Diagnostic accuracy of early urinary index changes in differentiating transient from persistent acute kidney injury in critically ill patients: multicenter cohort study

Abstract

Introduction: Urinary indices have limited effectiveness in separating transient acute kidney injury (AKI) from persistent AKI in ICU patients. Their time-course may vary with the mechanism of AKI. The primary objective of this study was to evaluate the diagnostic value of changes over time of the usual urinary indices in separating transient AKI from persistent AKI.

Methods: An observational prospective multicenter study was performed in six ICUs involving 244 consecutive patients, including 97 without AKI, 54 with transient AKI, and 93 with persistent AKI. Urinary sodium, urea and creatinine were measured at ICU admission (H0) and on 6-hour urine samples during the first 24 ICU hours (H6, H12, H18, and H24). Transient AKI was defined as AKI with a cause for renal hypoperfusion and reversal within 3 days.

Results: Significant increases from H0 to H24 were noted in fractional excretion of urea (median, 31% (22 to 41%) and 39% (29 to 48%) at H24, P<0.0001), urinary urea/plasma urea ratio (15 (7 to 28) and 20 (9 to 40), P<0.0001), and urinary creatinine/plasma creatinine ratio (50 (24 to 101) and 57 (29 to 104), P=0.01). Fractional excretion of sodium did not change significantly during the first 24 hours in the ICU (P=0.13). Neither urinary index values at ICU admission nor changes in urinary indices between H0 and H24 performed sufficiently well to recommend their use in clinical setting (area under the receiver-operating characteristic curve≤0.65).

Conclusion: Although urinary indices at H24 performed slightly better than those at H0 in differentiating transient AKI from persistent AKI, they remain insufficiently reliable to be clinically relevant.

Figure 1

Boxplot representation of urinary indices at baseline according to renal function. (a) Fractional excretion of urea (FeUrea) according to renal function (P = 0.03). (b) Fractional excretion of sodium (FeNa) according to renal function (P = 0.03). (c) The urine/plasma (U/P) urea ratio according to renal function (P < 0.0001). (d) The U/P creatinine ratio according to renal function (P < 0.0001). AKI, acute kidney injury. Whiskers represent 5th to 95th percentiles.

Figure 2

Changes in urinary indices during the first 24 hours after ICU admission according to renal function. (a) Fractional excretion of urea (FeUrea) according to renal function. (b) Fractional excretion of sodium (FeNa) according to renal function. (c) The urine/plasma (U/P) urea ratio according to renal function. (d) The U/P creatinine ratio according to renal function. AKI, acute kidney injury; H0, ICU admission; H6, H12, H18, and H24, 6-hour urine samples during the first 24 ICU hours. Data presented as mean ± 95% confidence interval.