Lactate-to-albumin ratio index correlates with the occurrence and prognosis of acute kidney injury complicated by cardiac surgery

doi:10.21203/rs.3.rs-5304928/v1

Background

The lactate-to-albumin ratio (LAR), an emerging biomarker, has been recognized as an indicator of poor prognosis in various critical illnesses. However, the relationship between LAR and the incidence and prognosis of cardiac surgery-associated acute kidney injury (AKI) remains uncertain. This study aims to elucidate this relationship through a comprehensive analysis of a large cohort from the MIMIC database.

Methods

This study utilized a retrospective cohort design to analyze adult patients admitted to the intensive care unit (ICU) following cardiac surgery. Statistical methods such as logistic regression, restricted cubic spline (RCS) analysis, and subgroup analysis were employed to assess the predictive value of LAR for the occurrence of AKI and adverse outcomes after cardiac surgery.

Results

A total of 11,624 cardiac surgery patients were included, among which 5,965 developed acute kidney injury. The LAR index was significantly higher in the cardiac surgery population that developed AKI compared to those who did not. Logistic regression analysis indicated that LAR was significantly associated with in-hospital and ICU mortality, even after adjusting for potential confounders across multiple models. RCS analysis revealed a non-linear relationship between elevated LAR and increased risks of in-hospital and ICU mortality in patients with AKI following cardiac surgery. Correlation analyses demonstrated a significant association between LAR and length of stay in the hospital (LOS-H), length of stay in the ICU (LOS-ICU), and SOFA scores. ROC curve analysis indicated that the LAR index had good predictive value for mortality in the AKI population following cardiac surgery. Subgroup analyses consistently showed that elevated LAR was associated with increased risks of in-hospital and ICU mortality in older adults, females, and populations regardless of hypertension, chronic kidney disease, diabetes, or chronic heart failure.

Conclusions

Elevated LAR is associated with the incidence of cardiac surgery-associated acute kidney injury and the higher mortality risk in this population. Our findings highlight the previously unrecognized role of LAR in predicting mortality in patients with AKI following cardiac surgery, warranting further validation.

Health sciences/Biomarkers/Prognostic markers

Health sciences/Nephrology/Kidney diseases/Acute kidney injury

Health sciences/Cardiology/Cardiovascular biology/Cardiovascular diseases

Lactate-to-albumin ratio

Acute kidney injury

Cardiac surgery

Mortality

Acute kidney injury (AKI) is a common complication following cardiac surgery and significantly impacts patient outcomes. It is reported that the incidence of AKI can reach as high as 40%, exacerbating the risk of hospital-acquired infections, prolonged hospital stays, and in-hospital mortality(1).The primary cause is acute kidney failure resulting from inadequate renal perfusion, which can lead to multi-organ failure and increased mortality(2). Since significant clinical manifestations often appear several days after kidney injury, and there is a lack of specific treatment options, early therapeutic interventions and renal protective measures are limited. Therefore, accurate and early identification of risk factors for AKI is crucial. The lactate/albumin ratio (LAR), an emerging biomarker for predicting adverse outcomes, has been shown to have significant prognostic value in diseases such as acute myocardial infarction(3), cardiac arrest(4), sepsis(5), and septic shock(6). Elevated LAR is associated with increased lactate levels and decreased serum albumin levels. In patients with AKI, elevated lactate levels often indicate tissue hypoperfusion and inadequate oxygenation, while hypoalbuminemia may suggest malnutrition or chronic inflammation—both of which are linked to poor outcomes in AKI patients(7, 8). Therefore, the lactate/albumin ratio holds potential as a key biomarker for assessing the occurrence of AKI and predicting adverse outcomes following cardiac surgery. We conducted a retrospective study to explore the association between LAR and the risk of AKI and its adverse outcomes in patients undergoing cardiac surgery.

Data source

This study utilized data from MIMIC-IV version 2.2, an electronic health record dataset of over 50,000 ICU patients admitted to Beth Israel Deaconess Medical Center (BIDMC) in Boston from 2008 to 2019. The BIDMC Institutional Review Board approved the sharing of research data and waived informed consent. Author DHL accessed the database under certificate number 63768415. Following STROBE guidelines(9).

Inclusion Criteria:

1. Age > 18 years and first ICU admission.

2. Undergoing cardiac surgery, including coronary artery bypass grafting (CABG), aortic surgery, valve repair or replacement (single or multiple), or combined procedures.

Exclusion Criteria:

1. ICU stay of less than 24 hours.

2. Missing lactate or albumin data upon admission.

3. Missing data > 20%.

4. Patients diagnosed with end-stage renal disease (ESRD).

For the diagnosis of AKI, we followed the criteria set by the 2012 Kidney Disease: Improving Global Outcomes (KDIGO) guidelines(10). The criteria include: (1) an increase in serum creatinine (SCr) of ≥ 0.3 mg/dl within 48 hours; (2) an increase in SCr to ≥ 1.5 times the baseline level within 7 days of ICU admission; and (3) urine output less than 0.5 mL/kg/h for 6 consecutive hours. AKI and cardiac surgery data were extracted from the MIMIC-IV database using International Classification of Diseases (ICD) codes (ICD-9 or ICD-10).

Outcomes

The primary outcomes assessed were in-hospital and ICU mortality rates. Secondary outcomes included the length of hospital stay (LOS-H) and the length of ICU stay (LOS-ICU).

Data extraction

Data extraction was conducted using DecisionLinnc1.0 software, which is an integrated platform that combines various programming language environments, allowing for data processing, analysis, and machine learning through a user-friendly visual interface. The extracted data are detailed below: (a) Demographic Data: Includes age, gender, heart rate (HR), respiratory rate (RR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), and peripheral oxygen saturation (SpO2).(b)Comorbidities: Comprises conditions such as hypertension, type 2 diabetes mellitus (T2DM), chronic heart failure (CHF), chronic obstructive pulmonary disease (COPD), ischemic heart disease (IHD), chronic kidney disease (CKD), and stroke.(c)Laboratory Data: Encompasses white blood cell count (WBC), platelet count (PLT), hemoglobin (Hb), aspartate aminotransferase (AST), alanine aminotransferase (ALT), blood urea nitrogen (BUN), creatinine, lactate (LAC), fasting blood glucose (FBG), glycosylated hemoglobin (HbA1C), sodium, potassium, and anion gap (AG).(d)Severity of Illness: Measured using the Sequential Organ Failure Assessment (SOFA) score. The lactate-to-albumin ratio (LAR) is defined as follows: LAR = (admission lactate (mmol/L) / albumin (g/dl)).

Statistical Analysis

Continuous variables are presented as medians with interquartile ranges, and the Mann-Whitney U test was used to compare differences between groups. Categorical variables are expressed as counts and percentages, with chi-square and Fisher’s exact tests employed for intergroup comparisons. Missing values were addressed using multiple imputation methods, while data with missing values exceeding 20% were excluded. Statistical significance was defined as a two-tailed P-value < 0.05. For logistic analysis, both univariate and multivariate models were established to assess the predictive role of the lactate-to-albumin ratio (LAR) on the occurrence of AKI and adverse outcomes following cardiac surgery. Restricted cubic spline (RCS) analysis was utilized to identify potential linear associations between LAR levels and mortality in patients with AKI post-surgery, stratifying the sample based on the optimal threshold. Receiver operating characteristic (ROC) analysis evaluated the predictive capability of LAR for AKI occurrence and adverse outcomes during hospitalization. Correlation analysis assessed the relationship between LAR and continuous indicators, including length of stay in hospital (LOS-H), length of stay in ICU (LOS-ICU), and SOFA scores. Additionally, subgroup analyses were conducted based on sex, age, and comorbidities to evaluate potential differences in the incidence of adverse outcomes among AKI patients during ICU and hospital stays.

Elevated LAR Levels Linked to Higher Risk of AKI After Cardiac Surgery.

We extracted data on 11,624 patients who underwent cardiac surgery from the MIMIC-IV database (Fig. 1). Variance inflation factor (VIF) values are displayed in Table S1, confirming the absence of multicollinearity between variables. Among these patients, 5,965 developed AKI. As shown in Table 1, there were some differences in baseline characteristics between those with and without AKI post-surgery.

Individuals who developed AKI had significantly higher LAR levels compared to those who did not (P < 0.001), indicating a statistically significant difference. Based on this observation, we further assessed the association between LAR levels and the risk of AKI in post-cardiac surgery patients through logistic regression analysis. Univariate logistic analysis revealed that the LAR index was a significant predictor of AKI in post-surgery patients (Model 1: OR 2.150, P < 0.001). However, after adjusting for confounding factors, multivariate logistic analysis showed that the LAR index was not an independent predictor of AKI (Model 3: OR 1.405, P = 0.064, Table 2). The ROC curve indicated that the LAR index had a low predictive value for identifying AKI occurrence in this population, with an AUC of 0.532 (95% CI: 0.517–0.546, Figure S1, Table S5).

Overall, although elevated LAR levels are associated with an increased risk of AKI in cardiac surgery patients, LAR cannot be considered an independent risk factor for predicting AKI occurrence.

Table 1 Baseline characteristics between patients after cardiac surgery with and without AKI

Characteristics	All surgical patients (n=7953)	surgical patients without AKI(n=1988)	surgical patients with AKI(n=5965)	P valve
Demographic data
Age, y	68.0(61.0-76.0)	66.0(58.0-73.0)	69.0(61.0-77.0)	＜0.001
Gender, n(%)				0.024
Female	2298（28.9）	535(26.9)	1763(29.6)
Male	5655（71.1）	1453(73.1)	4202(70.4)
SBP, mmHg	112.0(102.0-123.0)	112.0(103.0-123.0)	112.0(102.0-124.0)	0.874
DBP, mmHg	59.0(52.0-66.0)	59.0(53.0-66.0)	58.0(52.0-65.0)	＜0.001
MAP, mmHg	77.0(70.0-85.0)	78.0(71.0-85.0)	77.0(69.0-85.0)	0.002
HR, bpm	80.0(74.0-86.0)	80.0(73.0-86.0)	80.0(74.0-86.0)	0.338
RR, bpm	15.0(12.0-17.0)	14.0(12.0-17.0)	15.0(12.0-17.0)	0.136
SpO2, %	100.0(99.0-100.0)	100.0(100.0-100.0)	100.0(99.0-100.0)	＜0.001
SOFA	5.0(3.0-7.0)	4.0(3.0-6.0)	5.0(3.0-7.0)	＜0.001
Comorbidities, n(%)
Hypertension	4822(60.6)	1199(60.3)	3623(60.7)	0.736
T2DM	2506(31.5)	536(26.9)	1970(33.0)	＜0.001
CHF	1831(23.0)	362(18.2)	1469(24.6)	＜0.001
Stroke	595(7.5)	132(6.6)	463(7.8)	0.100
COPD	781(9.8)	168(8.5)	613(10.3)	0.018
CKD	894(11.2)	166(8.4)	728(12.2)	＜0.001
IHD	5955(74.9)	1469(73.9)	4486(75.2)	0.243
Laboratory data
WBC, M/mcl	7.1(5.8-8.7)	7.0(5.8-8.6)	7.1(5.8-8.7)	0.148
PLT, K/mcl	142.0(114.0-177.0)	141.0(115.0-176.0)	142.0(113.0-177.0)	0.928
Hb, g/dL	9.5(8.4-10.8)	9.7(8.6-10.8)	9.5(8.3-10.7)	＜0.001
AST	22.0(18.0-29.0)	22.0(18.0-28.0)	22.0(18.0-29.0)	0.687
ALT	20.0(15.0-28.0)	21.0(15.0-28.0)	20.0(14.0-28.0)	0.002
TBIL	0.5(0.4-0.7)	0.5(0.3-0.7)	0.5(0.4-0.7)	0.363
LAC	1.3(1.0-1.7)	1.3(1.0-1.7)	1.3(1.0-1.7)	0.543
ALB	4.0(3.6-4.3)	4.1(3.7-4.4)	3.9(3.5-4.3)	＜0.001
LAR	0.3(0.2-0.4)	0.3(0.2-0.4)	0.3(0.3-0.4)	＜0.001
FBG	100.0(90.0-115.0)	98.0(89.0-112.0)	101.0(90.0-115.0)	＜0.001
HbA1c	5.8(5.5-6.5)	5.7(5.4-6.3)	5.8(5.5-6.5)	＜0.001
BUN	14.0(12.0-18.0)	14.0(11.0-17.0)	15.0(12.0-18.0)	＜0.001
Creatinine	0.8(0.7-1.0)	0.8(0.7-0.9)	0.8(0.7-1.0)	＜0.001
Sodium	138.0(136.0-139.0)	137.0(136.0-139.0)	138.0(136.0-139.0)	0.043
Potassium	4.0(3.7-4.2)	4.0(3.7-4.2)	4.0(3.7-4.2)	＜0.001
Calcium	8.3(8.0-8.6)	8.3(8.0-8.7)	8.3(8.0-8.6)	0.277
AG	11.0(9.0-12.0)	10.0(9.0-12.0)	11.0(9.0-12.0)	＜0.001

Table 2

Logistic regression analyses regarding the association between the LAR index and the occurrence of AKI in surgical populations
LAR index	OR	95%CI	P valve
Model 1	2.150	1.540–3.040	<0.001
Model 2	1.916	1.362–2.722	0.002
Model 3	1.405	0.985–2.024	0.064

LAR index, lactate to albumin ratio index ;OR, odds ratio; CI, confidence interval

Model 1: unadjusted

Model 2: Adjusted for age, gender, DBP,MAP and SpO2

Model 3: Adjusted for age, gender, DBP, MAP, creatine, sodium, potassium, calcium, Hb, SpO2, SOFA, BUN, FBG, ALT,AG, CHF, CKD, T2DM, COPD

Baseline Characteristics and Clinical Outcomes of Patients with AKI after Cardiac Surgery

Among the 5,965 patients who developed AKI, 30 died during hospitalization, and 29 died during their ICU stay. As shown in Tables S2 and S3, LAR levels were significantly higher in non-survivors compared to survivors, both during hospitalization and ICU stays (P < 0.001).

We divided patients into three groups based on LAR tertiles, revealing baseline characteristic differences between the groups (Table 3). As shown in Table 4, patients with higher LAR levels had significantly higher in-hospital and ICU mortality rates, as well as longer LOS-H and LOS-ICU, compared to those with lower LAR levels (P < 0.001). Figure 2 further illustrates a rising trend in LOS-H and LOS-ICU with increasing LAR tertiles. Although this trend was not observed for in-hospital and ICU mortality rates, we did find that mortality rates in Tertile 3 were substantially higher than those in Tertiles 1 and 2, with in-hospital mortality notably exceeding ICU mortality.

Overall, these findings suggest that elevated LAR may be associated with worse outcomes in patients who develop AKI following cardiac surgery.

Table 3

Baseline characteristics of patients with AKI after cardiac surgery stratified based on the tertiles of the LAR index
Characteristics	Tertile 1 (n = 1980)	Tertile 2 (n = 2027)	Tertile 3 (n = 1958)	P valve
Demographic data
Age, y	69.0(61.0–77.0)	69.0(62.0–77.0)	70.0(62.0–77.0)	0.546
Gender, n(%)				0.068
Female	619(31.3)	566(27.9)	578(29.5)
Male	1361(68.7)	1461(72.1)	1380(70.5)
SBP, mmHg	113.0(102.7–125.0)	112.0(103.0-124.0)	112.0(101.0-123.0)	0.051
DBP, mmHg	58.0(52.0–65.0)	58.0(52.0–66.0)	58.0(52.0–65.0)	0.588
MAP, mmHg	77.0(769.0–85.0)	77.0(69.0–85.0)	77.0(69.0–85.0)	0.206
HR, bpm	80.0(74.0–86.0)	80.0(73.0–86.0)	80.0(74.0–86.0)	0.338
RR, bpm	14.0(12.0–16.0)	15.0(12.0–17.0)	15.0(12.0–17.0)	0.003
SpO2, %	100.0(100.0-100.0)	100.0(99.0-100.0)	100.0(99.0-100.0)	<0.001
SOFA	5.0(3.0–7.0)	5.0(3.0–7.0)	5.0(4.0–7.0)	<0.001
Comorbidities, n(%)
Hypertension	1187(59.9)	1240(61.174)	1196(61.083)	0.679
T2DM	552(27.9)	668(33.0)	750(38.3)	<0.001
CHF	439(22.2)	512(25.3)	518(26.5)	0.006
Stroke	151(7.7)	162(8.0)	150(7.7)	0.892
COPD	198(10.0)	203(10.0)	212(10.8)	0.619
CKD	237(12.0)	254(12.5)	237(12.1)	0.851
IHD	1428(72.1)	1546(76.3)	1512(77.2)	<0.001
Laboratory data
WBC, M/mcl	6.8(5.5–8.2)	7.1(5.9–8.7)	7.4(6.2–9.1)	<0.001
PLT, K/mcl	140.0(112.0-177.0)	140.0(113.0-174.0)	145.0(115.0-180.0)	0.059
Hb, g/dL	9.4(8.2–10.7)	9.5(8.4–10.7)	9.6(8.3–10.8)	0.037
AST	22.0(18.0–28.0)	22.0(18.0–29.0)	23.0(18.0–30.0)	0.003
ALT	19.0(14.0–26.0)	19.0(14.0–28.0)	21.0(15.0–30.0)	<0.001
TBIL	0.5(0.4–0.7)	0.5(0.4–0.7)	0.5(0.4–0.7)	0.558
LAC	0.9(0.8-1.0)	1.3(1.2–1.5)	1.8(1.6–2.1)	<0.001
ALB	4.1(3.8–4.4)	3.9(3.6,4.3)	3.8(3.2–4.1)	<0.001
FBG	98.0(88.0-111.0)	101.0(90.0-115.0)	104.0(93.0-120.0)	<0.001
HbA1c	5.7(5.4–6.2)	5.9(5.5–6.5)	6.0(5.6–6.8)	<0.001
BUN	15.0(12.0–19.0)	15.0(12.0–18.0)	15.0(12.0–18.0)	0.827
Creatinine	0.8(0.7-1.0)	0.8(0.7-1.0)	0.8(0.7-1.0)	0.473
Sodium	138.0(136.0-139.0)	137.0(136.0-139.0)	138.0(136.0-139.0)	0.097
Potassium	4.0(3.7–4.2)	4.0(3.8–4.2)	4.0(3.7–4.3)	0.580
Calcium	8.3(8.0-8.6)	8.3(8.0-8.7)	8.3(8.0-8.6)	0.573
AG	10.0(9.0–12.0)	11.0(9.0–13.0)	11.0(10.0–13.0)	<0.001

Table 4

Clinical outcomes of patients with AKI after cardiac surgery stratified based on the tertiles of the LAR index
Outcomes	Tertile 1	Tertile 2	Tertile 3	P value
Primary outcomes, n(%)
In-hospital mortality	5(0.3)	1(0.1)	24(1.2)	< 0.001
ICU mortality	6(0.3)	2(0.1)	21(1.1)	< 0.001
Secondary outcomes, days
LOS-H	6.7(5.2–8.9)	7.0(5.3–9.9)	7.6(5.6–10.9)	< 0.001
LOS-ICU	2.1(1.3–3.1)	2.1(1.3–3.3)	2.2(1.3–3.5)	< 0.001

Elevated LAR Associated with Increased Mortality in Post-Cardiac Surgery AKI Patients

To further evaluate the association between LAR levels and survival outcomes, we performed logistic regression analysis (Table 5). Univariate logistic regression showed a significant correlation between mortality and the LAR index. For each unit increase in LAR, the odds ratio (OR) for in-hospital mortality was 5.76, and the OR for ICU mortality was 5.38. Compared to those in the lowest tertile, individuals in the highest tertile had a 4.90-fold higher risk of in-hospital mortality and a 3.57-fold higher risk of ICU mortality. After adjusting for confounding factors, this association remained robust. In the fully adjusted Model 3, each unit increase in LAR was associated with an OR of 3.64 for in-hospital mortality and 3.17 for ICU mortality. Additionally, those in the highest tertile had a 4.53-fold higher risk of in-hospital mortality and a 3.34-fold higher risk of ICU mortality compared to the lowest tertile. There was a clear trend of increasing mortality risk with rising LAR tertiles (P for trend < 0.05).

Furthermore, pearson correlation analysis demonstrated a significant relationship between LAR and factors such as LOS-H, LOS-ICU, and SOFA scores (Table S4). The ROC curve indicated that the LAR index had good predictive value for mortality in AKI patients following cardiac surgery (in-hospital mortality AUC: 0.742, 95% CI: 0.641–0.842; ICU mortality AUC: 0.712, 95% CI: 0.603–0.820, Fig. 3, Table S5).

Overall, these findings suggest that elevated LAR is strongly associated with poor prognosis in post-surgery AKI patients, particularly in terms of in-hospital and ICU mortality.

Table 5

Logistic regression analyses for the association between the LAR index and mortality in patients with AKI after cardiac surgery
Variables	Model 1		Model 2		Model 3
Variables	OR(95%CI)	P value	OR(95%CI)	P value	OR(95%CI)	P value
In-hospital mortality
Per 1 Unit increase	5.76(2.68–11.40)	<0.001	3.66(1.33–8.89)	0.008	3.64(1.24–9.68)	0.013
Tertile 1	1 reference		1 reference		1 reference
Tertile 2	0.20(0.01–1.20)	0.140	0.19(0.01–1.21)	0.135	0.19(0.01–6.23)	0.136
Tertile 3	4.90(2.03–14.58)	0.001	4.23(1.73–12.67)	0.004	4.53(1.74–14.31)	0.004
P for trend	<0.001		<0.001		<0.001
ICU mortality
Per 1 Unit increase	5.38(2.41–10.70)	<0.001	3.46(1.22–8.61)	0.013	3.17(1.01–8.78)	0.013
Tertile 1	1 reference		1 reference		1 reference
Tertile 2	0.32(0.05–1.41)	0.170	0.32(0.05–1.40)	0.170	0.19(0.01–1.23)	0.181
Tertile 3	3.57(1.52–9.74)	0.006	3.10(1.31–8.52)	0.016	3.34(1.32–9.76)	0.016
P for trend	0.001		0.004		0.004

Model 1: unadjusted

Model 2: Adjusted for age, gender, HR and SpO2

Model 3: Adjusted for age, gender, HR, SpO2, SOFA, FBP, HbA1C, creatine, sodium, potassium, AG, Hb, PLT, BUN, CHF, CKD, T2DM, COPD, Hypertension, Stroke

Restricted Cubic Spline Analysis

To further illustrate the relationship between LAR and adverse outcomes, we employed restricted cubic spline (RCS) analysis (Fig. 4). After adjusting for covariates in Model 3, we identified a nonlinear correlation between LAR and both in-hospital and ICU mortality. Threshold effect analysis revealed a turning point for ICU mortality at an LAR value of 0.6 and for in-hospital mortality at 0.46. The findings indicate that when LAR is below these thresholds, mortality risk remains relatively low, but once LAR exceeds these points, the risk increases sharply.

Subgroup Analysis

To assess the robustness of the association between LAR and in-hospital and ICU mortality across different subgroups, we further estimated the predictive role of LAR on mortality outcomes (Figs. 5 and 6). The results consistently showed that elevated LAR was associated with increased in-hospital and ICU mortality in elderly patients, females, and individuals without chronic kidney disease, diabetes, or chronic heart failure. Notably, a strong correlation between LAR and in-hospital mortality was observed in patients with chronic heart failure. However, no significant interactions were found across subgroups defined by age, gender, hypertension, diabetes, chronic kidney disease, or chronic heart failure (P > 0.05).

We conducted a large retrospective cohort study using data from 11,624 post-cardiac surgery patients in the MIMIC-IV database and found that LAR levels were significantly higher in patients who developed AKI compared to those who did not. The LAR index demonstrated a moderate ability to distinguish mortality among AKI patients. Even after adjusting for potential confounders, elevated LAR levels were closely associated with increased risks of in-hospital and ICU mortality in post-cardiac surgery AKI patients. This is the first study to explore the relationship between LAR and adverse outcomes in this population, highlighting its previously unrecognized importance.

Each year, over 2 million cardiac surgeries are performed globally(11), with cardiac surgery-associated acute kidney injury (CSA-AKI) occurring in up to 40% of cases, making it the second leading cause of AKI in the ICU. Perioperative mortality for severe cardiac surgery-associated acute kidney injury is 3 to 8 times higher(12), and around 3% of patients require temporary renal replacement therapy (RRT)(13). Even patients who fully recover kidney function remain at elevated risk for chronic kidney disease (CKD) and mortality(14, 15).The mechanisms behind CSA-AKI are not fully understood but are believed to involve nephrotoxic medications(16–19), excessive preoperative diuresis, intraoperative hemofiltration(11), inflammatory responses due to blood component interactions(20), and ischemia-reperfusion injury. These factors collectively exacerbate renal dysfunction throughout the perioperative period. With no specific pharmacological interventions to prevent CSA-AKI, early detection of subtle renal changes (subclinical AKI) is crucial. Biomarkers such as cystatin C (CysC), neutrophil gelatinase-associated lipocalin (NGAL), and kidney injury molecule-1 (KIM-1) can detect renal impairment before increases in serum creatinine.

The lactate-to-albumin ratio (LAR) has emerged as a significant indicator for predicting poor outcomes across various critical illnesses. Elevated lactate levels reflect tissue hypoperfusion(21), while albumin is essential for maintaining plasma osmotic pressure (22) and correlates with disease prognosis(23). However, both biomarkers are influenced by multiple factors(24), limiting their predictive accuracy when used in isolation. Integrating these indicators, studies have found that LAR serves as an independent predictor of all-cause mortality within 28 days for acute pancreatitis patients, outperforming the SOFA score(25). In acute respiratory distress syndrome (ARDS), LAR correlates positively with 28-day mortality, exceeding predictions based on lactate or albumin alone and comparable to the SPASII score (26). LAR has also been shown to be a poor prognostic indicator of all-cause mortality in patients with sepsis, whether admitted in the emergency department or on the ward, and correlates with the severity of sepsis(5, 27).LAR is also linked to other conditions, including burns and traumatic brain injury(28, 29). A recent study found that LAR correlates with both short-term and long-term mortality in critically ill patients with cardiac surgery-associated acute kidney injury(30), aligning with our results.

However, no studies have yet investigated the relationship between LAR and adverse outcomes in patients with CSA-AKI. Our subgroup analysis revealed that, in addition to older adults and females, elevated LAR was associated with increased in-hospital and ICU mortality in patients without comorbidities. This association may stem from patients' nutritional status, chronic inflammation, or interactions with perioperative factors. A meta-analysis indicated that cardiac surgery-associated acute kidney injury incidence is lower in coronary artery bypass grafting (CABG) patients (19%) compared to those undergoing valve surgery (27.5%) or aortic surgery (29.0%).

Our study has several limitations. Firstly, our study did not stratify patients by surgical type, limiting comparisons of cardiac surgery-associated acute kidney injury incidence, mortality rates, and lengths of stay across procedures. Secondly, we did not include the treatment regimens of the study participants, leaving us unable to determine whether different medications could improve patient outcomes, potentially introducing bias in the results. This opens avenues for future research in this area.

The LAR index appears to be associated with the incidence and adverse outcomes of AKI following cardiac surgery. Patients who develop AKI post-cardiac surgery and have elevated LAR levels face higher in-hospital and ICU mortality rates. Our study highlights the previously unreported role of the LAR index as an independent risk factor for mortality in cardiac surgery-related AKI. Further large-scale studies are needed to determine whether identifying or intervening in patients with elevated LAR levels can positively impact clinical outcomes in this population.

Data Availability Statement

The publicly available datasets in this study can be found online. The names of the repository/repositories and accession number(s) can be found below: https://mimic-iv.mit.edu/. Further inquiries can be directed to the corresponding author.

Ethics Statement and consent to participate

The MIMIC-IV database was approved by the Massachusetts Institute of Technology (Cambridge, MA) and Beth Israel Deaconess Medical Center (Boston, MA), and consent was obtained for the original data collection.

Acknowledgements

Not applicable

Author Contributions

CW, XS and KC designed the work. CW and XS record and summarized the patient of MIMIC features. LW, SC and JG analyzed the rationality of whole statistical analysis. DL provided the database approval. All authors read and approved the final manuscript.

Funding

This study was supported by the Medical science research project of Hebei Province (Grant No.: 20200712).

Disclosure

All authors have no competing interests in this work.

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No competing interests reported.

supplementarymaterials.pdf

Lactate-to-albumin ratio index correlates with the occurrence and prognosis of acute kidney injury complicated by cardiac surgery

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Abstract

Background

Methods

Results

Conclusions

Figures

Introduction

Methods

Data source

Data extraction

Statistical Analysis

Results

Baseline Characteristics and Clinical Outcomes of Patients with AKI after Cardiac Surgery

Elevated LAR Associated with Increased Mortality in Post-Cardiac Surgery AKI Patients

Restricted Cubic Spline Analysis

Subgroup Analysis

Discussion

Conclusion

Declarations

References

Additional Declarations

Supplementary Files

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Version 1