Diagnostic performance of fractional excretion of urea in the evaluation of critically ill patients with acute kidney injury: a multicenter cohort study

Abstract

IntroductionSeveral factors, including diuretic use and sepsis, interfere with the fractional excretion of sodium, which is used to distinguish transient from persistent acute kidney injury (AKI). These factors do not affect the fractional excretion of urea (FeUrea). However, there are conflicting data on the diagnostic accuracy of FeUrea.MethodsWe conducted an observational, prospective, multicenter study at three ICUs in university hospitals. Unselected patients, except those with obstructive AKI, were admitted to the participating ICUs during a six-month period. Transient AKI was defined as AKI caused by renal hypoperfusion and reversal within three days. The results are reported as medians (interquartile ranges).ResultsA total of 203 patients were included. According to our definitions, 67 had no AKI, 54 had transient AKI and 82 had persistent AKI. FeUrea was 39% (28 to 40) in the no-AKI group, 41% (29 to 54) in the transient AKI group and 32% (22 to 51) in the persistent AKI group (P = 0.12). FeUrea was of little help in distinguishing transient AKI from persistent AKI, with the area under the receiver operating characteristic curve being 0.59 (95% confidence interval, 0.49 to 0.70; P = 0.06). Sensitivity was 63% and specificity was 54% with a cutoff of 35%. In the subgroup of patients receiving diuretics, the results were similar.ConclusionsFeUrea may be of little help in distinguishing transient AKI from persistent AKI in critically ill patients, including those receiving diuretic therapy. Additional studies are needed to evaluate alternative markers or strategies to differentiate transient from persistent AKI.

Kinetic eGFR and Novel AKI Biomarkers to Predict Renal Recovery

“…However, only a few studies have tested the ability of biomarkers to predict AKI recovery. The limited interest in urinary biochemistry in critically ill patients was confirmed in our study (21)(22)(23)(24). Doppler ultrasonography may be a useful tool, and its ability to predict major adverse kidney events was interesting.…”

Transient versus Persistent Acute Kidney Injury and the Diagnostic Performance of Fractional Excretion of Urea in Critically Ill Patients

“…Our results are concordant to a recent multicenter study in a heterogeneous ICU population by Darmon et al [15], which concluded that FeU is not helpful in differentiating T-AKI from P-AKI. In contrast, Dewitte et al [11] in a single-center study concluded that an FeU of less than 40% was a sensitive and specific index for differentiating T-AKI from P-AKI.…”

“…Two our knowledge only two other studies have investigated the performance of FeU in distinguishing P-AKI from T-AKI in ICU patients [11,15]. Our results are concordant to a recent multicenter study in a heterogeneous ICU population by Darmon et al [15], which concluded that FeU is not helpful in differentiating T-AKI from P-AKI.…”

“…The different findings among the studies are probably caused by differences in study design, AKI definition and case mix. Darmon et al [15] included only the patients with AKI on the day of ICU admission, while Dewitte et al [11] and the present study also included patients developing AKI after ICU admission. In the present study the definition of recovery of oliguria (>0.5 ml/kg/h) was independent of the use of diuretics, while in the other two studies UO normalization had to be in the absence of diuretics.…”

“…The 2 days prior to this day were termed ‘day -2' and ‘day -1', respectively. Patients were classified as having P-AKI when AKI was sustained for more than 3 days according to RIFLE or when the patient died with AKI within 3 days [11,15]. The RIFLE class cannot be determined once continuous venovenous hemofiltration (CVVH) is started; therefore, we classified patients who received CVVH within 3 days after day 0 as P-AKI.…”