Supplementary Material for: Saliva Urea Nitrogen Continuously Reflects Blood Urea Nitrogen after Acute Kidney Injury Diagnosis and Management: Longitudinal Observational Data from a Collaborative, International, Prospective, Multicenter Study

Background: Acute kidney injury (AKI) is a growing global concern and often reversible. Saliva urea nitrogen (SUN) measured by a dipstick may allow rapid diagnosis. We studied longitudinal agreement between SUN and blood urea nitrogen (BUN) and the diagnostic performance of both. Methods: Agreement between SUN and BUN and diagnostic performance to diagnose AKI severity in AKI patients in the United States and Brazil were studied. Bland-Altman analysis and linear mixed effects models were employed to test the agreement between SUN and BUN. Receiver operating characteristics statistics were used to test the diagnostic performance to diagnose AKI severity. Results: We found an underestimation of BUN by SUN, decreasing with increasing BUN levels in 37 studied patients, consistent on all observation days. The diagnostic performance of SUN (AUC 0.81, 95% CI 0.63-0.98) was comparable to BUN (AUC 0.85, 95% CI 0.71-0.98). Conclusion: SUN reflects BUN especially in severe AKI. It also allows monitoring treatment responses. Video Journal Club ‘Cappuccino with Claudio Ronco' at http://www.karger.com/?doi=445041.