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

The predictive value of the serum creatinine-to-albumin ratio (sCAR) and lactate dehydrogenase-to-albumin ratio (LAR) in sepsis-related persistent severe acute kidney injury

BACKGROUND/OBJECTIVES

Sepsis-related acute kidney injury (SA-AKI) is a severe condition characterized by high mortality rates. The utility of the sCAR (secrum creatinine/albumin) and LAR (Lactate dehydrogenase/albumin) as diagnostic markers for persistent severe SA-AKI remains unclear.

METHODS

We acquired training set data from the MIMIC-IV database and validation set data from the First Affiliated Hospital of Harbin Medical University. Logistic regression analysis was used to identify key predictors of persistent severe SA-AKI, considering factors such as sCAR, LAR, PAR (Platelet/albumin), BAR (BUN/albumin), and LAO (Lactic/albumin). Independent predictors, sCAR and LAR, were combined into a composite Log(sCAR)_Log(LAR) score, denoted as the Log(sCAR)_Log(LAR) score. Possible confounding factors were screened out by univariate logistic regression, and multivariable logistic regression was applied to evaluate the association of Log (sCAR) _Log (LAR) score with persistent severe sepsis and other secondary clinical outcomes. The ROC curve was utilized to obtain the best cutoff value of the Log(sCAR)_Log(LAR) score. The Kaplan-Meier curve was used to evaluate the prognosis predictive ability of the risk model.

RESULTS

Logistic regression analysis indicated that sCAR and LAR independently predicted persistent severe SA-AKI. This led to the creation of Log(sCAR)_Log(LAR) score on the base of logarithms of sCAR and LAR. ROC curve analysis showed that the Log(sCAR)_Log(LAR) score was more effective in predicting persistent severe SA-AKI (AUC = 0.71) than Log(sCAR) (AUC = 0.69), Log(LAR) (AUC = 0.65), SOFA score (AUC = 0.66) and Δ Scr (AUC = 0.70). Multivariate regression identified that the SOFA score, PT, ΔScr, Tbil, chronic liver disease, and Vasopressor use as independent risk factors for persistent severe SA-AKI (P < 0.05). A basic clinical prediction model was created using these variables, and its predictive ability, recognition capability, and clinical utility improved with the inclusion of the Log(sCAR)_Log(LAR) score. The model's predictive ability for secondary outcomes, such as renal replacement therapy (RRT), also improved with the addition of the Log(sCAR)_Log(LAR) score. The sensitivity analysis further corroborated the stability of the Log(sCAR)_Log(LAR) score in predicting persistent severe SA-AKI and secondary outcomes, such as RRT.

CONCLUSIONS

The Log(sCAR)_Log(LAR) score effectively predicted persistent severe SA-AKI, potentially aiding intensive care physicians in risk assessment.

Impact of low pneumoperitoneum on renal function and acute kidney injury biomarkers during robot-assisted radical prostatectomy (RARP): a randomised clinical trial

The objective of this study was to evaluate the effect of low pneumoperitoneum pressure (Pnp) on renal function and renal injury biomarkers during robot-assisted radical prostatectomy (RARP). A single-centre, triple-blinded, randomised clinical trial was conducted with 98 patients undergoing RARP, who were assigned to either standard Pnp of 12 mmHg or low Pnp of 7 mmHg. The primary outcome was urinary neutrophil gelatinase-associated lipocalin (u-NGAL), and several other kidney injury biomarkers were assessed as secondary outcomes. Acute kidney injury (AKI) was evaluated using the Kidney Disease Improving Global Outcomes (KDIGO) criteria, the gold standard method for defining AKI. The trial was registered on ClinicalTrials.gov (NCT04755452). Patients in the low Pnp group had significantly lower levels of u-NGAL (mean difference - 39.9, 95% CI - 73.7 to - 6.1, p = 0.02) compared to the standard Pnp group. No significant differences were observed for other urinary biomarkers. Interestingly, there was a significant difference in intraoperative urine production between the groups (low Pnp median: 200 mL, IQR: 100-325 vs. standard Pnp median: 100 mL, IQR: 50-200, p = 0.01). Similarly, total postoperative urine production also varied significantly (low Pnp median: 1325 mL, IQR: 1025-1800 vs. standard Pnp median: 1000 mL, IQR: 850-1287, p = 0.001). The occurrence of AKI, as defined by the KDIGO criteria, did not differ significantly between the groups. Low Pnp during RARP resulted in lower u-NGAL levels, suggesting a potential benefit in terms of reduced renal injury. However, the lack of a notable difference in AKI as defined by the KDIGO criteria indicates that the clinical significance of this finding may be limited. Further research is needed to validate and expand on these results, ultimately defining the optimal Pnp strategy for RARP and improving patient outcomes.

Clinical and subclinical acute kidney injury in children with mild-to-moderate COVID-19

BACKGROUND

Our aim was to identify acute kidney injury (AKI) and subacute kidney injury using both KDIGO criteria and urinary biomarkers in children with mild/moderate COVID-19.

METHODS

This cross-sectional study included 71 children who were hospitalized with a diagnosis of COVID-19 from 3 centers in Istanbul and 75 healthy children. We used a combination of functional (serum creatinine) and damage (NGAL, KIM-1, and IL-18) markers for the definition of AKI and subclinical AKI. Clinical and laboratory features were evaluated as predictors of AKI and subclinical AKI.

RESULTS

Patients had significantly higher levels of urinary biomarkers and urine albumin-creatinine ratio than healthy controls (p < 0.001). Twelve patients (16.9%) developed AKI based on KDIGO criteria, and 22 patients (31%) had subclinical AKI. AKI group had significantly higher values of neutrophil count on admission than both subclinical AKI and non-AKI groups (p < 0.05 for all). Neutrophil count was independently associated with the presence of AKI (p = 0.014).

CONCLUSIONS

This study reveals that even children with a mild or moderate disease course are at risk for AKI. Association between neutrophil count and AKI may point out the role of inflammation in the development of AKI.

IMPACT

The key message of our article is that not only children with severe disease but also children with mild or moderate disease have an increased risk for kidney injury due to COVID-19. Urinary biomarkers enable the diagnosis of a significant number of patients with subclinical AKI in patients without elevation in serum creatinine. Our findings reveal that patients with high neutrophil count may be more prone to develop AKI and should be followed up carefully. We conclude that even children with mild or moderate COVID-19 disease courses should be evaluated for AKI and subclinical AKI, which may improve patient outcomes.

The relationship between hyperchloremia and acute kidney injury in pediatric diabetic ketoacidosis and its impact on clinical outcomes

INTRODUCTION

Diabetic ketoacidosis (DKA) is characterized by hyperglycemia, ketogenesis, and increased anion gap metabolic acidosis. Such derangements are accompanied by volume depletion as well as electrolyte disturbances. Resuscitation using traditional saline in DKA patients can exacerbate electrolyte abnormalities, in particular the production of hyperchloremia. Severe hypovolemia can result in acute kidney injury (AKI). The link between hyperchloremia and AKI is controversial. This study aimed to assess the relationship between hyperchloremia and AKI in pediatric patients with DKA and its impacts on clinical outcomes.

METHODS

This cross-sectional study was conducted on 70 children with DKA admitted to the pediatric intensive care unit in which all patients were subjected to detailed medical history taking and full clinical examination. Daily assessment of Na, K, urea, creatinine, chloride, arterial blood gases, and albumin/creatinine ratio (ACR) was done. AKI was defined as pRIFLE stage I and F.

RESULTS

Hyperchloremia was detected in 65.7% of patients at admission and in 52.9% after 24 h (p = 0.17). AKI was documented in 28% of patients. At admission hyperchloremia was detected in 56% of patients without AKI versus 90% of patients with AKI (p = 0.007). After 24 h, hyperchloremia was detected in 48.4% patients without versus 100% of patients with AKI. Chloride was significantly positively correlated to duration of admission, creatinine, ACR, and negatively correlated to eGFR.

CONCLUSION

The development of AKI in patients with DKA was accompanied by hyperchloremia, increased time to DKA resolution, and longer hospital stay. A higher resolution version of the Graphical abstract is available as Supplementary information.

Perioperative albuminuria and clinical model to predict acute kidney injury in paediatric cardiac surgery

BACKGROUND

AKI is an important complication post cardiac surgery in children. An early diagnosis can help in mitigating complications and allow for prognostication. Urinary albumin:creatinine ratio (ACR) as a biomarker can provide a cheaper and more accessible AKI risk assessment and prediction. There is a paucity of paediatric literature regarding its utility.

METHODS

This was a prospective observational study, enrolling all children aged 1 month to 18 years, who underwent cardiac surgery, with use of cardiopulmonary bypass. Cohort was divided into groups < 2 years and ≥ 2 years for analyses to account for differences in physiological albumin excretion with age.

RESULTS

Of 143 children enrolled in the study, 36 developed AKI. In both age groups, the post-operative ACR was higher than pre-operative ACR among patients with and without AKI. In the group aged ≥ 2 years, the highest first post-operative ACR tertile (> 75.8 mg/g) predicted post-operative AKI after adjusting for clinical variables (adjusted RR, 11.71; 1.85-16.59). In the group aged < 2 years, the highest first post-operative ACR tertile (> 141.3 mg/g) predicted post-operative AKI in unadjusted analysis but not after adjusting for clinical variables (RR, 2.78; 0.70-6.65). For AKI risk prediction, AUC (95% CI) was highest after combining clinical model and pre-operative ACR for groups aged < 2 years [0.805 (0.713-0.896)] and ≥ 2 years [0.872 (0.772-0.973)].

CONCLUSIONS

This study provides evidence for use of albuminuria as a feasible biomarker in AKI prediction in children post cardiac surgery, especially when added to a clinical model. A higher resolution version of the Graphical abstract is available as Supplementary information.

Conceptual advances and evolving terminology in acute kidney disease

Over the past decade, new insights into epidemiology, pathophysiology and biomarkers have modified our understanding of acute kidney dysfunction and damage, and their association with subsequent chronic kidney disease. The concept of acute kidney injury (AKI), which has relied on established but nonetheless flawed biomarkers of solute clearance (serum creatinine levels and urinary output), has been challenged by the identification of novel biomarkers of tubular stress and/or damage. The expression of some of these novel biomarkers precedes changes in conventional biomarkers or can increase their predictive power, and might therefore enhance the clinical accuracy of the definition of AKI. In addition, the need to consider AKI recurrence, duration and progression to chronic kidney disease within the clinical and epidemiological framework of AKI led to the emergence of the concept of acute kidney disease. New definitions of acute syndromes of kidney impairment and injury are needed.

Acute Kidney Injury and Risk of CKD and Hypertension after Pediatric Cardiac Surgery

BACKGROUND AND OBJECTIVES

The association of AKI after pediatric cardiac surgery with long-term CKD and hypertension development is unclear. The study objectives were to determine whether AKI after pediatric cardiac surgery is associated with incident CKD and hypertension.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was a prospective cohort study of children of 1 month to 18 years old who were undergoing cardiac surgery at two tertiary care centers (Canada, United States). Participants were recruited before cardiac surgery and were followed during hospitalization and at 3, 12, 24, 36, and 48 months after discharge. Exposures were postoperative AKI, based on the Kidney Disease Improving Global Outcomes (KDIGO) definition, and age <2 years old at surgery. Outcomes and measures were CKD (low eGFR or albuminuria for age) and hypertension (per the 2017 American Academy of Pediatrics guidelines) at follow-up, with the composite outcome of CKD or hypertension.

RESULTS

Among 124 participants, 57 (46%) developed AKI. AKI versus non-AKI participants had a median (interquartile range) age of 8 (4.8-40.8) versus 46 (6.0-158.4) months, respectively, and higher preoperative eGFR. From the 3- to 48-month follow-up, the cohort prevalence of CKD was high (17%-20%); hypertension prevalence was also high (22%-30%). AKI was not significantly associated with the development of CKD throughout follow-up. AKI was associated with hypertension development at 12 months after discharge (adjusted relative risk, 2.16; 95% confidence interval, 1.18 to 3.95), but not at subsequent visits. Children aged <2 years old at surgery had a significantly higher prevalence of hypertension during follow-up than older children (40% versus 21% at 3-month follow-up; 32% versus 13% at 48-month follow-up).

CONCLUSIONS

CKD and hypertension burden in the 4 years after pediatric cardiac surgery is high. Young age at surgery, but not AKI, is associated with their development.

Early prediction of acute kidney injury in neonates with cardiac surgery

Background

Acute kidney injury (AKI) occurs in 42%–64% of the neonatal patients experiencing cardiac surgery, contributing to postoperative morbidity and mortality. Current diagnostic criteria, which are mainly based on serum creatinine and hourly urine output, are not sufficiently sensitive and precise to diagnose neonatal AKI promptly. The purpose of this review is to screen the recent literature, to summarize the novel and cost-effective biomarkers and approaches for neonatal AKI after cardiac surgery (CS-AKI), and to provide a possible research direction for future work.

Data sources

We searched PubMed for articles published before November 2019 with pertinent terms. Sixty-seven articles were found and screened. After excluding 48 records, 19 articles were enrolled for final analysis.

Results

Nineteen articles were enrolled, and 18 possible urinary biomarkers were identified and evaluated for their ability to diagnose CS-AKI. Urinary neutrophil gelatinase-associated lipocalin (uNGAL), serum cystatin C (sCys), urinary human kidney injury molecule-1 (uKIM-1), urinary liver fatty acid-binding protein (uL-FABP) and interleukin-18 (uIL-18) were the most frequently described as the early predictors of neonatal CS-AKI.

Conclusions

Neonates are vulnerable to CS-AKI. UNGAL, sCys, uL-FABP, uKIM-1 and uIL-18 are potential biomarkers for early prediction of neonatal CS-AKI. Renal regional oxygen saturation by near-infrared spectroscopy is a non-invasive approach for early identification of neonatal AKI. Further work should focus on exploring a sensitive and specific combined diagnostic model that includes novel biomarkers and other complementary methods.

Glyphosate exposures and kidney injury biomarkers in infants and young children

The goal of this study was to assess biomarkers of exposure to glyphosate and assess potential associations with renal function in children. Glyphosate is used ubiquitously in agriculture worldwide. While previous studies have indicated that glyphosate may have nephrotoxic effects, few have examined potential effects on kidney function in children. We leveraged three cohorts across different phases of child development and measured urinary levels of glyphosate. We evaluated associations of glyphosate with three biomarkers of kidney injury: albuminuria (ACR), neutrophil gelatinase-associated lipocalin (NGAL), and kidney injury marker 1 (KIM-1). Multivariable regression analyses examined associations of glyphosate with kidney injury biomarkers controlling for covariates. We identified glyphosate in 11.1% of the total participants. The herbicide was detected more frequently in the neonate population (30%). Multivariable regression models failed to identify significant associations of log-transformed glyphosate with any of the kidney injury biomarkers, controlling for covariates age, sex, and maternal education. While we confirm detectability of glyphosate in children's urine at various ages and stages of life, there is no evidence in this study for renal injury in children exposed to low levels of glyphosate. Further studies of larger sample size are indicated to better understand putative deleterious effects of the herbicide after different levels of exposure.

The Japanese clinical practice guideline for acute kidney injury 2016

Acute kidney injury (AKI) is a syndrome which has a broad range of etiologic factors depending on different clinical settings. Because AKI has significant impacts on prognosis in any clinical settings, early detection and intervention is necessary to improve the outcomes of AKI patients. This clinical guideline for AKI was developed by a multidisciplinary approach with nephrology, intensive care medicine, blood purification, and pediatrics. Of note, clinical practice for AKI management which was widely performed in Japan was also evaluated with comprehensive literature search.

Utility of urinary tubular markers for monitoring chronic tubulointerstitial injury after ischemia-reperfusion

AIM

The aim of this study was to elucidate whether urinary tubular markers during the chronic phase of acute kidney injury (AKI) are associated with chronic tubulointerstitial damage.

METHODS

Male human L-type fatty acid binding protein (L-FABP) chromosomal transgenic (Tg) mice underwent ischaemic reperfusion (I/R) injury via renal pedicle clamping for either 10 min or 20 min. Contralateral nephrectomy was performed at the time of tissue reperfusion. The kidneys were analyzed 20 days after the last I/R.

RESULTS

Serum creatinine levels 20 days post-I/R were significantly higher in the 20 min I/R than in the 10 min I/R and control groups and were similar between the 10 min I/R and control groups. The degree of tubulointerstitial damage 20 days post-I/R was significantly more severe in the 20 min I/R than in the 10 min I/R and control groups, as well as in the 10 min I/R than in the control group. Urinary levels of human L-FABP, albumin, and kidney injury molecule-1 (KIM-1) 20 days post-I/R were significantly higher in the 20 min I/R than in the control group, whereas urinary L-FABP was significantly higher in the 10 min I/R than in the control group. Conversely, urinary neutrophil gelatinase-associated lipocalin levels did not significantly differ between the three groups. Finally, the urinary levels of human L-FABP, albumin, and KIM-1 levels 20 days post-I/R were significantly correlated with the degree of renal damage.

CONCLUSIONS

Urinary levels of human L-FABP, albumin and, KIM-1 may be useful for monitoring AKI-to-CKD transition in clinical practice.

The Japanese Clinical Practice Guideline for acute kidney injury 2016

Acute kidney injury (AKI) is a syndrome which has a broad range of etiologic factors depending on different clinical settings. Because AKI has significant impacts on prognosis in any clinical settings, early detection and intervention are necessary to improve the outcomes of AKI patients. This clinical guideline for AKI was developed by a multidisciplinary approach with nephrology, intensive care medicine, blood purification, and pediatrics. Of note, clinical practice for AKI management which was widely performed in Japan was also evaluated with comprehensive literature search.

Biomarkers of AKI Progression after Pediatric Cardiac Surgery

Background As children progress to higher stages of AKI, the risk for adverse outcomes dramatically increases. No reliable methods exist to predict AKI progression in hospitalized children. To determine if biomarkers of inflammation and kidney injury can predict AKI progression, we conducted a three-center prospective cohort study of children undergoing cardiopulmonary bypass.Methods On the first day of serum creatinine-defined AKI, we measured urine biomarkers (neutrophil gelatinase-associated lipocalin [NGAL], IL-18, kidney injury molecule 1, liver fatty acid binding protein [L-FABP], albumin, and cystatin C) and plasma biomarkers (IFN, IL-1, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-13, TNF-α, NGAL, and cystatin C). We defined AKI progression as a worsening of AKI stage or persisting stage 3 AKI (≥2 consecutive days).Results In all, 176 of 408 (43%) children developed postoperative AKI. Among the children with AKI, we diagnosed stages 1, 2, and 3 AKI in 145 (82.5%), 25 (14%), and six (3.5%) children, respectively, on the first day of AKI; 28 (7%) children had AKI progression. On the first day of AKI, nine of 17 biomarkers were significantly higher in patients with than without AKI progression. Urine L-FABP (among injury biomarkers) and plasma IL-8 (among inflammatory biomarkers) had the highest discrimination for AKI progression: optimism-corrected area under the curve, 0.70; 95% confidence interval, 0.58 to 0.81 and optimism-corrected area under the curve, 0.80; 95% confidence interval, 0.69 to 0.91, respectively.Conclusions If validated in additional cohorts, plasma IL-8 could be used to improve clinical care and guide enrollment in therapeutic trials of AKI.

Pre-admission proteinuria impacts risk of non-recovery after dialysis-requiring acute kidney injury

Renal recovery after dialysis-requiring acute kidney injury (AKI-D) is an important clinical and patient-centered outcome. Here we examined whether the pre-admission proteinuria level independently influences risk for non-recovery after AKI-D in a community-based population. All adult members of Kaiser Permanente Northern California who experienced AKI-D between January 1, 2009 and September 30, 2015 were included. Pre-admission proteinuria levels were determined by dipstick up to four years before the AKI-D hospitalization and the outcome was renal recovery (survival and dialysis-independence four weeks and more) at 90 days after initiation of renal replacement therapy. We used multivariable logistic regression to adjust for baseline estimated glomerular filtration rate (eGFR), age, sex, ethnicity, short-term predicted risk of death, comorbidities, and medication use. Among 5,347 adults with AKI-D, the mean age was 66 years, 59% were men, and 50% were white. Compared with negative/trace proteinuria, the adjusted odds ratios for non-recovery (continued dialysis-dependence or death) were 1.47 (95% confidence interval 1.19-1.82) for 1+ proteinuria and 1.92 (1.54-2.38) for 2+ or more proteinuria. Among survivors, the crude probability of recovery ranged from 83% for negative/trace proteinuria with baseline eGFR over 60 mL/min/1.73m² to 25% for 2+ or more proteinuria with eGFR 15-29 mL/min/1.73m². Thus, the pre-AKI-D level of proteinuria is a graded, independent risk factor for non-recovery and helps to improve short-term risk stratification for patients with AKI-D.

Urine biomarkers of acute kidney injury in noncritically ill, hospitalized children treated with chemotherapy

BACKGROUND

Cisplatin (Cis), carboplatin (Carb), and ifosfamide (Ifos) are common nephrotoxic chemotherapies. Biomarkers of tubular injury may allow for early acute kidney injury (AKI) diagnosis.

PROCEDURE

We performed a two-center (Canada, United States) pilot study to prospectively measure serum creatinine (SCr), urine neutrophil gelatinase-associated lipocalin (NGAL), and interleukin-18 (IL-18) in children receiving Cis/Carb (27 episodes), Ifos (30 episodes), and in 15 hospitalized, nonchemotherapy patients. We defined AKI using the Kidney Disease Improving Global Outcomes (KDIGO) definition. We compared postchemotherapy infusion NGAL and IL-18 concentrations (immediate postdose to 3 days later) to pre-infusion concentrations. We calculated area under the receiver operating characteristic curve (AUC) for postinfusion biomarkers to discriminate for AKI.

RESULTS

Prechemotherapy infusion NGAL and IL-18 concentrations were not higher than nonchemotherapy control concentrations. Increasing chemotherapy dose was associated with increasing postinfusion (0-4 hr after infusion) NGAL (P < 0.05). Post-Ifos, immediate postdose, and daily postdose NGAL and IL-18 were significantly higher than pre-infusion biomarker concentrations (P < 0.05), during AKI episodes. NGAL and IL-18 did not rise significantly after Cis-Carb infusion, relative to predose concentrations (P > 0.05). NGAL and IL-18 measured immediately after Ifos infusion discriminated for AKI with AUCs is 0.80 (standard error = 0.13) and 0.73 (standard error = 0.16), respectively. NGAL and IL-18 were not diagnostic of Cis-Carb-associated AKI. When AUCs were adjusted for age, all biomarker AUCs (Cis-Carb and Ifos) improved.

CONCLUSION

Urine NGAL and IL-18 show promise as early AKI diagnostic tests in children treated with ifosfamide and may have a potential role in drug toxicity monitoring.

Biomarkers for Diagnosis and Prognosis of AKI in Children: One Size Does Not Fit All

Pediatric AKI has become a significant health concern due to its rising incidence and association with adverse outcomes. Because of the limitations of serum creatinine, ongoing research has evaluated multiple novel biomarkers for the early detection of AKI. Identifying biomarkers that precede changes in serum creatinine is vital, because these biomarkers provide opportunities to improve outcomes through early diagnosis and timely disease management. In this review, we discuss salient findings on 16 candidate biomarkers and their association with AKI. We explore the differences in biomarker distribution by age and discuss why adult biomarker research findings cannot be directly extrapolated to children. With future research, more consideration needs to be given to how the maturing kidney affects biomarker levels and how we interpret biomarker performance in children. A comprehensive approach using age-specific biomarker reference ranges is required to develop pediatric biomarkers and improve outcomes for children with kidney disease.

Interleukin-8 and Tumor Necrosis Factor Predict Acute Kidney Injury After Pediatric Cardiac Surgery

BACKGROUND

Inflammation is a key component of both acute kidney injury (AKI) and response to cardiopulmonary bypass. Because AKI poses risks to children after cardiac surgery, we investigated the value of inflammatory biomarkers interleukin-8 (IL-8) and tumor necrosis factor alpha (TNFα) for predicting AKI and other complications.

METHODS

We enrolled 412 children between the ages of 1 month and 18 years undergoing cardiopulmonary bypass for cardiac surgery. We collected blood both preoperatively and postoperatively (within 6 hours post-surgery) and measured plasma IL-8 and TNFα.

RESULTS

IL-8 and TNFα did not predict AKI in children <2 years, but were strongly associated with AKI in children ≥2 years. There were significant associations between biomarker levels and age (<2 or ≥2 years). In children ≥2 years, patients in the highest tertile of preoperative IL-8 and postoperative TNFα had 4.9-fold (95% CI: 1.8-13.2) and 3.3-fold (95% CI: 1.2-9.0) higher odds of AKI compared with those in the lowest tertile. Children <2 years with higher biomarker levels also had higher odds of AKI, but the difference was not significant. We also found that postoperative TNFα levels were significantly higher in patients with longer hospital stays, and that both postoperative IL-8 and TNFα levels were significantly higher in patients with longer ventilation lengths. There was no evidence that biomarker levels mediated the association between AKI and length of ventilation; they appear to be independent predictors.

CONCLUSIONS

Preoperative IL-8 and postoperative TNFα are significantly associated with higher odds of AKI and greater lengths of hospital stays and ventilator use in children 2 years and older.

AKI after pediatric cardiac surgery for congenital heart diseases-recent developments in diagnostic criteria and early diagnosis by biomarkers

Background

Acute kidney injury (AKI) after cardiac surgery in children with congenital heart disease is a common complication. AKI is also associated with high morbidity and mortality. The Kidney Diseases Improving Global Outcomes (KDIGO) criteria for AKI classification are now widely used for the definition of AKI. It is noteworthy that a statement about children was added to the criteria. Many studies aimed at finding useful biomarkers are now being performed by using these criteria. Clinicians should be aware of the recent progress in understanding AKI in children.

Main contents

Unlike adult patients, young age is one of the major risk factors for AKI in pediatric cardiac surgery. The mechanism of the development of AKI in children might be different from that in adults because the surgical procedure and CPB technique in pediatric patients are greatly different from those in adult patients.

There are many biomarkers for early detection of AKI, and some of them are widely used in hospitals. One of the major benefits of such biomarkers is the rapidness of expression for detecting increases in their expression levels. Neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, cystatin C, and albumin have been investigated in some studies, and the usefulness of these biomarkers for detection of AKI and diagnosis of disease severity has been shown.

Although there are many interventions for preventing and treating AKI after cardiac surgery in children, there is still no specific effective treatment. Peritoneal dialysis is effective for only maintaining a negative fluid balance early after cardiac surgery. The long-term prognosis of AKI is an issue of interest. Although mortality and morbidity of AKI in the acute phase of disease remain high, the long-term condition in pediatric patients is relatively acceptable unlike in adults.

Conclusions

KDIGO criteria are advocated as a diagnostic tool for common perception. Early recognition and intervention for AKI can be achieved by using several biomarkers. Further studies are needed to establish effective treatment for AKI.

Nephrotoxicity-induced proteinuria increases biomarker diagnostic thresholds in acute kidney injury

BACKGROUND

Paraquat ingestion is frequently fatal. While biomarkers of kidney damage increase during paraquat-induced acute kidney injury (AKI), significant concurrent proteinuria may alter diagnostic thresholds for diagnosis and prognosis to an unknown extent. This study evaluated the effect of albuminuria on biomarker cutoffs for diagnosis and outcome prediction.

METHODS

This was a multi-centre prospective clinical study of patients following acute paraquat self-poisoning in 5 Sri Lankan hospitals. Biomarker concentrations were quantified using ELISA and microbead assays and correlated with urinary albumin. Functional-AKI was defined by the Acute Kidney Injury Network serum creatinine definition and alternatively by a ≥50% increase in serum cystatin C. Albuminuria was defined as albumin-creatinine ratio >30 mg/g. The study outcomes were compared with a retrospective analysis of a pre-clinical study of paraquat-induced nephrotoxicity with appropriate controls.

RESULTS

Albuminuria was detected in 34 of 50 patients, and increased with functional-AKI severity. The concentrations of uNGAL, uCysC, uClusterin, uβ2M, and uKIM-1 were higher in albuminuric compared to non-albuminuric patients (p < 0.001). Albuminuria correlated with biomarker concentration (r > 0.6, p < 0.01) and was associated with death (p = 0.006). Optimal biomarker cutoffs for prediction of death were higher in the albuminuric group. Similar outcomes with more detailed analysis were obtained in experimental paraquat nephrotoxicity.

CONCLUSION

Albuminuria was associated with paraquat-induced nephrotoxicity and increased excretion of low-molecular weight protein biomarkers. AKI biomarker cutoffs for diagnosis, outcome prediction and AKI stratification increased in the presence of albuminuria. This may lead to over-diagnosis of AKI in conditions independently associated with proteinuria.

Evaluation of clinically available renal biomarkers in critically ill adults: a prospective multicenter observational study

BACKGROUND

Although serum cystatin C (sCysC), urinary N-acetyl-β-D-glucosaminidase (uNAG), and urinary albumin/creatinine ratio (uACR) are clinically available, their optimal combination for acute kidney injury (AKI) detection and prognosis prediction remains unclear. We aimed to assess the discriminative abilities of these biomarkers and their possible combinations for AKI detection and intensive care unit (ICU) mortality prediction in critically ill adults.

METHODS

A multicenter, prospective observational study was conducted in mixed medical-surgical ICUs at three tertiary care hospitals. One thousand eighty-four adult critically ill patients admitted to the ICUs were studied. We assessed the use of individual biomarkers (sCysC, uNAG, and uACR) measured at ICU admission and their combinations with regard to AKI detection and prognosis prediction.

RESULTS

AUC-ROCs for sCysC, uNAG, and uACR were calculated for total AKI (0.738, 0.650, and 0.683, respectively), severe AKI (0.839, 0.706, and 0.771, respectively), and ICU mortality (0.727, 0.793, and 0.777, respectively). The panel of sCysC plus uNAG detected total and severe AKI with significantly higher accuracy than either individual biomarkers or the other two panels (uNAG plus uACR or sCysC plus uACR). For detecting total AKI, severe AKI, and ICU mortality at ICU admission, this panel yielded AUC-ROCs of 0.756, 0.863, and 0.811, respectively; positive predictive values of 0.71, 0.31, and 0.17, respectively; and negative predictive values of 0.81, 0.97, and 0.98, respectively. Moreover, this panel significantly contributed to the accuracy of the clinical models for AKI detection and ICU mortality prediction, as measured by the AUC-ROC, continuous net reclassification index, and incremental discrimination improvement index. The comparable performance of this panel was further confirmed with bootstrap internal validation.

CONCLUSIONS

The combination of a functional marker (sCysC) and a tubular damage marker (uNAG) revealed significantly superior discriminative performance for AKI detection and yielded additional prognostic information on ICU mortality.

Longitudinal patterns of urine biomarkers in infants across gestational ages

BACKGROUND

Urinary biomarkers may be indicators of acute kidney injury (AKI), although little is known of their developmental characteristics in healthy neonates across a full range of gestational age (GA). The purpose of this study was to examine patterns of urinary biomarkers across GA groups from birth to 3 months of age.

METHODS

Fifty-two infants ranging from 24 to 41 weeks' GA had urine assayed from birth through 3 months of age for 7 biomarkers including albumin (ALB), beta-2-microglobulin (B2M), cystatin-C (CysC), epidermal growth factor (EGF), neutrophil-gelatinase-associated lipocalin (NGAL), osteopontin (OPN), and uromodulin (UMOD).

RESULTS

Of the seven urinary biomarkers, EGF and UMOD increased while others decreased with advancing GA. By 3 months of age, EGF and UMOD had increased in preterm infants to levels similar to those of term infants. UMOD/ml and EGF/ml appeared to be predominantly developmental biomarkers distinguishing estimated glomerular filtration rate (GFR) <30 ml/min/1.73 m(2) with receiver operator characteristic area under the curve (ROC-AUC) of 0.82; p = 0.002. When factored by urine creatinine CysC/cr + ALB/cr were the most significant functional markers with AUC = 0.79; p = 0.004; sensitivity 96 %; specificity 58 %.

CONCLUSIONS

Among healthy neonates, urinary biomarkers vary with GA. These data support the use of urinary biomarkers in the assessment of normal kidney development in the absence of injury.

Renoprotective effect of the xanthine oxidoreductase inhibitor topiroxostat on adenine-induced renal injury

The aim of the present study was to reveal the effect of a xanthine oxidoreductase (XOR) inhibitor, topiroxostat (Top), compared with another inhibitor, febuxostat (Feb), in an adenine-induced renal injury model. We used human liver-type fatty acid-binding protein (L-FABP) chromosomal transgenic mice, and urinary L-FABP, a biomarker of tubulointerstitial damage, was used to evaluate tubulointerstitial damage. Male transgenic mice ( n = 24) were fed a 0.2% (wt/wt) adenine-containing diet. Two weeks after the start of this diet, renal dysfunction was confirmed, and the mice were divided into the following four groups: the adenine group was given only the diet containing adenine, and the Feb, high-dose Top (Top-H), and low-dose Top (Top-L) groups were given diets containing Feb (3 mg/kg), Top-H (3 mg/kg), and Top-L (1 mg/kg) in addition to adenine for another 2 wk. After withdrawal of the adenine diet, each medication was continued for 2 wk. Serum creatinine levels, the degree of macrophage infiltration, tubulointerstitial damage, renal fibrosis, urinary 15-F2t-isoprostane levels, and renal XOR activity were significantly attenuated in the kidneys of the Feb, Top-L, and Top-H groups compared with the adenine group. Serum creatinine levels in the Top-L and Top-H groups as well as renal XOR in the Top-H group were significantly lower than those in the Feb group. Urinary excretion of L-FABP in both the Top-H and Top-L groups was significantly lower than in the adenine and Feb groups. In conclusion, Top attenuated renal damage in an adenine-induced renal injury model.

Are We Overdiagnosing Acute Kidney Injury in Pediatric Patients Following Cardiac Surgery?

BACKGROUND

The use of two diagnostic criteria in the current literature has led to some degree of ambiguity in the precise diagnosis of acute kidney injury in pediatric patients undergoing surgery for congenital heart disease. This study aims to determine which criteria is the most accurate diagnostic indicator of acute kidney injury and determine whether the incidence is being overestimated based on the current criteria.

METHODS

This retrospective study consisted of 389 patients with congenital heart disease from birth to 18 years, who underwent cardiac surgery. The statistical tests conducted were the student t test and chi-square test. Outcomes measured included hospital length of stay, duration of mechanical ventilation, and mortality.

RESULTS

The incidence rate of acute kidney injury diagnosed by the pediatric Risk, Injury, Failure, Loss, and End-Stage Renal Disease (RIFLE) criterion was 56% compared to 24.4% for the Acute Kidney Injury Network criterion. The pediatric RIFLE criterion consists of the following subsets: risk, injury, failure, loss, and end-stage renal disease. Patients classified in the "risk" subset of the pediatric RIFLE criterion who failed to meet Acute Kidney Injury Network criterion were compared to patients without acute kidney injury. Comparison of intensive care unit outcomes between these groups lacked statistical significance for all variables except the duration of mechanical ventilation postoperatively.

CONCLUSION

Although recent research in this field identified the pediatric RIFLE criterion as the most sensitive indicator of acute kidney injury, the results of this study suggest the pediatric RIFLE criterion overestimates acute kidney injury incidence and that the Acute Kidney Injury Network criterion is the more accurate diagnostic indicator.

Increase in urinary markers during the acute phase reflects the degree of chronic tubulointerstitial injury after ischemia-reperfusion renal injury

CONTEXT

Acute kidney injury (AKI) could lead to progressive chronic kidney disease (CKD).

OBJECTIVES

To demonstrate that urinary markers in AKI are associated with the degree of persistent renal injury.

MATERIAL AND METHODS

Human L-FABP chromosomal transgenic (T_g) mice were subjected to ischemia-reperfusion (I/R) clamping renal pedicle for 20 min or 30 min. Kidneys were obtained at one and 40 days after I/R.

RESULTS

Urinary L-FABP, NGAL, Kim-1 and albumin levels increased during the acute phase and were significantly correlated with the degree of tubulointerstitial fibrosis during the chronic phase.

DISCUSSION AND CONCLUSION

These markers could detect higher risk of progression to CKD.

Association of Pre-Operative Albuminuria with Post-Operative Outcomes after Coronary Artery Bypass Grafting

The effect on post-operative outcomes after coronary artery bypass graft(CABG) surgery is not clear. Among 17,812 patients who underwent CABG during October 1,2006-September 28,2012 in any Department of US Veterans Affairs(VA) hospital, we identified 5,968 with available preoperative urine albumin-creatinine ratio(UACR) measurements. We examined the association of UACR<30, 30–299 and >=300 mg/g with 30/90/180/365-day and overall all-cause mortality, and hospitalization length >10 days, and with acute kidney injury(AKI). Mean ± SD baseline age and eGFR were 66 ± 8 years and 77 ± 19 ml/min/1.73 m², respectively. 788 patients(13.2%) died during a median follow-up of 3.2 years, and 26.8% patients developed AKI(23.1%-Stage 1; 2.9%-Stage 2; 0.8%-Stage 3) within 30 days of CABG. The median lengths of stay were 8 days(IQR: 6–13 days), 10 days(IQR: 7–14 days) and 12 days(IQR: 8–19 days) for groups with UACR < 30 mg/g, 30–299 mg/g and ≥300 mg/g, respectively. Higher UACR conferred 72 to 85% higher 90-, 180-, and 365-day mortality compared to UACR<30 mg/g (odds ratio and 95% confidence interval for UACR≥300 vs. <30 mg/g: 1.72(1.01–2.95); 1.85(1.14–3.01); 1.74(1.15–2.61), respectively). Higher UACR was also associated with significantly longer hospitalizations and higher incidence of all stages of AKI. Higher UACR is associated with significantly higher odds of mortality, longer post-CABG hospitalization, and higher AKI incidence.

AKI associated with cardiac surgery

Approximately 18% of patients undergoing cardiac surgery experience AKI (on the basis of modern standardized definitions of AKI), and approximately 2%-6% will require hemodialysis. The development of AKI after cardiac surgery portends poor short- and long-term prognoses, with those developing RIFLE failure or AKI Network stage III having an almost 2-fold increase in the risk of death. AKI is caused by a variety of factors, including nephrotoxins, hypoxia, mechanical trauma, inflammation, cardiopulmonary bypass, and hemodynamic instability, and it may be affected by the clinician's choice of fluids and vasoactive agents as well as the transfusion strategy used. The risk of AKI may be ameliorated by avoidance of nephrotoxins, achievement of adequate glucose control preoperatively, and use of goal-directed therapy hemodynamic strategies. Remote ischemic preconditioning is an exciting future strategy, but more work is needed before widespread implementation. Unfortunately, there are no pharmacologic agents known to reduce the risk of AKI or treat established AKI.

Proteomics in acute kidney injury--current status and future promise

Pediatric acute kidney injury (AKI) is associated with increased morbidity, mortality and associated healthcare costs. Unfortunately, there are currently no effective therapies available, and this has been attributed in part to the late diagnosis of AKI. Therefore, significant efforts have been made to develop early diagnostic tools for AKI in the hope that early identification of renal injury will allow for effective therapeutic intervention. Different transcriptomic, proteomic and metabolomic technologies offer unbiased approaches to identifying novel biomarkers of AKI. This review will provide an overview of non-invasive pediatric AKI biomarkers. It will focus on unbiased technologies by using examples of biomarkers identified with "-omic" technologies and different methodological and implementation challenges will be highlighted. Finally, emerging proteomic techniques that may be applicable to biomarker discovery will be presented. Ultimately, the development of novel biomarkers of AKI may lead to the early diagnosis and effective therapeutic intervention of AKI to improve patient outcomes.

A basic science view of acute kidney injury biomarkers

Over the last decade, significant progress has been made in the identification and validation of novel biomarkers as well as refinements in the use of serum creatinine as a marker of kidney function. These advances have taken advantage of laboratory investigations, which have identified these novel molecules that serve important biological functions in the pathogenesis of acute kidney injury (AKI). As we advance and validate these markers for clinical studies in AKI, we recognize that they serve not only to improve our understanding of AKI, but they could also serve as potential targets for the treatment of AKI. This review will underscore the biological basis of specific biomarkers that will contribute to the advancement in the treatment and outcomes of AKI.

Neutrophil gelatinase-associated lipocalin and albuminuria as predictors of acute kidney injury in patients treated with goal-directed haemodynamic therapy after major abdominal surgery

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL) is emerging as a new biomarker for the early identification of acute kidney injury (AKI). There is also increasing evidence of an association between urinary albumin/creatinine ratio (ACR) and AKI. The primary aim of this study was to evaluate the clinical utility of these biomarkers to predict AKI in a population of perioperative patients treated with goal-directed haemodynamic therapy (GDHT). Secondary aims were to examine NGAL and ACR as sensitive biomarkers to detect the effects of GDHT and to investigate the association of these biomarkers with secondary outcomes.

METHODS

Urine was obtained from 109 patients admitted to a critical care unit following major abdominal surgery. Patients were treated with intravenous fluid, GDHT with intravenous fluid or GDHT with intravenous fluid and dopexamine. Urine was collected preoperatively, and at times 0, 8 and 24 h postoperatively and outcome monitored for 28 days.

RESULTS

There were no significant differences in NGAL or ACR concentrations between the cohorts treated with GDHT compared to standard care. However, both biomarker concentrations rose significantly in all cohorts over the time points. There were no significant differences in NGAL observed between patients who developed AKI and those who did not. However, there were significantly higher ACR preoperatively in patients who developed AKI. There were higher NGAL concentrations in patients who developed an infection and who died.

CONCLUSIONS

NGAL has a poor predictive role in evaluating AKI in this clinical setting. Preoperative ACR may have a role as an AKI marker.

Preoperative prediction of acute kidney injury--from clinical scores to biomarkers

Early acute kidney injury (AKI) diagnosis in critically ill children has been an important recent research focus because of the known association of AKI with poor outcomes and the requirement of early intervention to mitigate negative effects of AKI. In children having surgery, the preoperative period offers a unique opportunity to predict postoperative acute kidney injury (AKI), well before AKI occurs. Pediatric AKI epidemiologic studies have begun to identify which preoperative factors may predict development of postoperative cardiac surgery. Using these clinical risk factors, it may be possible to derive preoperative clinical risk scores and improve upon our ability to risk-stratify children into AKI treatment trials, pre-emptively provide conservative renal injury prevention strategies, and ultimately improve patient outcomes. Developing risk scores requires rigorous methodology and validation before widespread use. There is little information currently on the use of preoperative biological or physiological biomarkers to predict postoperative AKI, representing an important area of future research. This review will provide an overview of methodology of preoperative risk score development, discuss pediatric-specific issues around deriving such risk scores, including the combination of preoperative clinical and biologic biomarkers for AKI prediction, and suggest future research avenues.

Clinical utility of biomarkers of AKI in cardiac surgery and critical illness

AKI is a common and serious complication that is associated with several adverse outcomes in hospitalized patients. The past several years have seen a large number of multicenter investigations of biomarkers of AKI in the setting of cardiac surgery and critical illness. This review summarizes these biomarker results to identify applications for clinical use. The Translational Research Investigating Biomarker Endpoints in AKI (TRIBE-AKI) study showed that blood and urine biomarkers measured preoperatively, immediately postoperatively, and at the time of the clinical increase in serum creatinine in the setting of cardiac surgery all had the ability to improve patient risk stratification for a variety of important clinical end points. Analyses of biomarkers concentrations from the Acute Respiratory Distress Syndrome Network, EARLY ARF, and other studies of critically ill subjects have similarly shown that biomarkers measured early in the clinical course can forecast the development of AKI and need for renal replacement therapy as well as inpatient mortality. Although biomarkers have informed the diagnosis, prognosis, and treatment of AKI and are inching closer to clinical application, large multicenter interventional clinical trials to prevent AKI using biomarkers should continue to be an active area of clinical investigation.

Chronic kidney disease following acute kidney injury-risk and outcomes

In the past two decades, a substantial increase in the incidence of acute kidney injury (AKI) and kidney injury requiring dialysis has occurred in North America. This increase has coincided with an increase in the incidence of end-stage renal disease (ESRD), which has exceeded that expected based upon the prevalence of chronic kidney disease (CKD). In order to better understand the association between these conditions, there has been a proliferation of studies that have examined the risks of incident and progressive CKD following AKI. Animal studies have shown that failed differentiation of epithelial cells following renal ischaemia-reperfusion injury might lead to tubulointerstitial fibrosis, supporting a biological mechanism linking AKI and CKD. Strong and consistent associations between AKI and incident CKD, progression of CKD and incident ESRD have also been shown in epidemiological studies. In this Review, we summarize the wealth of available data on the relationship between AKI and CKD, and discuss the implications of these findings for the long-term clinical management of patients following AKI. We also identify areas of active investigation and future directions for research.