A portable fiberoptic ratiometric fluorescence analyzer provides rapid point-of-care determination of glomerular filtration rate in large animals

Abstract

Measurement of the glomerular filtration rate (GFR) is the gold standard for precise assessment of kidney function. A rapid, point-of-care determination of the GFR may provide advantages in the clinical setting over currently available assays. Here we demonstrate a proof of principle for such an approach in a pig and dogs, two species that approximate the vascular access and GFR results expected in humans. In both animal models, a sub-millimeter optical fiber that delivered excitation light and collected fluorescent emissions was inserted into a peripheral vein (dog) or central venous access (pig) by means of commercial intravenous catheters. A mixture of fluorescent chimeras of a small freely filterable reporter and large non-filterable plasma volume marker were infused as a bolus, excited by light-emitting diodes, and the in vivo signals detected and quantified by photomultiplier tubes in both species in less than 60 min. Concurrent standardized 6-h iohexol plasma kidney clearances validated the accuracy of our results for both physiologic and a chronic kidney disease setting. Thus, our ratiometric technique allows for both measurement of plasma vascular volume and highly accurate real-time GFR determinations, enabling clinical decision making in real time.

Figures

Figure 1. Design of the ratiometric optical fiber system

(a) Optical layout. 1a and 1b, light-emitting diodes (LED) power supplies; 2a and 2b, amber and blue LEDs, respectively; 3a and 3b, collimating condensers with apertures; 4a and 4b, excitation bandpass filters; 5, excitation dichroic mirror; 6, dual-band dichroic mirror; 7, fiber lens with aperture; 8, fiber adapter; 9, optical fiber; 10, catheter; 11, emission dichroic mirror; 12a and 12 b, photomultiplier tube (PMT) focus lenses with apertures; 13a and 13b, emission filters; 14a and 14b, PMTs. (b) Cross-section showing optical components. (c) Electronic system of the device. SPI, serial peripheral interface.

Figure 2. Quantifying plasma volume and glomerular filtration rate in a pig using fluorescent inulin and dextran

Time courses for the reporter 5 kDa fluorescein isothiocyanate-inulin and the marker 150 kDa Texas Red dextran after a co-injection into an Osabaw swine. The fluorescence ratio (inulin/dextran) data (dots) were fitted to a bi-exponential equation and the fitted curve is shown as a solid line. The original data that generated the ratio are shown in inset.

Figure 3. Quantifying plasma volume and glomerular filtration rate in dogs using fluorescent dextrans

The data shown in a and b were generated from a dog under physiological conditions and a chronic kidney disease model, respectively. The 5/150 kDa ratio data (dots) from the optical device were fit to a bi-exponential equation. In each case, the fitted curve is shown as a solid line. A good overlap is seen between the device data points and the plasma fluorescence of the 5 kDa fluorescein isothiocyanate-dextran (triangles) from a spectroscopic analysis. The original data that generated the ratio are shown in the inset in each panel.