Fractional Excretion of Sodium and Urea in Differentiating Acute Kidney Injury Phenotypes in Decompensated Cirrhosis

Renal Dysfunction and Liver Transplantation

Renal dysfunction is common in patients undergoing liver transplant (LT) evaluation, thereby making it imperative for hepatologists to know how to diagnose, manage, and optimize treatment of acute kidney injury (AKI) and chronic kidney disease. This article reviews pre-transplant, peri-transplant, and post-transplant AKI diagnosis and management, and the role of renal replacement therapy in LT candidates.

An early warning model for predicting major adverse kidney events within 30 days in acute pancreatitis patients

BACKGROUND

Renal impairment is a common outcome of acute pancreatitis. Nevertheless, research on predictive models for major adverse kidney events within 30 days (MAKE30) in acute pancreatitis (AP) has been scarce.

METHODS

A retrospective study was conducted at Gansu Provincial Hospital, involving 391 patients with acute pancreatitis who were categorized into non-MAKE30 (320 cases) and MAKE30 (71 cases) groups. Univariate and multivariate logistic regression analyses were performed to determine the independent risk factors for MAKE30 in the aforementioned patient cohort. The nomogram was developed utilizing findings from a multivariate logistic regression analysis. Subsequent evaluation of the nomogram involved the use of receiver operating characteristic (ROC) curves, calibration curves, and decision curve analysis. Additionally, subgroup analyses were performed to different AP etiology and assess secondary outcomes.

RESULTS

Gender, respiratory rate (RR), creatinine (Cr), interleukin 6 (IL-6), prothrombin time (PT), and cardiovascular disease (CVD) were identified as associated predictors of Major Adverse Kidney Events within 30 days (MAKE30) in patients with acute pancreatitis. A nomogram model was developed based on these predictors. Evaluation using receiver operating characteristic (ROC) curve, calibration curve, and decision curve analyses (DCA) demonstrated that the nomogram model exhibited significant discrimination (AUC = 0.842) > the SOFA score (AUC = 0.809), excellent calibration, and substantial clinical utility. Subgroup analysis showed the nomogram model provided good predictive value for both secondary outcomes and various etiologies.

CONCLUSION

This model shows promise in efficiently and accurately evaluating the risk of developing MAKE30 in acute pancreatitis patients within the first 24 h of hospitalization.

Utility of fractional excretion of urea in acute kidney injury with comparison to fractional excretion of sodium: A systematic review and meta-analysis

BACKGROUND

Differentiating between intrinsic and prerenal acute kidney injury (AKI) presents a challenge. Here, we assessed the performance of the fractional excretion of urea (FEUrea) and compared it to the fractional excretion of sodium (FENa) in distinguishing intrinsic from prerenal AKI.

METHODS

A thorough search was conducted in several databases until January 16, 2024. We included studies evaluating FEUrea, with or without FENa, for differentiating AKI etiologies in adults. We assessed the methodological quality using the QUADAS-2 and QUADAS-C tools. We performed a meta-analysis using the bivariate random effects model, with subgroup analyses to explore the impact of diuretic therapy on FEUrea, and direct statistical comparisons between FEUrea and FENa involving the subgroups with and without diuretics.

RESULTS

We included 11 studies with 1108 hospitalized patients. Among eight studies (915 patients) evaluating FEUrea >35% for distinguishing intrinsic from prerenal AKI, the pooled sensitivity and specificity were 66% (95% CI, 49%-79%) and 75% (95% CI, 60%-85%), respectively. In a subset of six studies (302 patients) comparing FEUrea at 35% to FENa at 1% in patients not receiving diuretics, there were no significant differences in sensitivity (77% versus 89%, P = 0.410) or specificity (80% versus 79%, P = 0.956). In four studies, 244 patients on diuretics, FEUrea demonstrated lower sensitivity (52% versus 92%, P < 0.001) but higher specificity (82% versus 44%, P < 0.001) compared to FENa for the diagnosis of intrinsic AKI.

CONCLUSIONS

FEUrea has limited utility in differentiating intrinsic from prerenal AKI. FEUrea does not provide a superior alternative to FENa, even in patients receiving diuretics.

Hepatorenal Syndrome Type 1: Diagnosis and Treatment

Hepatorenal syndrome (HRS) is a feared complication in patients with advanced cirrhosis and is associated with significant morbidity and mortality. While recognized as a distinct physiologic condition for well over one hundred years, a lack of objective diagnostic tests has made the diagnosis one of exclusion. Since 1979, multiple sets of diagnostic criteria have been proposed. Though varying in detail, the principal intent of these criteria is to identify patients with severe, functional acute kidney injury that is unresponsive to volume resuscitation and exclude those with structural injury. However, accurate differential diagnosis remains challenging. Recently, multiple urinary biomarkers of kidney injury, including neutrophil gelatinase-associated lipocalin, have been studied as a means of objectively phenotyping etiologies of acute kidney injury in patients with cirrhosis. Along with markers reflecting tubular functional integrity, including the fractional excretion of sodium, injury markers will likely be incorporated into future diagnostic criteria. Making an accurate diagnosis is critical, as therapeutic options exist for HRS but must be given in a timely manner and only to those patients likely to benefit. Terlipressin, an analog of vasopressin, is the first line of therapy for HRS in much of the world and has recently been approved for use in the United States. Significant questions remain regarding the optimal dosing strategy, metrics for titration, and the potential role of point-of-care ultrasound to help guide concurrent albumin administration.

New biomarkers in acute kidney injury

Acute kidney injury (AKI) is a commonly encountered clinical syndrome. Although it often complicates community acquired illness, it is more common in hospitalized patients, particularly those who are critically ill or who have undergone major surgery. Approximately 20% of hospitalized adult patients develop an AKI during their hospital care, and this rises to nearly 60% in the critically ill, depending on the population being considered. In general, AKI is more common in older adults, in those with preexisting chronic kidney disease and in those with known risk factors for AKI (including diabetes and hypertension). The development of AKI is associated with an increase in both mortality and morbidity, including the development of post-AKI chronic kidney disease. Currently, AKI is defined by a rise in serum creatinine from either a known or derived baseline value and/or oliguria or anuria. However, clinicians may fail to recognize the initial development of AKI because of a delay in the rise of serum creatinine or because of inaccurate urine output monitoring. This, in turn, delays any putative measures to treat AKI or to limit its degree. Consequently, efforts have focused on new biomarkers associated with AKI that may allow early recognition of this syndrome with the intent that this will translate into improved patient outcomes. Here we outline current biomarkers associated with AKI and explore their potential in aiding diagnosis, understanding the pathophysiology and directing therapy.

Hepatorenal Syndrome-Novel Insights into Diagnostics and Treatment

Hepatorenal syndrome (HRS) is a disorder associated with cirrhosis and renal impairment, with portal hypertension as its major underlying cause. Moreover, HRS is the third most common cause of acute kidney injury, thus creating a major public health concern. This review summarizes the available information on the pathophysiological implications of HRS. We discuss pathogenesis associated with HRS. Mechanisms such as dysfunction of the circulatory system, bacterial infection, inflammation, impaired renal autoregulation, circulatory, and others, which have been identified as critical pathways for development of HRS, have become easier to diagnose in recent years. Additionally, relatively recently, renal dysfunction biomarkers have been found indicating renal injury, which are involved in the pathophysiology of HRS. This review also summarizes the available information on the management of HRS, focusing on vasoconstrictive drugs, renal replacement therapy, and liver transplant together with currently being investigated novel therapies. Analyzing new discoveries for the underlying causes of this condition assists the general research to improve understanding of the mechanism of pathophysiology and thus prevention of HRS.

Predictors of Short-term Mortality in Patients of Cirrhosis of Liver Presenting as Acute Kidney Injury: An In-hospital Prospective Observational Study

Background

Acute kidney injury (AKI) is known to be associated with increased short-term mortality among cirrhotic patients. On this background, we designed this study to evaluate various causes of AKI among admitted patients with cirrhosis of liver and predictors of 90-day mortality.

Methods

One hundred and two consecutive adult patients with cirrhosis of liver with AKI hospitalized between November 2016 and March 2018 were enrolled in this prospective study. Their detailed clinical profile, including biochemical parameters, the etiology of AKI, and their clinical outcome of survival or mortality at 90-days, were recorded.

Results

The most common causes of AKI were infections, followed by hypovolemia, seen in 55.88% and 31.37% of the patients, respectively. Hepatorenal syndrome (HRS) was seen in 10.78%, while parenchymal renal disease was the least common (1.9%). The in-hospital mortality rate was 28.4%, while 90-day mortality was 39.21%. The HRS group had a high 90-day mortality rate of 54.54%. ROC analysis of various biochemical parameters revealed that serum creatinine (sCr), Model for End-Stage Liver Disease (MELD), International Normalized Ratio (INR), and Neutrophil-Lymphocyte ratio (NLR), followed by Child Turcotte Pugh (CTP), had high area under the curves of 0.785, 0.773, 0.747, 0.740, and 0.718, respectively, for the prediction of 90-day mortality.

Conclusion

Infection is the commonest cause of AKI in cirrhosis; however, mortality in patients with HRS-AKI is higher than that in those with infection-related AKI. Serum creatinine at admission, INR, NLR, and CTP scores predict short-term mortality among patients with AKI in cirrhosis. Further, large prospective studies are needed to confirm these findings.

Diagnostic value of combined detection of urine NGAL, KIM-1, and TFF3 in acute tubular necrosis associated with cirrhosis

BACKGROUND

Acute kidney injury (AKI) is a common complication of decompensated cirrhosis with high clinical mortality and poor prognosis, of which acute tubular necrosis (ATN) has the worst prognosis. Timely and accurate identification of ATN is a difficult problem to solve clinically. Previous studies have shown that urinary neutrophil gelatinase-associated lipocalin (NGAL), trefoil factor 3 (TFF3), and kidney injury molecule-1 (KIM-1) have potential value in the differential diagnosis of ATN and other types of AKI in patients with liver cirrhosis, but they still cannot be applied in clinical practice due to the low diagnostic efficacy. It is necessary to further explore whether the combined detection of the indicators can improve their diagnostic efficacy for ATN associated with cirrhosis.

AIM

To analyze the value of urinary NGAL, KIM-1, and TFF3, either alone or in combination, in the differential diagnosis of ATN in patients with cirrhosis complicated with AKI, and explore the cut-off values of urinary NGAL and other indicators in the differential diagnosis of ATN.

METHODS

A total of 190 patients with decompensated cirrhosis were selected, including 108 patients with AKI. They were divided into different subgroups according to the cause of AKI, including 33 cases of prerenal azotemia, 27 cases of acute renal injury with hepatorenal syndrome, and 48 cases of ATN. The value of urinary NGAL, TFF3, and KIM-1, either alone or in combination, in the differential diagnosis of ATN in patients with cirrhosis complicated with AKI was then assessed.

RESULTS

Urinary NGAL was of great value in the differential diagnosis of ATN in patients with cirrhosis complicated with AKI. The area under the curve (AUC) was 0.902; when the diagnostic threshold was 271.8 μg/g Cr, the sensitivity was 81.3% and the specificity was 85.0%. The combination of two biomarkers could improve the efficacy of differential diagnosis, with the diagnostic perfomance of urinary NGAL combined with urinary TFF3 being the best (AUC = 0.933, sensitivity 85.4%, specificity 88.3%).

CONCLUSION

Urinary NGAL, KIM-1, and TFF3 are of great value in differentiating ATN from other types of AKI in patients with cirrhosis. The combined detection of any two of these biomarkers can further improve the diagnostic efficiency, which is worthy of further study and clinical promotion.

The Diagnosis and Non-pharmacological Management of Acute Kidney Injury in Patients with Cirrhosis

Acute kidney injury in patients with cirrhosis is quite common, and is seen in up to 50% of patients hospitalized for decompensated cirrhosis. Causes of acute kidney injury include prerenal, renal, or postrenal etiologies. The diagnosis and early institution of nonpharmacologic and pharmacologic management are key to the recovery of renal function. The objective of this review is to provide a practical approach to the use of diagnostic biomarkers and highlight the nonpharmacologic management and prevention of acute kidney injury.

Advances in the diagnosis and management of hepatorenal syndrome: insights into HRS-AKI and liver transplantation

In hepatorenal syndrome-acute kidney injury (HRS-AKI), accurate and early diagnosis is crucial. HRS is a severe condition seen in advanced cirrhosis, requiring prompt recognition and proper management to enhance patient outcomes. Diagnosis of HRS-AKI relies on serum creatinine elevations, similar to other AKI cases in cirrhosis. However, distinguishing HRS-AKI from other renal impairments in these patients can be challenging. Biomarkers and clinical criteria aid in diagnosis and guide treatment. The management of HRS-AKI initially involves improving the haemodynamic profile using albumin and vasoconstrictors like terlipressin, a synthetic vasopressin analogue. Despite some reports linking terlipressin to increased adverse events compared with norepinephrine, it remains the preferred choice in HRS-AKI and acute-on-chronic liver failure due to its faster, stronger response and improved survival. Additional therapies like midodrine (alpha-1 adrenergic agonist), octreotide (somatostatin analogue) and transjugular intrahepatic portosystemic shunt are proposed as adjuvant treatments for HRS-AKI, aiming to improve vasoconstriction and renal blood flow. However, these adjunctive therapies cannot replace the definitive treatment for HRS-AKI-liver transplantation (LT). In cases unresponsive to medical management, LT is the only option to restore liver function and improve renal outcomes. Current evidence favours combined liver and kidney transplantation (CLKT) in certain situations. This review aims to evaluate the present evidence and recommendations on AKI in patients with cirrhosis, the pathophysiology of HRS-AKI, different treatments and indications for LT and CLKT. Understanding the complexities of managing HRS-AKI is crucial for optimising patient care and achieving better outcomes in this challenging clinical setting.

Role of urine/serum NGAL ratio in differential diagnosis of acute kidney injury in patients with cirrhosis

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL) can be used for the differential diagnosis of acute kidney necrosis (ATN) and other types of acute kidney injury (AKI) in patients with liver cirrhosis complicated with AKI. However, serum NGAL is directly related to urine NGAL, and there are few existing studies on the role of urine /serum NGAL ratio in the differential diagnosis of ATN.

AIM

To assess the significance of serum and urine NGAL as well as urine/serum NGAL ratio in differentiating ATN from other types of AKI in cirrhosis.

METHODS

A total of 180 patients with decompensated cirrhosis were included in the study, of whom 98 were complicated with AKI. According to the etiology of AKI, there were 33 patients with prerenal azotemia, 25 with hepatorenal syndrome-AKI, and 40 with ATN. The patients were divided into different subgroups to assess the value of NGAL in differentiating the types of AKI.

RESULTS

Urine NGAL and urine/serum NGAL ratio showed signi-ficant value in the differential diagnosis of ATN in patients with liver cirrhosis. At an optimal cut-off of 271.35 ng/mL, urine NGAL distinguished ATN from other types of AKI (area under the cuve [AUC] = 0.964; sensitivity, 87.5%; specificity, 96.6%). As well, at an optimal cut-off of 2.96, urine/serum NGAL ratio could also distinguish ATN from other types of AKI (AUC = 0.953, sensitivity 92.5% and specificity 91.4%).

CONCLUSION

Urine NGAL and urine/serum NGAL ratio have significant value in the differential diagnosis of ATN and other types of AKI in patients with liver cirrhosis, which is worthy of further study and clinical promotion.

Hepatorenal Syndrome: Pathophysiology, Diagnosis, and Treatment

Hepatorenal syndrome (HRS) is a primarily functional form of acute kidney injury (AKI) that develops in patients with decompensated cirrhosis. The pathophysiologic cascade that leads to HRS begins with pooling of blood in the splanchnic system, resulting in a decrease in effective circulating arterial volume. The definitive treatment of HRS is liver transplantation. When this is not possible, HRS is treated with a combination of vasoconstrictor agents and intravenous albumin. Although the combination of midodrine and octreotide is used in the United States, the recently approved terlipressin, an analog of vasopressin, is likely to become the first-line standard of care.

Novel biomarkers of acute kidney injury in chronic liver disease: Where do we stand after a decade of research?

Acute kidney injury (AKI) is a frequently encountered complication in decompensated chronic liver disease (CLD) with an estimated prevalence of 20%-50% among hospitalized patients. AKI often heralds the onset of a downhill course in the natural history of CLD. Serum creatinine has several limitations as a stand-alone marker of AKI in patients with decompensated CLD. The concept of hepatorenal syndrome, the prototype of AKI in decompensated CLD, has evolved tremendously over recent years. There is emerging evidence of an additional "structural" component in the pathophysiology of hepatorenal syndrome-AKI, which was previously identified as a purely "functional" form of renal impairment. Lacunae in the existent biochemical arsenal for diagnosis and prognosis of AKI have fueled enthusiastic research in the field of novel biomarkers of kidney injury in patients with cirrhosis. The advent of these biomarkers provides a crucial window of opportunity to improve the diagnosis and clinical outcomes of this vulnerable cohort of patients. This review summarizes the dynamic concept of renal dysfunction in CLD and the available literature on the role of novel biomarkers of AKI in assessing renal function, identifying AKI subtypes, and predicting prognosis. There is special emphasis on the renal tubular injury marker, neutrophil gelatinase-associated lipocalin, the most exhaustively studied biomarker of AKI in the CLD population.

Diagnostic Performance of Fractional Excretion of Sodium for the Differential Diagnosis of Acute Kidney Injury: A Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVES

AKI is classified as prerenal, intrinsic, and postrenal. Prerenal AKI and intrinsic AKI represent the most common causes for AKI in hospitalized patients. This study aimed to examine the accuracy of the fractional excretion of sodium for distinguishing intrinsic from prerenal AKI.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We searched MEDLINE, Embase, Cochrane Central Register of Controlled Trials, the Cochrane Library, and Scopus for all available studies that met the criteria until December 31, 2021. We included studies that evaluated fractional excretion of sodium in differentiating AKI etiologies in adults, whereas studies that did not have sufficient data to extract a 2×2 table were excluded. We assessed the methodologic quality using the Quality Assessment of Diagnostic Accuracy Studies-2 tool and extracted the diagnostic accuracy data for all included studies. We conducted a meta-analysis using the bivariate random effects model. We performed subgroup analysis to investigate sources of heterogeneity and the effect of the relevant confounders on fractional excretion of sodium accuracy.

RESULTS

We included 19 studies with 1287 patients. In a subset of 15 studies (872 patients) that used a threshold of 1%, the pooled sensitivity and specificity for differentiating intrinsic from prerenal AKI were 90% (95% confidence interval, 81% to 95%) and 82% (95% confidence interval, 70% to 90%), respectively. In a subgroup of six studies (511 patients) that included CKD or patients on diuretics, the pooled sensitivity and specificity were 83% (95% confidence interval, 64% to 93%) and 66% (95% confidence interval, 51% to 78%), respectively. In five studies with 238 patients on diuretics, the pooled sensitivity and specificity were 80% (95% confidence interval, 69% to 87%) and 54% (95% confidence interval, 31% to 75%), respectively. In eight studies with 264 oliguric patients with no history of CKD or diuretic therapy, the pooled sensitivity and specificity were 95% (95% confidence interval, 82% to 99%) and 91% (95% confidence interval, 83% to 95%), respectively.

CONCLUSIONS

Fractional excretion of sodium has a limited role for AKI differentiation in patients with a history of CKD or those on diuretic therapy. It is most valuable when oliguria is present.