Estimation of glomerular filtration rate by plasma clearance of iohexol in healthy horses of various ages.

Abstract

BACKGROUND: Plasma clearance of iohexol is a reliable method to assess the glomerular filtration rate (GFR). The relationship between aging and GFR in horses is unclear. HYPOTHESIS/OBJECTIVES: To compare GFR estimated by iohexol clearance in horses of different ages. ANIMALS: Twenty-one clinically healthy horses were enrolled. METHODS: Prospective study. Groups: (A) composed by 8 young horses (&#x2264;14&#x2009;years old) with serum creatinine <1.5 mg/dL, (B) by 7 aged horses (&#x2265;20&#x2009;years old) with serum creatinine <1.5 mg/dL, and (C) by 6 aged horses (&#x2265;20&#x2009;years old) with serum creatinine &#x2265;1.5 mg/dL. Iohexol was injected (75.5 mg/kg) through an IV catheter, and plasma samples were collected 5, 30, and 90&#x2009;minutes later. Plasma clearance of iohexol was obtained by the high-performance liquid chromatography-ultraviolet method. RESULTS: The GFR was 2.6, 2.1, and 1.45&#x2009;mL/min/kg (median value) in Groups A, B, and C, respectively. Statistical analysis showed differences between Group A versus B and A versus C for urea, and A versus C for creatinine and GFR. CONCLUSIONS AND CLINICAL IMPORTANCE: Glomerular filtration rate was significantly reduced in aged horses with serum creatinine &#x2265;1.5 mg/dL compared to young horses with creatinine <1.5 mg/dL; no differences were obtained between young and aged horses with creatinine <1.5 mg/dL. Glomerular filtration rate evaluation should be considered in aged horses even if the plasma creatinine values are normal.