A Single Sample Method for Estimating Glomerular Filtration Rate in Cats

Abstract

Background: Validated methods of estimating glomerular filtration rate (GFR) in cats requiring only a limited number of samples are desirable.Hypothesis/Objectives: To test a single sample method of determining GFR in cats. Animals: The validation population (group 1) consisted of 89 client-owned cats (73 nonazotemic and 16 azotemic). A separate population of 18 healthy nonazotemic cats (group 2) was used to test the methods.Methods: Glomerular filtration rate was determined in group 1 using corrected slope-intercept iohexol clearance. Single sample clearance was determined using the Jacobsson and modified Jacobsson methods and validated against slope-intercept clearance. Extracellular fluid volume (ECFV) was determined from slope-intercept clearance with correction for the 1 compartment assumption and by deriving a prediction formula for ECFV (ECFV Predicted ) based on the body weight. The optimal single sample method was tested in group 2.Results: A blood sample at 180 minutes and ECFV Predicted were optimal for single sample clearance. Mean AE SD GFR in group 1 determined using the Jacobsson and modified Jacobsson formulae was 1.78 AE 0.70 and 1.65 AE 0.60 mL/min/kg, respectively. When tested in group 2, the Jacobsson method overestimated multisample clearance. The modified Jacobsson method (mean AE SD 2.22 AE 0.34 mL/min/kg) was in agreement with multisample clearance (mean AE SD 2.19 AE 0.34 mL/ min/kg).Conclusions and Clinical Importance: The modified Jacobsson method provides accurate estimation of iohexol clearance in cats, from a single sample collected at 180 minutes postinjection and using a formula based on the body weight to predict ECFV. Further validation of the formula in patients with very high or very low GFR is required.

Relationship between Serum Symmetric Dimethylarginine Concentration and Glomerular Filtration Rate in Cats

“…Ten client‐owned cats were included in this study retrospectively from a group of 89 cats in which GFR had been previously measured and the data published . Cats were selected in order to represent a range of GFR and creatinine values from the group of 89 cats included in the original study.…”

“…Ten client-owned cats were included in this study retrospectively from a group of 89 cats in which GFR had been previously measured and the data published. 6 Cats were selected in order to represent a range of GFR and creatinine values from the group of 89 cats included in the original study. Four of the cats selected had plasma creatinine concentrations above the laboratory reference range, but no concurrent medical disorders were identified based on the recorded history, physical examination or clinicopathologic data, which included routine plasma biochemistry, urinalysis and packed cell volume determination.…”

Chronic urinary bladder torsion causing urinary incontinence in a cat

“…Quantitative scintigraphy has been validated for assessment of GFR in cats and, more recently, a methodology has been established for plasma iohexol and creatinine clearance testing in cats; 11–13 however, GFR was not assessed here. In this cat, however, serum renal biochemical parameters were normal 8 months after surgical correction of the bladder torsion and partial ureteral obstruction.…”

“…15 On this basis a reduced dose rate of iohexol was used (240 mg/kg), which is markedly less than that reported as being used for iohexol tolerance testing (647 mg/kg) in similarly azotaemic cats. 13 …”

Measurement of glomerular filtration rate in cats

“…57 The formula The slope-intercept formula corrects for the missing area under the curve when collecting only a limited number of samples (generally three samples) from the elimination phase of the clearance curve (samples collected at 120, 180 and 240 mins). The uncorrected clearance (GFR uncorrected ), which is standardised to body weight (BW), is inserted into the formula to obtain the corrected clearance, the unit of which is ml/min/kg Single sample GFR is determined from a single sample collected at time t (180 mins) and the volume of distribution of iohexol at time t (Vt) which is calculated as dose of iohexol administered/serum concentration of iohexol at time t. An estimate of ECFV is also required which can be obtained from body weight (kg) using a second formula GFR = glomerular filtration rate; ECFV = extracellular fluid volume Table 2 Formulae for determining GFR using limited sampling plasma clearance methods in cats There is a significant relationship between body weight (BW), extracellular fluid volume (ECFV), body surface area (BSA) and glomerular filtration rate (GFR), and a nonsignificant relationship between GFR standardised to the parameter and GFR, indicating all three methods of standardisation are appropriate in cats.…”