Fractional Excretion of Urea and Acute Kidney Injury (AKI) in a Patient in the Intensive Care Unit (ICU)

 

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	Criteria
transient	recovery within 3 days with conventional therapy
recovery	(decrease in plasma creatinine by 50%) OR (urine output > 0.5 mL per kg per hour)
persistent	(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))

 

Interpretation:

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

 

Performance:

• 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%.