Hemolysis Index, Carboxyhemoglobin, and Methemoglobin for the Early Identification of Patients at Risk for Cardiac Surgery–Associated Acute Kidney Injury

Abstract

Hemolysis is a contributor to CS-AKI. Biochemistry analyzers provide a hemolysis index to quantify in vitro hemolysis, a condition that can, for example, affect the accuracy of potassium concentration measurements. We aimed to assess whether the postoperative plasma level of the hemolysis index (HIpostoperative) could aid the early recognition of patients at risk for cardiac surgery-associated acute kidney injury (CS-AKI) and also to evaluate other hemolysis indicators: plasma carboxyhemoglobin (COHbpostoperative) and methemoglobin (MetHbpostoperative). One-year retrospective study. University hospital. Patients undergoing elective cardiac surgery. None. In 1090 patients, the median HIpostoperative was higher in patients who developed CS-AKI compared to patients who did not (11 mg/dL [interquartile range (IQR), 5-38 mg/dL] v 7 mg/dL [IQR, 3-16 mg/dL]; p < 0.001). HIpostoperative refined the early recognition of CS-AKI: the area under the precision-recall curve (AUPRC) for HIpostoperative was 37% (95% confidence interval [CI], 31%-42%), whereas the AUPRC associated with no discriminative power, equal to the prevalence of CS-AKI in the whole population, was 21%. Among the 611 patients with measurements for all 3 biomarkers, the AUPRC of HIpostoperative was higher than that of COHbpostoperative or MetHbpostoperative (+6.6% and +7.4% respectively; p < 0.0001 for both). Unlike COHbpostoperative or MetHbpostoperative, the incorporation of HIpostoperative into a model (trained on a sample then validated in another sample) of CS-AKI early recognition significantly enhanced its performance, with a +1.9% (95% CI, 1.6%-2.1%) increase in AUPRC (p < 0.0001). Elevated HIpostoperative represents an early alert signal for the development of CS-AKI. Our findings support the incorporation of HIpostoperative, a readily available biomarker, into predictive scores of CS-AKI.