ORIGINAL ARTICLE Calcium–phosphorus homeostasis in cats with spontaneous chronic kidney disease and metabolic acidosis Rosama Pusoonthornthum & Onrassamee Vimuktanandana & Pinit Pusoonthornthum & Anudep Rungsipipat & Nateetip Krishnamra Received: 15 December 2010 / Accepted: 9 February 2011 # Springer-Verlag London Limited 2011 Abstract The effect of metabolic acidosis on calcium– phosphorus homeostasis in cats with spontaneous chronic kidney disease (CKD) was studied. The cats were assigned into the clinically normal cats (n =6), CKD (n =9), and CKD with metabolic acidosis (12 cats). The CKD cats were cats with a blood urea nitrogen ≥50 mg/dl and creatinine level ≥2.1 mg/dl. A complete blood count, sodium, potassium, total calcium, adjusted calcium, ionized calcium, phosphorus, parathyroid hormone, and vitamin D levels were measured. The cats with spontaneous CKD had a significantly lower hemoglobin and pack cell volume than the clinically normal cats. The CKD cats with metabolic acidosis had mean creatinine levels of 7.12±0.76 mg/dl (severe azotemic stage) and significant- ly increased levels of parathyroid hormone and plasma phosphorus levels which indicated the presence of renal secondary hyperparathyroidism. Keywords Metabolic acidosis . Chronic kidney disease . Cats Abbreviations CKD Chronic kidney disease CRF Chronic renal failure IRIS International Renal Interest Society Introduction Chronic kidney disease (CKD) is a common renal disease that affects the geriatric cats. CKD is defined as primary renal failure that has persisted for months to years (Fine et al. 1998). In the USA, the prevalence of feline kidney disease ranged between 1.6% in general cat population (Lund et al. 1999) and 20% in cats presented to the veterinary hospitals in Australia (Watson 2001). In 2000, the prevalence was 96 cases for every 1,000 cats examined in the veterinary teaching hospitals in the USA (Veterinary Medical Data Base, Purdue University, USA). The prevalence of renal failure among cats of 10 years of age or older was 77 cats per 1,000 cats examined, and among cats older than 15 years, 153 cases per 1,000 cats examined (Lulich et al. 1992). Metabolic acidosis is a common complication of CKD in cats, affecting 60% to 80% of patients (Lulich et al. 1992; DiBartola et al. 1987). In one retrospective study of cats with renal failure, 80% of the CKD cats had metabolic acidosis (Lulich et al. 1992). Studies in rats have demonstrated that chronic metabolic acidosis leads to renal damage and progressive loss of functioning nephrons (Nath et al. 1985; Tolins et al. 1987). One report has suggested that metabolic acidosis may accompany cats in an advanced stage of chronic renal failure (Elliot et al. 2003a, b). The objective of this study was to investigate the effects of acute metabolic acidosis on calcium–phosphorus homeostasis in cats with spontaneous chronic kidney disease. R. Pusoonthornthum (*) : O. Vimuktanandana : P. Pusoonthornthum Department of Veterinary Medicine, Faculty of Veterinary Science, Chulalongkorn University, Bangkok 10330, Thailand e-mail: trosama71@hotmail.com A. Rungsipipat Department of Veterinary Pathology, Faculty of Veterinary Science, Chulalongkorn University, Bangkok 10330, Thailand N. Krishnamra Department of Physiology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand Comp Clin Pathol DOI 10.1007/s00580-011-1213-8