Study Objective To evaluate the accuracy of four equations based on serum creatinine concentration—the original Schwartz equation and the Leger, Bedside Chronic Kidney Disease in Children (CKiD), and Counahan-Barratt equations—for determining glomerular filtration rate (GFR) in pediatric patients with chronic kidney disease. Design Retrospective, observational, cross-sectional study. Setting Single-center, academic, outpatient pediatric nephrology clinic. Patients Fifty-three pediatric patients with stages 2–5 chronic kidney disease who completed GFR assessment with 125I-iothalamate between January 2002 and January 2005. Measurement and Main Results Data were collected from each patient’s medical record. Glomerular filtration rate data were analyzed using 59 evaluations from the 53 pediatric patients. 125I-iothalamate clearance was used as the index GFR. The Bedside CKiD and Counahan-Barratt equations outperformed the Schwartz and Leger equations when the index GFR was less than 60 ml/minute/1.73 m2; the Schwartz and Counahan-Barratt equations performed best for index GFRs of 60 ml/minute/1.73 m2 or greater. Overestimation was highest with the Schwartz and Leger equations (> 20% index GFR in 57.6% and 62.7% of patients, respectively). Underestimation was highest with the Bedside CKiD and Counahan-Barratt equations (> 20% index GFR in 30.5% and 28.8%, respectively). Conclusion The new Bedside CKiD equation performed well for pediatric patients with moderate-to-severe chronic kidney disease, but less well for pediatric patients with mild disease. Additional studies are needed to develop more precise GFR equations using serum creatinine concentration.

BackgroundMonitoring urine protein:creatinine ratios (UPC) in dogs with protein‐losing nephropathy (PLN) is challenging because of day‐to‐day variation in UPC results.Hypothesis/ObjectivesDetermine whether single, averaged, or pooled samples from PLN dogs receiving medical treatment yield comparable UPCs, regardless of degree of proteinuria.AnimalsTwenty‐five client‐owned PLN dogs receiving medical treatment.Methods UPC ratios were prospectively measured in each dog utilizing 3 methods: single in‐hospital sample (day 3), average sample (days 1–3), and pooled sample (equal pooling of urine from days 1–3). Bland‐Altman analysis was performed to evaluate agreement between methods for all dogs, as well as in subgroups of dogs (UPC ≤4 or UPC >4).ResultsFor all dogs, Bland‐Altman log‐transformed 95% limits of agreement were −0.07–0.18 (single versus pooled UPC), −0.06–0.16 (single versus average UPC), and −0.06–0.04 (pooled versus average UPC). For dogs with UPC ≤4, Bland‐Altman 95% limits of agreement were −0.42–0.82 (single versus pooled UPC), −0.38–0.76 (single versus average UPC), and −0.27–0.25 (pooled versus average UPC). For dogs with UPC >4, Bland‐Altman 95% limits of agreement were −0.17–2.4 (single versus pooled UPC), −0.40–2.2 (single versus average UPC), and −0.85–0.43 (pooled versus average UPC).Conclusions and Clinical Importance UPC ratios from all methods were comparable in PLN dogs receiving medical treatment. In PLN dogs with UPC >4, more variability between methods exists likely because of higher in‐hospital results, but whether this finding is clinically relevant is unknown.