Dewitte et al used the fractional excretion of urea to separate transient from persistent acute kidney injury (AKI) for patients in the intensive care unit (ICU). This can help to identify a patient who may benefit from more aggressive management. The authors are from Place Amelie Raba-Leon and Universitaire de Bordeaux in Bordeaux, France.


Patient selection: acute kidney injury (AKI) in the ICU in a patient without end-stage renal disease, chronic kidney disease or a urinary tract malignancy


Type of AKI



recovery within 3 days with conventional therapy


(decrease in plasma creatinine by 50%) OR (urine output > 0.5 mL per kg per hour)


(persistent elevation of plasma creatinine) OR (oliguria)


fractional excretion of urea (FE-urea) =

= (100% * (((urine urea in mmol/L) / (plasma urea in mmol/L)) / ((urine creatinine in µmol/L) / (plasma creatinine in µmol/L)))) =

= 100% * (urine urea in mmol/L) * (plasma creatinine in µmol/L) / ((plasma urea in mmol/L) * (urine creatinine in µmol/L))



• A fractional excretion of urea < 40% identified a patient with transient AKI, especially if patients treated with diuretics.



• The area under the ROC curve (outcome transient AKI) was 0.78 for fractional excretion of urea.

• For patients not treated with diuretics the sensitivity was 83% and specificity 75%.

• For patients treated with diuretics the sensitivity was 80% and specificity 85%.


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