Screening with blood urea nitrogen before intravenous contrast

In some settings, blood urea nitrogen (BUN) values are available well in advance of creatinine values. We wanted to determine whether BUN values can be used to screen for renal insufficiency for the purpose of intravenous contrast administration. From laboratory records, we derived and validated cutpoints for BUN values to detect creatinine values ≥2.0 mg/dL. “Sensitive” and “high-yield” cutpoints were derived using records from 5000 consecutive patients and validated using a random set of 2000 patients. BUN ≥15 mg/dL, the “sensitive” cutpoint, had sensitivity of 0.997 (95% confidence interval [CI], 0.987–1.0) and specificity of 0.56 (95% CI, 0.54–0.59). BUN ≥20 mg/dL, the “high-yield cutpoint,” had sensitivity of 0.98 (95% CI, 0.95–0.99) and specificity of 0.71 (95% CI, 0.69–0.73). Negative likelihood ratios for these cutpoints were 0.005 and 0.03, respectively. BUN values <15–20 mg/dL provide strong evidence against renal insufficiency.