed that cats with CRF had significantly lower red blood cells, hemoglobin, and pack cell volume than control cats (p < 0.01) on days 0, 14, 30, and 60. PTH levels on first day of diagnosis were 50.51 ± 19.65, 79.41 ± 28.12, and 183.37 ± 50.12 pg/ml in controls, uremic, and end-stage groups, respectively. Cats in end-stage group had significantly increased levels of PTH when compared to control (p < 0.01) and uremic groups (p < 0.05) on days 0, 14, and 30. Serum phosphorus levels also increased significantly in end-stage group (p < 0.001), indicating the presence of renal secondary hyperparathyroidism. This study reveals that PTH level is significantly increased in end-stage CRF cats who did not received special diet for renal diseases. The development of renal secondary hyperparathyroidism in end-stage CRF cats significantly decreased its survival rate.