Traditional biomarkers, such as urine chemistries and urine microscopic elements, are used in the diagnosis and care of patients with AKI. Urine chemistries, such as fractional excretion of sodium and fractional excretion of urea, are useful for differentiating prerenal AKI from acute tubular necrosis only in select patients. Urine microscopy using a quantitative evaluation of the urine sediment for renal tubular epithelial cells, renal tubular epithelial cell casts, and granular casts has recently been shown to differentiate prerenal AKI from acute tubular necrosis and also provide prognostic information. Urine microscopy has also been noted to compare favorably with new urine biomarkers for diagnosis and prognosis of AKI. Thus, current information on urine diagnostics suggests that urine chemistries have a limited role in differential diagnosis of AKI, whereas urine microscopy and new urine biomarkers may be used together to differentiate prerenal AKI from acute tubular necrosis and predict such outcomes as worsened AKI, acute dialysis, and death.