The association of albumin/creatinine ratio with postoperative AKI in children undergoing cardiac surgery

Abstract

Background and objectives: This study determined if preoperative and postoperative urine albumin/creatinine ratios (ACRs) predict postoperative AKI in children undergoing cardiac surgery (CS).

Design, setting, participants, & measurements: This was a three-center, prospective study (2007-2009) of 294 children undergoing CS (n=145 aged <2 years). Urine ACR was measured preoperatively and 0-6 hours after intensive care unit arrival. AKI outcomes were based on the Acute Kidney Injury Network serum creatinine (SCr) criteria (stage 1 AKI, ≥50% or 0.3 mg/dl SCr rise from baseline; and stage 2 or worse AKI, ≥SCr doubling or dialysis). AKI was predicted using preoperative and postoperative ACRs and postoperative ACR performance was compared with other AKI biomarkers.

Results: Preoperative ACR did not predict AKI in younger or older children. In children aged <2 years, first postoperative ACR ≥908 mg/g (103 mg/mmol) predicted stage 2 AKI development (adjusted relative risk, 3.4; 95% confidence interval, 1.2-9.4). In children aged ≥2 years, postoperative ACR ≥169 mg/g (19.1 mg/mmol) predicted stage 1 AKI (adjusted relative risk, 2.1; 95% confidence interval, 1.1-4.1). In children aged ≥2 years, first postoperative ACR improved AKI prediction from other biomarker and clinical prediction models, estimated by net reclassification improvement (P≤0.03), but only when serum cystatin C was also included in the model.

Conclusions: Postoperative ACR is a readily available early diagnostic test for AKI after pediatric CS that performs similarly to other AKI biomarkers; however, its use is enhanced in children aged ≥2 years and in combination with serum cystatin C.

Figure 1.

Study flow leading to the analysis population. The top of the figure displays the total study population. The diagram flows downward demonstrating the final patient numbers leading to the preoperative and postoperative analysis groups in the groups aged <2 years and ≥2 years, with respective ACR thresholds. To convert albumin to creatinine ratio to SI units, divide by 8.84. ACR, albumin/creatinine ratio.

Figure 2.

Preoperative and postoperative ACR in children aged <2 versus ≥2 years, by AKI status. Box plots of urine ACR from four time points (left to right: preoperative, first postoperative or day 1, the day after surgery or day 2, and 2 days after surgery or day 3) in patients with AKI (in blue) and patients who did not develop AKI (in green). The middle bar represents the median ACR value and the upper and lower box borders represent the 75th and 25th percentile values, respectively. The left panel includes children aged 1 month to <2 years; the right panel includes children aged ≥2 years. ACR, albumin/creatinine ratio; day 1, obtained the day of surgery, within 6 hours of arrival to intensive care unit; day 2, the day after surgery; day 3, 2 days after surgery.