Determination of optimal sampling times for a two blood sample clearance method using ⁵¹Cr-EDTA in cats

Abstract

Estimation of the glomerular filtration rate (GFR) is a useful tool in the evaluation of kidney function in feline medicine. GFR can be determined by measuring the rate of tracer disappearance from the blood, and although these measurements are generally performed by multi-sampling techniques, simplified methods are more convenient in clinical practice. The optimal times for a simplified sampling strategy with two blood samples (2BS) for GFR measurement in cats using plasma (51)chromium ethylene diamine tetra-acetic acid ((51)Cr-EDTA) clearance were investigated. After intravenous administration of (51)Cr-EDTA, seven blood samples were obtained in 46 cats (19 euthyroid and 27 hyperthyroid cats, none with previously diagnosed chronic kidney disease (CKD)). The plasma clearance was then calculated from the seven point blood kinetics (7BS) and used for comparison to define the optimal sampling strategy by correlating different pairs of time points to the reference method. Mean GFR estimation for the reference method was 3.7+/-2.5 ml/min/kg (mean+/-standard deviation (SD)). Several pairs of sampling times were highly correlated with this reference method (r(2) > or = 0.980), with the best results when the first sample was taken 30 min after tracer injection and the second sample between 198 and 222 min after injection; or with the first sample at 36 min and the second at 234 or 240 min (r(2) for both combinations=0.984). Because of the similarity of GFR values obtained with the 2BS method in comparison to the values obtained with the 7BS reference method, the simplified method may offer an alternative for GFR estimation. Although a wide range of GFR values was found in the included group of cats, the applicability should be confirmed in cats suspected of renal disease and with confirmed CKD. Furthermore, although no indications of age-related effect were found in this study, a possible influence of age should be included in future studies.

Simplified methods for estimating glomerular filtration rate in cats and for detection of cats with low or borderline glomerular filtration rate

“…In other reports concerning simplified methods for GFR estimation, no or only few renal-impaired or hyperfiltrating cats were inclu ded. 5,[7][8][9][10][11]13,14,16 Secondly, all possible time combinations were evaluated. This contrasts with other studies evaluating LSSs with blood sampling on arbitrarily selected time points, often without judging if the selected time points were the most appropriate ones for the GFR method used.…”

“…Multisampling techniques can be stressful or even painful, which limits the practical use, especially in cats. 5 Thus, simplified methods to detect cats with decreased GFR are needed. 6 Several limited sampling strategies (LSSs) have been described to estimate feline GFR, 5,[7][8][9][10][11][12][13][14][15][16] but most of these methods are not sufficiently validated in cats with chronic kidney disease (CKD) to be used in practice.…”

Feline CKD

“…Unfortunately, in most of the studies to date no or only few renally impaired cats were evaluated and none of the methods have been sufficiently validated in cats with CKD to be used in practice. [74][75][76][77][78][79][80][81][82] The authors' group is currently working on limited sampling strategies in cats with a wide range of GFR. 83…”

Effect of background region of interest and time-interval selection on glomerular filtration ratio estimation by percentage dose uptake of 99mTc-DTPA in comparison with 51Cr-EDTA clearance in healthy cats

“…From the injected dose and 2BS, the GFR (expressed in ml/min) could be calculated as follows: 51 Cr-EDTA clearance test The 51 Cr-EDTA plasma clearance test was performed as described previously by one of the authors. 17 Before and after injection of 51 Cr-EDTA, the syringe was weighted on a high precision balance, allowing exact calculation of the injected dose. Two blood samples (1-2 ml) were taken, approximately 36 min (T1) and 240 min (T2) after administration of 51 Cr-EDTA, from the jugular vein.…”

“…2,6 Both 99m Tc-DTPA and 51 Cr-EDTA have been used in cats. 3,7,8,11,13,[15][16][17] Both radiopharmaceuticals are considered as exclusive indicators of the filtration function because they are filtered completely by the glomerulus, are not secreted or reabsorbed by the renal tubules, are not metabolized or produced by the body and are not bound appreciably to plasma protein. 2,10,11,18,19 GFR with 99m Tc-DTPA by dynamic renal scintigraphy is calculated from 99m Tc-DTPA uptake in each kidney using a regression equation that was developed by plotting DTPA uptake data against plasma inulin clearance data.…”