Immediate Postoperative Serum Albumin as an Adjunctive Triage Aid for Early Acute Kidney Injury in Neonates After Non-Cardiac Surgery: A Retrospective Cohort Study

Technical Summary: Immediate Postoperative Serum Albumin as an Adjunctive Triage Aid for Early Acute Kidney Injury in Neonates

Problem Statement
Early detection of Acute Kidney Injury (AKI) in neonates following non-cardiac surgery is currently hindered by significant diagnostic delays. Standard AKI diagnosis relies on serum creatinine and urine output, both of which present temporal limitations: creatinine levels typically rise only 48–72 hours after renal injury, and timed urine collection is often impractical in neonates. Furthermore, a single creatinine value obtained at the first postoperative blood draw cannot confirm or exclude AKI without baseline comparison and serial trends. Consequently, the window for early preventive interventions often closes before AKI is confirmed by conventional criteria. While serum albumin is routinely measured in the first postoperative blood sample, its utility as an immediate risk stratification tool for early AKI in this specific population remains uninvestigated.

Methodology
This single-center, retrospective cohort study analyzed data from 843 neonates (postnatal age ≤28 days) who underwent non-cardiac surgery at Kunming Children's Hospital between November 2020 and December 2024.

• Inclusion/Exclusion: The study included neonates with surgical durations ≥30 minutes under general anesthesia. Exclusion criteria included pre-existing kidney dysfunction (preoperative AKI or congenital kidney disease), ASA status V, cardiac surgery with cardiopulmonary bypass, death within 24 hours, and missing key data.
• Exposure and Outcome: The primary exposure was immediate postoperative serum albumin (g/L), defined as the first value from the initial postoperative blood sample obtained upon transfer to the ICU or ward, prior to any postoperative fluid or albumin administration. The primary outcome was AKI occurring within 7 days post-surgery, defined by modified neonatal KDIGO criteria (urine output <1.0 mL/kg/h for ≥24 h or serum creatinine increase ≥0.3 mg/dL or ≥1.5-fold from baseline).
• Statistical Analysis: The study employed multivariable logistic regression with five sequential models adjusting for eight prespecified covariates: birth weight, preoperative creatinine, ASA status, surgery duration, intraoperative hypotension, intraoperative albumin administration, fluid balance, and red blood cell transfusion. Missing data (notably intraoperative urine output in 11.2% of cases) were handled via multiple imputation by chained equations. Discriminative performance was evaluated using Receiver Operating Characteristic (ROC) curves, comparing immediate postoperative albumin against preoperative albumin, absolute decrease, and percentage decrease.

Key Results

• Incidence: Among the 843 neonates, 77 (9.1%) developed AKI within 7 days postoperatively.
• Association: Lower immediate postoperative albumin was independently associated with increased odds of AKI. Each 1 g/L increase in postoperative albumin was associated with a 14% reduction in AKI odds (Odds Ratio [OR] 0.86, 95% CI 0.82–0.91; P < 0.001). This association remained robust across all adjusted models and sensitivity analyses.
• Discriminative Performance: Immediate postoperative albumin demonstrated superior discrimination compared to other metrics. It achieved an Area Under the Curve (AUC) of 0.713, significantly outperforming preoperative albumin (AUC 0.605), absolute decrease (AUC 0.606), and percentage decrease (AUC 0.626).
• Optimal Cutoff: The optimal cutoff for immediate postoperative albumin was determined to be 27 g/L. At this threshold, the test yielded:
  • Sensitivity: 67.5%
  • Specificity: 67.1%
  • Positive Predictive Value (PPV): 17.1%
  • Negative Predictive Value (NPV): 95.4% (at the observed 9.1% AKI prevalence).
• Subgroup Analysis: The inverse association between albumin and AKI was consistent across all predefined subgroups (surgery type, gestational age, ASA status, birth weight, hypotension, and albumin administration), with no significant interactions observed.

Significance and Claims
The paper posits that immediate postoperative serum albumin serves as a valuable adjunctive triage aid rather than a standalone diagnostic tool.

• Rule-Out Utility: The primary clinical value identified is the high Negative Predictive Value (95.4%) at the 27 g/L cutoff. This suggests that in neonates with a postoperative albumin level ≥27 g/L, the risk of developing AKI is very low, potentially allowing for the de-escalation of intensive monitoring in low-risk scenarios while awaiting serial creatinine trends.
• Complementary Role: The authors explicitly state that this metric does not replace creatinine-based monitoring. Instead, it complements it by providing an immediate risk signal at the time of the first postoperative blood draw, a time point where creatinine is often non-diagnostic due to the lack of baseline comparison or serial data.
• Pathophysiological Context: The association is interpreted as reflecting acute physiological responses to surgical stress, including systemic inflammation and capillary leakage, rather than pre-existing nutritional depletion.
• Modest Conclusions: The authors emphasize that the 27 g/L cutoff is derived from a single cohort with a specific AKI prevalence (9.1%) and requires prospective multicenter validation before general clinical implementation. They caution that a value <27 g/L should trigger enhanced surveillance rather than serve as a diagnosis of AKI, given the low PPV. The study concludes that while this simple, low-cost marker aids in early risk stratification, it must be used in conjunction with clinical judgment and standard creatinine-based assessment.