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 nonrandomized study. Plasma iohexol was measured 5, 15, 60, 90, and 180 minutes after injection. Glomerular filtration rate was calculated using 5 samples (GFR5 ) or simplified protocols based on 1, 2, or 3 samples. The 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 gray zone for each protocol was bounded by the fourth quartile of the CKD-positive population (lower cutoff) and the first quartile of the CKD-negative population (upper cutoff). RESULTS: All simplified protocols gave reliable GFR measurements, comparable to reference GFR5 (CCC >0.92). Simplified protocols which included the 180-minutes 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 cutoff including a zone of CKD uncertainty guaranteed reliable diagnosis outside the gray area and identified borderline dogs inside it. CONCLUSIONS: The simplified GFR protocols offer an accurate, hands-on tool for CKD diagnosis in dogs. The gray zone might help decision-making in the management of early kidney dysfunction.