Diagnostic potential of simplified methods for measuring glomerular filtration rate to detect chronic kidney disease in dogs

Background: Glomerular filtration rate (GFR) is the most sensitive indicator of initial renal function decline during chronic kidney disease (CKD), but conventional protocols for measuring GFR are labor-intensive and stressful for the dog. Objectives: To assess the diagnostic potential for detecting CKD with simplified GFR protocols based on iohexol plasma clearance. Animals: Seventeen CKD positive and 23 CKD negative dogs of different breeds and sex. Methods: Prospective nonrandomised study. Plasma iohexol was measured 5, 15, 60, 90, 180 min after injection. GFR was calculated using five samples (GFR5) or simplified protocols based on one, two, or three samples. GFR5 and simplified GFR were compared by Bland-Altmann and concordance correlation coefficient (CCC) analysis, and diagnostic accuracy for CKD by receiver operating characteristic curves. A grey zone for each protocol was bounded by the fourth quartile of the CKD positive population (lower cut-off) and the first quartile of the CKD negative population (upper cut-off). Results: All simplified protocols gave reliable GFR measurements, comparable to reference GFR5 (CCC > 0.92). Simplified protocols which included the 180-min sampling granted the best GFR measure (CCC: 0.98), with strong diagnostic potential for CKD (area under the receiver operating characteristic curve ± SE: 0.98 ± 0.01). A double cut-off including a zone of CKD uncertainty guaranteed reliable diagnosis outside the grey area, and identified borderline dogs inside it. Conclusions: The simplified GFR protocols offer an accurate, hands-on tool for CKD diagnosis in dogs. The grey zone might help decision-making in the management of early kidney dysfunction.