A pilot study to assess the feasibility of transcutaneous glomerular filtration rate measurement using fluorescence-labelled sinistrin in dogs and cats

In dogs and cats an assessment of renal function is often needed, however, existing methods including urine and plasma clearances are invasive, cumbersome and time consuming. This pilot study evaluated the feasibility of a transcutaneous glomerular filtration rate (GFR) measurement in dogs and cats. Additionally the optimal dose and location for the transcutaneous measurement device were investigated. Renal elimination of fluorescein-isothiocyanate-labelled sinistrin (FITC-S) was measured transcutaneously for 4 hours. The procedures were performed in awake, freely moving animals using escalating doses of FITC-S (10 mg/kg, 30 mg/kg, 50 mg/kg) with a wash-out period of at least 24 h in between. Multiple devices were placed on each animal. The resulting FITC-S disappearance curves were visually assessed to determine the most suitable location and the appropriate dose to reach an adequate transcutaneous peak signal for kinetic analysis. In both species 30 mg/kg were adequate for kinetic calculation. The most suitable place for the device was the lateral thoracic wall in dogs and the ventral abdominal wall in cats, respectively. Transcutaneous FITC-S clearance was then repeated using the optimal dose and location and in parallel with an additional plasma sinistrin clearance. Plasma elimination half-lives [min] were 26, 31 and 35, and corresponding transcutaneous elimination half-lives [min] were 26, 34 and 55, respectively in the dogs. Plasma elimination half-lives [min] were 51, 60 and 61, and corresponding transcutaneous elimination half-lives [min] were 75, 96 and 83, respectively in the cats. In conclusion, transcutaneous FITC-S clearance is a feasible method for the assessment of GFR in awake dogs and cats. It is noninvasive, well tolerated and easy to perform even in a clinical setting with results being readily available. A dose of 30 mg/kg of FITC-S seems adequate for kinetic assessment. Further studies are now needed to establish reference values and evaluate transcutaneous renal clearance in various conditions

Transcutaneous disappearance curves of fluorescein-isothiocyanate-labelled sinistrin in three dogs (A–C) and three cats (D–F) using a dose of 30 mg/kg.

<p>Transcutaneous disappearance curves of fluorescein-isothiocyanate-labelled sinistrin in three dogs (A–C) and three cats (D–F) using a dose of 30 mg/kg.</p

Transcutaneous disappearance curves of fluorescein-isothiocyanate-labelled sinistrin in a dog with the device placed on the four different locations (A – hindlimb, B – forelimb, C – ventral abdomen, D – lateral thorax).

<p>The x-axis represents time, the y-axis represents the relative transcutaneous fluorescence. Note that there are minimal artifacts in curve D.</p

Transcutaneous disappearance curves of a cat using three different dosages of fluorescein-isothiocyanate-labelled sinistrin (A: 10 mg/kg, B: 30 mg/kg, C: 50 mg/kg).

<p>The x-axis represents time, the y-axis represents the relative transcutaneous fluorescence. The dose of 30 mg/kg (B) results in an adequate peak concentration.</p

Plasma inulin data in all animals studied.

<p>Plasma inulin data in all animals studied.</p

Results of serum sinistrin and transcutaneous fluorescein-isothiocyanate-labelled sinistrin clearance in all animals studied.

<p>(<i>FITC-S = fluorescein-isothiocyanate-labelled sinistrin, k = transfer rate between compartments, Vss = Volume of distribution under steady state conditions</i>).</p><p>Results of serum sinistrin and transcutaneous fluorescein-isothiocyanate-labelled sinistrin clearance in all animals studied.</p

The miniaturized device is placed on a clipped area on the ventral abdomen of a beagle dog and attached using a sticky patch.

<p>The miniaturized device is placed on a clipped area on the ventral abdomen of a beagle dog and attached using a sticky patch.</p