BUN/Creatinine ratio as a predictor of Tubulointerstitial Nephritis

Abstract

Introduction: Acute interstitial nephritis (AIN) is one of the leading causes of acute kidney injury in hospitalized patients, occurring in 15% to 27% of kidney biopsies performed in patients with AKI. The blood urea nitrogen-to-creatinine ratio (BCR) decreases in renal tubular lesions and can help identify patients with AIN (Salvador López Giacoman et al.). This study aimed to confirm whether a low BCR is a good predictor of AIN in patients with a renal histology diagnosis of AIN. Materials and Methods: We conducted a retrospective study of hospitalized patients aged 18 years or older who were diagnosed with AIN based on renal histology. Results: 52 patients were included (60% male, mean age 42), and the optimal BUN/creatinine ratio (BCR) for classifying acute interstitial nephritis (AIN) was determined to be ≤14.5, with an area under the curve (AUC) of 0.92 (p=0.016). This cutoff showed a sensitivity of 91.3%, a specificity of 89.7%, a positive predictive value of 92.8%, and a negative predictive value of 89.7%, with an odds ratio (OR) of 21.8. Leukocyte casts in urine had an OR of 2.12 (p=0.05) for predicting AIN. Conclusion: A BUN/creatinine ratio (BCR) ≤14.5 was correlated with histological findings of acute interstitial nephritis.