title: Urine biochemistry assessment in critically ill patients: controversies and future perspectives.
abstract: In the past, urine biochemistry was a major tool in acute kidney injury (AKI) management. Classic papers published some decades ago established the values of the urine indices which were thought to distinguish "pre-renal" (functional) AKI attributed to low renal perfusion and "renal" (structural) AKI attributed to acute tubular necrosis (ATN). However, there were a lot of drawbacks and limitations in these studies and some recent articles have questioned the utility of measuring urine electrolytes especially because they do not seem to adequately inform about renal perfusion nor AKI duration (transient vs. persistent). At the same time, the "pre-renal" paradigm has been consistently criticized because hypoperfusion followed by ischemia and ATN does not seem to explain most of the AKI developing in critically ill patients and distinct AKI durations do not seem to be clearly related to different pathophysiological mechanisms or histopathological findings. In this new context, other possible roles for urine biochemistry have emerged. Some studies have suggested standardized changes in the urine electrolyte composition preceding increases in serum creatinine independently of AKI subsequent duration, which might actually be due to intra-renal microcirculatory changes and activation of sodium-retaining mechanisms even in the absence of impaired global renal blood flow. In the present review, the points of controversy regarding urine biochemistry assessment were evaluated as well as future perspectives for its role in AKI monitoring. An alternative approach for the interpretation of measured urine electrolytes is proposed which needs further larger studies to be validated and incorporated in daily ICU practice.
authors.affiliation: Imed Research Group, Adult Intensive Care Unit, Hospital São Camilo, Av Pompéia 1178, São Paulo, SP, 05024-000, Brazil. alexandre.toledo@imedgroup.com.br.
authors.forename: Alexandre Toledo
authors.initials: AT
authors.lastname: Maciel
authors.affiliation: Imed Research Group, Adult Intensive Care Unit, Hospital São Camilo, Av Pompéia 1178, São Paulo, SP, 05024-000, Brazil.
authors.forename: Daniel
authors.initials: D
authors.lastname: Vitorio
mesh_terms: D058186:Acute Kidney Injury / Q000175:diagnosis* / Q000652:urine*; D015415:Biomarkers / Q000652:urine; D003422:Critical Care / Q000379:methods / Q000639:trends*; D016638:Critical Illness; D019317:Evidence-Based Medicine; D005544:Forecasting; D006801:Humans; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013673:Technology Assessment, Biomedical; D016482:Urinalysis / Q000379:methods* / Q000639:trends*
chemical_list: D015415:Biomarkers
keywords: Acute kidney injury; Critically ill patients; Fractional excretion; Monitoring; Review; Urine biochemistry; Urine electrolytes