Risk Stratification for Acute Kidney Injury: Are Biomarkers Enough?

Evaluation of risk stratification for acute kidney injury: a comparative analysis of EKFC, 2009 and 2021 CKD-EPI glomerular filtration estimating equations

BACKGROUND

The adoption of the 2021 CKD-EPIcr equation for glomerular filtration rate (GFR) estimation provided a race-free eGFR calculation. However, the discriminative performance for AKI risk has been rarely validated. We aimed to evaluate the differences in acute kidney injury (AKI) prediction or reclassification power according to the three eGFR equations.

METHODS

We performed a retrospective observational study within a tertiary hospital from 2011 to 2021. Acute kidney injury was defined according to KDIGO serum creatinine criteria. Glomerular filtration rate estimates were calculated by three GFR estimating equations: 2009 and 2021 CKD-EPIcr, and EKFC. In three equations, AKI prediction performance was evaluated with area under receiver operator curves (AUROC) and reclassification power was evaluated with net reclassification improvement analysis.

RESULTS

A total of 187,139 individuals, including 27,447 (14.7%) AKI and 159,692 (85.3%) controls, were enrolled. In the multivariable regression prediction model, the 2009 CKD-EPIcr model (continuous eGFR model 2, 0.7583 [0.755-0.7617]) showed superior performance in AKI prediction to the 2021 CKD-EPIcr (0.7564 [0.7531-0.7597], < 0.001) or EKFC model in AUROC (0.7577 [0.7543-0.761], < 0.001). Moreover, in reclassification of AKI, the 2021 CKD-EPIcr and EKFC models showed a worse classification performance than the 2009 CKD-EPIcr model. (- 7.24 [- 8.21-- 6.21], - 2.38 [- 2.72-- 1.97]).

CONCLUSION

Regarding AKI risk stratification, the 2009 CKD-EPIcr equation showed better discriminative performance compared to the 2021 CKD-EPIcr equation in the study population.

Early and late acute kidney injury: temporal profile in the critically ill pediatric patient

Background

Increasing AKI diagnosis precision to refine the understanding of associated epidemiology and outcomes is a focus of recent critical care nephrology research. Timing of onset of acute kidney injury (AKI) during pediatric critical illness and impact on outcomes has not been fully explored.

Methods

This was a secondary analysis of the Assessment of Worldwide Acute Kidney Injury, Renal Angina and Epidemiology (AWARE) database. AKI was defined as per Kidney Disease: Improving Global Outcomes criteria. Early AKI was defined as diagnosed at ≤48 h after intensive care unit (ICU) admission, with any diagnosis >48 h denoted as late AKI. Transient AKI was defined as return to baseline serum creatinine ≤48 h of onset, and those without recovery fell into the persistent category. A second incidence of AKI ≥48 h after recovery was denoted as recurrent. Patients were subsequently sorted into distinct phenotypes as early-transient, late-transient, early-persistent, late-persistent and recurrent. Primary outcome was major adverse kidney events (MAKE) at 28 days (MAKE28) or at study exit, with secondary outcomes including AKI-free days, ICU length of stay and inpatient renal replacement therapy.

Results

A total of 1262 patients had AKI and were included. Overall mortality rate was 6.4% (n = 81), with 34.2% (n = 432) fulfilling at least one MAKE28 criteria. The majority of patients fell in the early-transient cohort (n = 704, 55.8%). The early-persistent phenotype had the highest odds of MAKE28 (odds ratio 7.84, 95% confidence interval 5.45–11.3), and the highest mortality rate (18.8%). Oncologic and nephrologic/urologic comorbidities at AKI diagnosis were associated with MAKE28.

Conclusion

Temporal nature and trajectory of AKI during a critical care course are significantly associated with patient outcomes, with several subtypes at higher risk for poorer outcomes. Stratification of pediatric critical care-associated AKI into distinct phenotypes is possible and may become an important prognostic tool.

Assessment of the renal angina index for the prediction of acute kidney injury in patients admitted to a European pediatric intensive care unit

BACKGROUND

Acute kidney injury (AKI) is associated with worse outcomes and increased morbidity and mortality in pediatric intensive care unit (PICU) patients. The renal angina index (RAI) has been proposed as an early prediction tool for AKI development.

OBJECTIVES

The objective was to evaluate outcomes of RAI-positive patients and to compare RAI performance with traditional AKI markers across different patient groups (medical/post-surgical). This was an observational retrospective study. All children admitted to a tertiary hospital PICU over a 3-year period were included. Electronic medical records were reviewed. Day 1 RAI was calculated, as was the presence and staging of day 3 AKI.

RESULTS

A total of 593 patients were included; 56% were male, the mean age was 55 months, and 17% had a positive RAI. This was associated with day 3 AKI development and worse outcomes, such as greater need for kidney replacement therapy, longer duration of mechanical ventilation, vasoactive support and PICU stay, and higher mortality. For all-stage kidney injury, RAI presented a sensitivity of 87.5% and a specificity of 88.1%. Prediction of day 3 all-stage AKI by RAI had an AUC=0.878; its performance increased for severe AKI (AUC = 0.93). RAI was superior to serum creatinine increase and KDIGO AKI staging on day 1 in predicting severe AKI development. The performance remained high irrespective of the type of admission.

CONCLUSIONS

The RAI is a simple and inexpensive tool that can be used with medical and post-surgical PICU patients to predict AKI development and anticipate complications, allowing for the adoption of preventive measures.

Clinical significance of frusemide stress test in predicting the severity of acute kidney injury

Introduction:

The outcomes of Acute Kidney Injury (AKI) remain dismal even today, owing in part due to the lack of an ideal biomarker for detecting renal damage early enough. We conducted this pilot study to determine the clinical significance of Frusemide Stress Test (FST) to predict the severity of AKI.

Methods:

A total of 80 patients with AKI-KDIGO (Kidney Disease: Improving Global Outcomes) stage 1 or stage 2 underwent FST by administering a bolus dose of frusemide (1mg/kg for frusemide naïve and 1.5mg/kg for prior frusemide exposure in the past week), and urine output was then measured for the next two hours with volume replacement as desirable. The progression to AKI-KDIGO stage 3 within 14 days of FST was studied as the primary outcome. The composite end point of achieving AKI-KDIGO stage 3 or death within 14 days of FST was studied as the secondary outcome.

Results:

Out of 80 patients, 28(35%) patients met the primary outcome, and 34(42.5%) patients met the secondary composite outcome. Except for baseline Chronic Kidney Disease (CKD) status (p=0.018), other demographic characteristics were comparable between progressors and non-progressors group. Using receiver operating characteristics (ROC) curve analysis, a cumulative 2-hour post-FST urine output of ≤300 mL predicted progression to stage 3 AKI with 82.14% sensitivity, 82.69% specificity, and AUC of 0.89±0.03 (p<0.0001).

Conclusion:

The FST showed promising results as a novel tubular biomarker to identify progression to severe AKI with good predictive ability.

The impact of biomarkers of acute kidney injury on individual patient care

Acute kidney injury (AKI) remains a common clinical syndrome associated with increased morbidity and mortality. In the last several years there have been several advances in the identification of patients at increased risk for AKI through the use of traditional and newer functional and damage biomarkers of AKI. This article will specifically focus on the impact of biomarkers of AKI on individual patient care, focusing predominantly on the markers with the most expansive breadth of study in patients and reported literature evidence. Several studies have demonstrated that close monitoring of widely available biomarkers such as serum creatinine and urine output is strongly associated with improved patient outcomes. An integrated approach to these biomarkers used in context with patient risk factors (identifiable using electronic health record monitoring) and with tests of renal reserve may guide implementation and targeting of care bundles to optimize patient care. Besides traditional functional markers, biochemical injury biomarkers have been increasingly utilized in clinical trials both as a measure of kidney injury as well as a trigger to initiate other treatment options (e.g. care bundles and novel therapies). As the novel measures are becoming globally available, the clinical implementation of hospital-based real-time biomarker measurements involves a multidisciplinary approach. This literature review discusses the data evidence supporting both the strengths and limitations in the clinical implementation of biomarkers based on the authors' collective clinical experiences and opinions.

Role of the Furosemide Stress Test in Renal Injury Prognosis

Risk stratification and accurate patient prognosis are pending issues in the management of patients with kidney disease. The furosemide stress test (FST) has been proposed as a low-cost, fast, safe, and easy-to-perform test to assess tubular integrity, especially when compared to novel plasma and urinary biomarkers. However, the findings regarding its clinical use published so far provide insufficient evidence to recommend the generalized application of the test in daily clinical routine. Dosage, timing, and clinical outcomes of the FST proposed thus far have been significantly different, which further accentuates the need for standardization in the application of the test in order to facilitate the comparison of results between series. This review will summarize published research regarding the usefulness of the FST in different settings, providing the reader some insights about the possible implications of FST in clinical decision-making in patients with kidney disease and the challenges that research will have to address in the near future before widely applying the FST.

Acute kidney injury overview: From basic findings to new prevention and therapy strategies

Acute kidney injury (AKI) is defined as a decrease in kidney function within hours, which encompasses both injury and impairment of renal function. AKI is not considered a pathological condition of single organ failure, but a syndrome in which the kidney plays an active role in the progression of multi-organ dysfunction. The incidence rate of AKI is increasing and becoming a common (8-16% of hospital admissions) and serious disease (four-fold increased hospital mortality) affecting public health costs worldwide. AKI also affects the young and previously healthy individuals affected by infectious diseases in Latin America. Because of the multifactorial pathophysiological mechanisms, there is no effective pharmacological therapy that prevents the evolution or reverses the injury once established; therefore, renal replacement therapy is the only current alternative available for renal patients. The awareness of an accurate and prompt recognition of AKI underlying the various clinical phenotypes is an urgent need for more effective therapeutic interventions to diminish mortality and socio-economic impacts of AKI. The use of biomarkers as an indicator of the initial stage of the disease is critical and the cornerstone to fulfill the gaps in the field. This review discusses emerging strategies from basic science toward the anticipation of features, treatment of AKI, and new treatments using pharmacological and stem cell therapies. We will also highlight bioartificial kidney studies, addressing the limitations of the development of this innovative technology.

Sepsis associated acute kidney injury

Sepsis is defined as organ dysfunction resulting from the host's deleterious response to infection. One of the most common organs affected is the kidneys, resulting in sepsis associated acute kidney injury (SA-AKI) that contributes to the morbidity and mortality of sepsis. A growing body of knowledge has illuminated the clinical risk factors, pathobiology, response to treatment, and elements of renal recovery that have advanced our ability to prevent, detect, and treat SA-AKI. Despite these advances, SA-AKI remains an important concern and clinical burden, and further study is needed to reduce the acute and chronic consequences. This review summarizes the relevant evidence, with a focus on the risk factors, early recognition and diagnosis, treatment, and long term consequences of SA-AKI. In addition to literature pertaining to SA-AKI specifically, pertinent sepsis and acute kidney injury literature relevant to SA-AKI was included.

Dynamic Biomarker Assessment: A Diagnostic Paradigm to Match the AKI Syndrome

Acute kidney injury (AKI) affects one in four neonates, children, and adults admitted to the intensive care unit (ICU). AKI-associated outcomes, including mortality, are significantly worsened. Several decades of research demonstrate evidence for a need to rethink the pathophysiology and drivers of injury as well as to reconsider the existing diagnostic framework. Novel urinary and serum biomarkers of injury have, however, not been readily integrated into practice-partially because of the limited scope to current testing. The predominant focus to date has been the adjudication of a single biomarker measured at a single point of time for the prediction of either AKI progression or disease-related mortality. This approach is pragmatically problematic. The imprecise, umbrella classification of AKI diagnosis coupled with the absence of a consistently effective set of therapies creates a difficult rubric for biomarkers to demonstrate value in the scope of practice. AKI is, however, not a binary process but more an ICU syndrome-with complex biology underpinning injury, interacting and disrupting other organ function, multidimensional in manifestation, and varying in severity over time. As such, a more appropriate diagnostic paradigm is needed. In this minireview, the status quo for AKI diagnosis and associated limitations will be discussed, and a novel, dynamic, and multidimensional paradigm will be presented. Appreciation of AKI as an ICU syndrome and creation of an appropriately matching and sophisticated diagnostic platform of injury assessment are possible and represent the next step in AKI management.

The Accuracy of Urinary TIMP-2 and IGFBP7 for the Diagnosis of Cardiac Surgery-Associated Acute Kidney Injury: A Systematic Review and Meta-Analysis

Background:

Tissue inhibitor of metalloproteinase 2 (TIMP-2) and insulin-like growth factor binding protein 7 (IGFBP7) are recent promising markers for identification of cardiac surgery-associated acute kidney injury (CSA-AKI). The aim of this study was systematically and quantitatively to evaluate the accuracy of urinary TIMP-2 and IGFBP7 for the diagnosis of CSA-AKI.

Methods:

Three databases including PubMed, ISI web of knowledge, and Embase were systematically searched from inception to March 2018. Two investigators conducted the processes of literature search study selection, data extraction, and quality evaluation independently. Meta-DiSc and STATA were used for all statistical analyses.

Results:

A total of 8 studies comprising 552 patients were included in this meta-analysis. Pooled sensitivity and specificity with corresponding 95% confidence intervals (CIs) were 0.79 (95% CI, 0.71-0.86, I 2 = 74.2%) and 0.76 (95% CI, 0.72-0.80, I 2 = 80.8%), respectively. Pooled positive likelihood ratio (LR), negative LR, and diagnostic odds ratio were 3.49 (95% CI, 2.44-5.00, I 2 = 61.5%), 0.31(95% CI, 0.19-0.51, I 2 = 51.8%), and 14.89 (95% CI, 7.31-30.32, I 2 = 27.9%), respectively. The area under curve estimated by summary receiver operating characteristic was 0.868 (standard error [SE] 0.032) with a Q* value of 0.799 (SE 0.032). Sensitivity analysis demonstrated that one study notably affected the stability of pooled results. One of the subgroups investigated—AKI threshold—could account for partial heterogeneity.

Conclusion:

Urinary TIMP-2 and IGFBP7 is a helpful biomarker for early diagnosis of CSA-AKI. And, the potential of this biomarker with a broader spectrum of clinical settings may be the focus of future studies.

Mechanisms Underlying Increased TIMP2 and IGFBP7 Urinary Excretion in Experimental AKI

BACKGROUND

Recent clinical data support the utility/superiority of a new AKI biomarker ("NephroCheck"), the arithmetic product of urinary TIMP × IGFBP7 concentrations. However, the pathophysiologic basis for its utility remains ill defined.

METHODS

To clarify this issue, CD-1 mice were subjected to either nephrotoxic (glycerol, maleate) or ischemic AKI. Urinary TIMP2/IGFBP7 concentrations were determined at 4 and 18 hours postinjury and compared with urinary albumin levels. Gene transcription was assessed by measuring renal cortical and/or medullary TIMP2/IGFBP7 mRNAs (4 and 18 hours after AKI induction). For comparison, the mRNAs of three renal "stress" biomarkers (NGAL, heme oxygenase 1, and p21) were assessed. Renal cortical TIMP2/IGFBP7 protein was gauged by ELISA. Proximal tubule-specific TIMP2/IGFBP7 was assessed by immunohistochemistry.

RESULTS

Each AKI model induced prompt (4 hours) and marked urinary TIMP2/IGFBP7 increases without an increase in renal cortical concentrations. Furthermore, TIMP2/IGFBP7 mRNAs remained at normal levels. Endotoxemia also failed to increase TIMP2/IGFBP7 mRNAs. In contrast, each AKI model provoked massive NGAL, HO-1, and p21 mRNA increases, confirming that a renal "stress response" had occurred. Urinary albumin rose up to 100-fold and strongly correlated (r=0.87-0.91) with urinary TIMP2/IGFBP7 concentrations. Immunohistochemistry showed progressive TIMP2/IGFBP7 losses from injured proximal tubule cells. Competitive inhibition of endocytic protein reabsorption in normal mice tripled urinary TIMP2/IGFBP7 levels, confirming this pathway's role in determining urinary excretion.

CONCLUSIONS

AKI-induced urinary TIMP2/IGFBP7 elevations are not due to stress-induced gene transcription. Rather, increased filtration, decreased tubule reabsorption, and proximal tubule cell TIMP2/IGFBP7 urinary leakage seem to be the most likely mechanisms.

The coming era of precision medicine for intensive care

Recent advances in technology and better understanding of mechanisms underlying disease are beginning to enable us to better characterize critically ill patients. Instead of using nonspecific syndromic groupings, such as sepsis or acute respiratory distress syndrome, we can now classify individual patients according to various specific characteristics, such as immune status. This "personalized" medicine approach will enable us to distinguish patients who have similar clinical presentations but different cellular and molecular responses that will influence their need for and responses (both negative and positive) to specific treatments. Treatments will be able to be chosen more accurately for each patient, resulting in more rapid institution of appropriate, effective therapy. We will also increasingly be able to conduct trials in groups of patients specifically selected as being most likely to respond to the intervention in question. This has already begun with, for example, some new interventions being tested only in patients with coagulopathy or immunosuppressive patterns. Ultimately, as we embrace this era of precision medicine, we may be able to offer precision therapies specifically designed to target the molecular set-up of an individual patient, as has begun to be done in cancer therapeutics.

The prognostic value of the furosemide stress test in predicting delayed graft function following deceased donor kidney transplantation

OBJECTIVES AND METHODS

The Furosemide Stress Test (FST) is a novel dynamic assessment of tubular function that has been shown in preliminary studies to predict patients who will progress to advanced stage acute kidney injury, including those who receive renal replacement therapy (RRT). The aim of this study is to investigate if the urinary response to a single intraoperative dose of intravenous furosemide predicts delayed graft function (DGF) in patients undergoing deceased donor kidney transplant.

RESULTS

On an adjusted multiple logistic regression, a single 100 mg dose of intraoperative furosemide after the anastomosis of the renal vessels (FST) predicted the need for RRT at 2 and 6 h post kidney transplantation (KT). Recipient urinary output was measured at 2 and 6 h post furosemide administration. In receiver-operating characteristic (ROC) analysis, the FST predicted DGF with an area-under-the curve of 0.85 at an optimal urinary output cut-off of <600 mls at 6 h with a sensitivity of and a specificity of 83% and 74%, respectively.

CONCLUSIONS

The FST is a predictor of DGF post kidney transplant and has the potential to identify patients requiring RRT early after KT.

Acute kidney injury-an overview of diagnostic methods and clinical management

Acute kidney injury (AKI) is a common condition in multiple clinical settings. Patients with AKI are at an increased risk of death, over both the short and long term, and of accelerated renal impairment. As the condition has become more recognized and definitions more unified, there has been a rapid increase in studies examining AKI across many different clinical settings. This review focuses on the classification, diagnostic methods and clinical management that are available, or promising, for patients with AKI. Furthermore, preventive measures with fluids, acetylcysteine, statins and remote ischemic preconditioning, as well as when dialysis should be initiated in AKI patients are discussed. The classification of AKI includes both changes in serum creatinine concentrations and urine output. Currently, no kidney injury biomarkers are included in the classification of AKI, but proposals have been made to include them as independent diagnostic markers. Treatment of AKI is aimed at addressing the underlying causes of AKI, and at limiting damage and preventing progression. The key principles are: to treat the underlying disease, to optimize fluid balance and optimize hemodynamics, to treat electrolyte disturbances, to discontinue or dose-adjust nephrotoxic drugs and to dose-adjust drugs with renal elimination.