Iron metabolism-related indicators as predictors of the incidence of acute kidney injury after cardiac surgery: a meta-analysis

Background: Some studies have found that ferroptosis plays an important role in the incidence of acute kidney injury (AKI) after cardiac surgery. However, whether iron metabolism-related indicators can be used as predictors of the incidence of AKI after cardiac surgery remains unclear. Objectives: We aimed to systematically evaluate whether iron metabolism-related indicators can be used as predictors of the incidence of AKI after cardiac surgery via meta-analysis. Search methods: The PubMed, Embase, Web of Science, and Cochrane Library databases were searched from January 1971 to February 2023 to identify prospective observational and retrospective observational studies examining iron metabolism-related indicators and the incidence of AKI after cardiac surgery among adults. Data Extraction and Synthesis: The following data were extracted by two independent authors (ZLM and YXY): date of publication, first author, country, age, sex, number of included patients, iron metabolism-related indicators, outcomes of patients, patient types, study types, sample, and specimen sampling time. The level of agreement between authors was determined using Cohen's. value. The Newcastle-Ottawa Scale (NOS) was used to evaluate the quality of studies. Statistical heterogeneity across the studies was measured by the I2 statistic. The standardized mean difference (SMD) and 95% confidence interval (CI) were used as effect size measures. Meta-analysis was performed using Stata 15. Results: After applying the inclusion and exclusion criteria, 9 articles on iron metabolism-related indicators and the incidence of AKI after cardiac surgery were included in this study. Meta-analysis revealed that after cardiac surgery, baseline serum ferritin (mu g/L) (I-2 = 43%, fixed effects model, SMD = -0.3, 95% CI:-0.54 to -0.07, p = 0.010), preoperative and 6-hour postoperative fractional excretion (FE) of hepcidin (%) (I-2 = 0.0%, fixed effects model, SMD = -0.41, 95% CI: -0.79 to -0.02, p = 0.038; I-2 = 27.0%, fixed effects model, SMD = -0.49, 95% CI: -0.88 to -0.11, p = 0.012), 24-hour postoperative urinary hepcidin (mu g/L) (I-2 = 0.0%, fixed effects model, SMD = -0.60, 95% CI: -0.82 to -0.37, p < 0.001) and urine hepcidin/urine creatinine ratio (mu g/mmoL) (I-2 = 0.0%, fixed effects model, SMD = -0.65, 95% CI: -0.86 to - 0.43, p < 0.001) were significantly lower in patients who developed to AKI than in those who did not. Conclusion: After cardiac surgery, patients with lower baseline serum ferritin levels (mu g/L), lower preoperative and 6-hour postoperative FE of hepcidin (%), lower 24-hour postoperative hepcidin/ urine creatinine ratios (mu g/mmol) and lower 24-hour postoperative urinary hepcidin levels (mu g/L) are more likely to develop AKI. Therefore, these parameters have the potential to be predictors for AKI after cardiac surgery in the future. In addition, there is a need for relevant clinical research of larger scale and with multiple centers to further test these parameters and prove our conclusion.