Blood Urea Nitrogen Levels to Verify Estimated Glomerular Filtration Rate, as Derived from 2 Commonly Used Equations

BACKGROUND: A blood urea nitrogen to creatinine ratio (BCR) of 20 or greater indicates various physiological conditions. Whether glomerular filtration rate (GFR) estimates obtained using the Modification of Diet in Renal Disease (MDRD) study equation and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) study equations are affected by a high BCR remains unknown. METHODS: Patients who underwent urine creatinine clearance (CrCl) and serum blood urea nitrogen (BUN) and creatinine assessments on the same day were enrolled in our study. Those with BCR of 20 or greater and less than 20 were categorized into high- and low-BCR groups. The concordance on diagnosing chronic kidney disease (CKD) stages by using urine CrCl level and serum GFR estimates was assessed. RESULTS: More disagreement in CKD stage diagnosis was observed in the high-BCR group (weighted κ = 0.600 and 0.541 for the MDRD and CKD-EPI study equations, respectively) than in the low-BCR group (weighted κ = 0.816 and 0.758, respectively). CONCLUSIONS: A BCR of 20 or greater caused misestimation of the CKD stage. GFR estimates for patients with high BCR should be interpreted cautiously.