Meghan E. Sise

Sensitivity and Specificity of a Single Emergency Department Measurement of Urinary Neutrophil Gelatinase–Associated Lipocalin for Diagnosing Acute Kidney Injury

Context Studies in surgical patients suggest that urinary neutrophil gelatinaseassociated lipocalin (NGAL) may be an effective test for diagnosing acute kidney injury. Contribution The authors measured markers of renal function in 635 consecutive adults who were admitted to the emergency department of 1 urban hospital; of these patients, 30 had a final clinical diagnosis of acute kidney injury. When urinary NGAL was at least 130 g/g creatinine, the test was highly discriminatory for acute kidney injury (sensitivity, 0.90; specificity, 0.995; positive likelihood ratio, 181.5; and negative likelihood ratio, 0.10). Caution Patients were from 1 setting in 1 hospital. Kidney diagnoses were clinical, not biopsy-proven. Implication Urinary NGAL is a promising test because of its large effect on the probability of acute kidney injury. The Editors Acute kidney injury is a common complication among ambulatory and hospitalized patients, and its incidence has increased by 11% in recent years (1). It is a rapidly progressive illness that independently predicts excess morbidity and mortality (24). Twenty percent to 60% of patients with acute kidney injury require dialysis (5), and mortality rates range from 15% in the community setting (2, 3) to 50% to 80% in the setting of multiorgan failure (6, 7) and more than 80% in the postoperative setting (8, 9). Less severe forms of acute kidney injury may also result in prolonged hospitalization (10). These characteristics contrast with those of other kidney diseases, such as chronic kidney disease, which is typified by an insidious decline in renal function and is usually nonprogressive during hospitalization. Acute kidney injury is also distinct from prerenal azotemia, a physiologic response of the kidney to various predisposing factors (volume depletion, diuretic use, reninangiotensin blockade) that promptly resolve on fluid administration, regimen modification, or amelioration of the extrakidney organ malfunction (11). It is critical to distinguish acute kidney injury from prerenal azotemia and chronic kidney disease at the time of patient presentation to rapidly manage associated illness. However, the initial measurement of serum creatinine, the standard marker of kidney function, does not distinguish acute kidney injury from prerenal azotemia (12) or chronic kidney disease. In addition, the initial measurement of serum creatinine cannot reflect the extent of injury because its accumulation always lags behind the insult (13). Even a large decline in glomerular filtration rate (GFR) may manifest as a small change in serum creatinine level, particularly in the initial 48 hours after acute kidney injury before steady-state equilibrium is reached (13, 14). Serum creatinine may also vary by age, race, sex, muscle mass, metabolism, nutritional status, comorbid conditions, hydration status, and medication use and consequently may not increase in proportion to the severity of the injury. As a result, the diagnosis of acute kidney injury currently requires measuring serum creatinine repeatedly and delaying maneuvers to prevent ongoing kidney damage, such as stopping use of nonsteroidal anti-inflammatory drugs, adjusting medication dosages, or correcting hemodynamic status. Even elevations of serum creatinine level that do not meet established criteria for acute kidney injury (15) are associated with excess mortality (16), prolonged hospitalization (17), functional decline (18), and greater financial costs (19), and this highlights the insensitivity of serum creatinine measurement as a diagnostic test. These limitations in the use of serum creatinine provide the rationale for the discovery of kidney proteins that are expressed at the onset of injury and are more sensitive and specific for the diagnosis of acute injury than current diagnostic tests. Neutrophil gelatinaseassociated lipocalin (NGAL) is secreted into the urine by the thick ascending limb of Henle and collecting ducts of the kidney (20, 21). At these sites, NGAL is likely to play a critical role in host defense by chelating ironsiderophore complexes that enhance microbial growth (2224) or mediate oxidative damage. In some segments of the nephron, NGAL may also recycle the iron complexes by endocytosis (25, 26). Urinary NGAL is expressed in proportion to the degree of acute injury (27), whereas in chronic kidney disease, urinary NGAL is expressed in patients with progressive but not stable kidney failure (22). Volume depletion or diuretics do not increase urinary NGAL levels in mice (28), again reflecting the specificity of NGAL for ongoing tubular damage. These observations suggest not only that urinary NGAL detects acute kidney injury but also that its degree of expression might distinguish among acute kidney injury, prerenal azotemia, and chronic kidney disease. In addition, because NGAL is detectable before the accumulation of serum creatinine (20, 27, 29), NGAL might be used to diagnose acute kidney injury at patient presentation even when changes in serum creatinine level are incipient. Because of the diagnostic ambiguities that occur with current tests at patient presentation, we conducted a prospective cohort study in an inner-city emergency department to determine the accuracy of urinary NGAL to identify acute kidney injury. We subsequently followed each participants hospital course to determine the relationship among the presenting level of NGAL and other urinary proteins, serum creatinine level, and patient outcome. Our hypothesis was that a single measurement of urinary NGAL is superior to conventional and novel biomarkers in predicting acute kidney injury and its comorbid conditions. Methods This study was approved by the Columbia University Medical Center Institutional Review Board, and informed consent was obtained before enrollment. We recruited consecutive patients 18 years and older who visited the Columbia University Medical Center emergency department between 6 a.m. and 12 a.m. from March to August 2007. We obtained the first sample of donated urine and blood. We excluded 17 patients who were receiving hemodialysis and 230 patients without subsequent creatinine measurements from further analysis (Figure 1). Figure 1. Study flow diagram. Diagnosis of Kidney Disease We defined altered kidney function by age- and sex-based criteria: men and women between 18 and 50 years of age with a serum creatinine level greater than 106 mol/L (>1.2 mg/dL), men older than 50 years with a level greater than 88.4 mol/L (>1.0 mg/dL), and women with a level greater than 70 mol/L (>0.8 mg/dL). We estimated GFR by using the Modification of Diet and Renal Disease formula (30). We determined baseline kidney function for 509 patients from a retrospective analysis of serum creatinine, medical history, and demographic characteristics recorded in the Columbia University Medical Center electronic records for the 1 to 12 months before admission. A prospective analysis of kidney function after hospital admission consisted of daily serum chemistry studies and renal ultrasonography. On the basis of the retrospective and prospective studies, a coordinator and an internist who were blinded to the experimental measurements independently assigned patients to 1 of 4 diagnostic categories (normal kidney function, nonprogressive chronic kidney disease, prerenal azotemia, or acute kidney injury); a nephrologist adjudicated the 24 cases of disagreement. We defined normal kidney function as a baseline estimated GFR greater than 60 mL/min per 1.73 m2 and no transient or sustained increases in serum creatinine level or decreases in estimated GFR during the patients stay in the hospital. We defined nonprogressive chronic kidney disease as a sustained and unchanging (<25% change from baseline) increase in serum creatinine level that met our criteria for altered kidney function and persisted for more than 3 months before hospitalization, reflecting a stably reduced estimated GFR of less than 60 mL/min per 1.73 m2 that is consistent with the National Kidney Foundations Kidney Disease Outcomes Quality Initiative definition of chronic kidney disease (31). In the absence of retrospective data, presumptive nonprogressive chronic kidney disease was diagnosed if patients had a sustained elevated serum creatinine level that did not change during hospitalization and reflected a stable estimated GFR of less than 60 mL/min per 1.73 m2 despite volume resuscitation. We defined prerenal azotemia as a new-onset increase in serum creatinine level that satisfied our criteria for altered kidney function and either resolved within 3 days with treatment aimed at restoring perfusion, such as intravenous volume repletion or discontinuation of diuretics (in the setting of historical and laboratory data suggesting decreased renal perfusion), or was accompanied by fractional excretion of sodium less than 1% at presentation. We defined acute kidney injury as a new-onset 1.5-fold increase in serum creatinine level or a 25% decrease in estimated GFR from baseline values that satisfied minimal RIFLE (risk for kidney dysfunction, injury to the kidney, failure of kidney function, loss of kidney function, and end-stage kidney disease) criteria for serum creatinine and GFR that was sustained for at least 3 days despite volume resuscitation. The RIFLE criteria provide a meaningful way to stratify patients at different stages of kidney failure on the basis of severity (risk, injury, failure) and outcome (loss and end-stage disease) (Appendix Table) (15). Appendix Table. The RIFLE Criteria We prospectively identified patient outcomes (nephrology consultation, intensive care admission, dialysis initiation, mortality) from electronic medical records. Laboratory Measurements We centrifuged the urine samples at 12000 rpm for 10 minutes and stored the supernatants at 80C. Urinary NGAL (10 L) was quantified by immunoblots with nonreducing 4% to 20% gradient polyacrylamide gels (Bio-Rad Labora

Diagnostic and Prognostic Stratification in the Emergency Department Using Urinary Biomarkers of Nephron Damage: A Multicenter Prospective Cohort Study

OBJECTIVES This study aimed to determine the diagnostic and prognostic value of urinary biomarkers of intrinsic acute kidney injury (AKI) when patients were triaged in the emergency department. BACKGROUND Intrinsic AKI is associated with nephron injury and results in poor clinical outcomes. Several urinary biomarkers have been proposed to detect and measure intrinsic AKI. METHODS In a multicenter prospective cohort study, 5 urinary biomarkers (urinary neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, urinary liver-type fatty acid binding protein, urinary interleukin-18, and cystatin C) were measured in 1,635 unselected emergency department patients at the time of hospital admission. We determined whether the biomarkers diagnosed intrinsic AKI and predicted adverse outcomes during hospitalization. RESULTS All biomarkers were elevated in intrinsic AKI, but urinary neutrophil gelatinase-associated lipocalin was most useful (81% specificity, 68% sensitivity at a 104-ng/ml cutoff) and predictive of the severity and duration of AKI. Intrinsic AKI was strongly associated with adverse in-hospital outcomes. Urinary neutrophil gelatinase-associated lipocalin and urinary kidney injury molecule 1 predicted a composite outcome of dialysis initiation or death during hospitalization, and both improved the net risk classification compared with conventional assessments. These biomarkers also identified a substantial subpopulation with low serum creatinine at hospital admission, but who were at risk of adverse events. CONCLUSIONS Urinary biomarkers of nephron damage enable prospective diagnostic and prognostic stratification in the emergency department.

Safety and efficacy of sofosbuvir-containing regimens in hepatitis C-infected patients with impaired renal function

Renal clearance is the major elimination pathway for sofosbuvir (SOF). We assessed the safety and efficacy of SOF‐containing regimens in patients with varying baseline estimated glomerular filtration rate (eGFR).

Treatment of hepatitis C virus–associated mixed cryoglobulinemia with direct-acting antiviral agents

Hepatitis C virus (HCV) is the most common cause of mixed cryoglobulinemia syndrome (MCS). The efficacy and safety of all‐oral direct‐acting antiviral (DAA) therapy in HCV‐associated MCS (HCV‐MCS) is largely unknown. The authors studied case series of patients with HCV‐MCS who were treated with sofosbuvir‐based regimens and historical controls treated with pegylated interferon and ribavirin in a single health care network. HCV‐MCS was defined by circulating cryoglobulin associated with systemic vasculitis symptoms. Renal involvement (n = 7) was established by kidney biopsy (n = 5) or by two or more of the following clinical findings: reduced kidney function, proteinuria, or hematuria with other causes excluded (n = 2). Twelve patients received DAA therapy between December 2013 and September 2014. Median age was 61 years, 58% were male, and 50% had cirrhosis. Median baseline serum creatinine was 0.97 mg/dL (range 0.7‐2.47). Four patients received rituximab concurrent with DAA therapy. Sustained virological response rate at 12 weeks (SVR12) was 83% overall. Patients with glomerulonephritis who achieved SVR12 experienced an improvement in serum creatinine and a reduction in proteinuria. Cryoglobulin levels decreased in 89% of patients, with median percent decreasing from 1.5% to 0.5% and completely disappearing in four of nine cases who had cryoglobulins measured after treatment. Serious adverse events were infrequent (17%). In contrast, the historical cohort treated with pegylated interferon and ribavirin experienced only 10% SVR12, with 100% experiencing at least one adverse event and 50% experiencing premature discontinuation due to adverse events. Conclusion: SVR12 rates for sofosbuvir‐based DAA regimens in HCV‐MCS were 83%, significantly higher than historical controls treated with pegylated interferon and ribavirin; patients with glomerulonephritis experienced improvement in renal function, including those not concomitantly treated with immunosuppression. (Hepatology 2016;63:408–417)

NGAL (Lcn2) monomer is associated with tubulointerstitial damage in chronic kidney disease

The rate of progression of chronic kidney disease (CKD) is difficult to predict using single measurements of serum creatinine or proteinuria. On the other hand, documented tubulointerstitial disease presages worsening CKD, but kidney biopsy is not practical for routine use and generally does not sample the tubulointerstitial compartment of the medulla. Perhaps a urine test that correlates with specific histological findings may serve as a surrogate for the kidney biopsy. Here we compared both immunoblot analysis (under non-reducing conditions) and a commercially available monomer immunoassays of Neutrophil Gelatinase Associated Lipocalin (NGAL) with pathological changes found in kidney biopsies, to determine whether specific histological characteristics associated with a specific NGAL species. We found that the urine of patients with advanced CKD contained NGAL monomers as well as higher molecular weight complexes containing NGAL, identified by MALDI-TOF/TOF mass spectroscopy. The NGAL monomer significantly correlated with glomerular filtration rate, interstitial fibrosis and tubular atrophy. Hence, specific assays of the NGAL monomer implicate histology associated with progressive, severe CKD.The type and the extent of tissue damage inform the prognosis of chronic kidney disease (CKD), but kidney biopsy is not a routine test. Urinary tests that correlate with specific histological findings might serve as surrogates for the kidney biopsy. We used immunoblots and ARCHITECT-NGAL assays to define the immunoreactivity of urinary neutrophil gelatinase-associated lipocalin (NGAL) in CKD, and we used mass spectroscopy to identify associated proteins. We analyzed kidney biopsies to determine whether specific pathological characteristics associated with the monomeric NGAL species. Advanced CKD urine contained the NGAL monomer as well as novel complexes of NGAL. When these species were separated, we found a significant correlation between the NGAL monomer and glomerular filtration rate (r=-0.53, P<0.001), interstitial fibrosis (mild vs. severe disease; mean 54 vs. 167 μg uNGAL/g Cr, P<0.01), and tubular atrophy (mild vs. severe disease; mean 54 vs. 164 μg uNGAL/g Cr, P<0.01). Monospecific assays of the NGAL monomer demonstrated a correlation with histology that typifies progressive, severe CKD.

Reference values of urinary neutrophil gelatinase-associated lipocalin in very low birth weight infants.

In very low birth weight (VLBW) infants, acute renal impairment (ARI) is common, but there is no consensus about criteria for its diagnosis. Neutrophil gelatinase-associated lipocalin (NGAL) is an early and sensitive indicator of renal impairment in experimental animals, children, and adults. Urinary NGAL (UNGAL) is detectable in VLBW infants; however, there is no reference range in this population. The objective of this study is to define the reference range for UNGAL in VLBW infants with no risk factors for acute renal impairment. UNGAL concentration was determined in urine samples collected from day of life (DOL) 4 through DOL 30 in 50 newborns with uncomplicated clinical courses, selected from a total of 145 prospectively enrolled appropriate for gestational age inborn VLBW premature infants. The birth weight and gestational age ranges were 790-1490 g and 26–33 wk, respectively. The median, 95th and 99th percentiles, and range of pooled UNGAL values were 5 ng/mL, 50 ng/mL, 120 ng/mL, and 2–150 ng/mL, respectively. Greater variability and higher quantile levels of UNGAL were observed in females versus males. In conclusion, a reference range for UNGAL in VLBW infants, similar to that in children and adults, has been established.

Urinary NGAL Marks Cystic Disease in HIV-Associated Nephropathy

Nephrosis and a rapid decline in kidney function characterize HIV-associated nephropathy (HIVAN). Histologically, HIVAN is a collapsing focal segmental glomerulosclerosis with prominent tubular damage. We explored the expression of neutrophil gelatinase-associated lipocalin (NGAL), a marker of tubular injury, to determine whether this protein has the potential to aid in the noninvasive diagnosis of HIVAN. We found that expression of urinary NGAL was much higher in patients with biopsy-proven HIVAN than in HIV-positive and HIV-negative patients with other forms of chronic kidney disease. In the HIV-transgenic mouse model of HIVAN, NGAL mRNA was abundant in dilated, microcystic segments of the nephron. In contrast, urinary NGAL did not correlate with proteinuria in human or in mouse models. These data show that marked upregulation of NGAL accompanies HIVAN and support further study of uNGAL levels in large cohorts to aid in the noninvasive diagnosis of HIVAN and screen for HIVAN-related tubular damage.

Efficacy and Safety of Direct Acting Antivirals in Kidney Transplant Recipients with Chronic Hepatitis C Virus Infection

The prevalence of Hepatitis C Virus (HCV) infection is significantly higher in patients with end-stage renal disease compared to the general population and poses important clinical challenges in patients who undergo kidney transplantation. Historically, interferon-based treatment options have been limited by low rates of efficacy and significant side effects, including risk of precipitating rejection. Limited data exist on the use of all-oral, interferon-free direct-acting antiviral (DAA) therapies in kidney transplant recipients. In this study, we performed a retrospective chart review with prospective clinical follow-up of post-kidney transplant patients treated with DAA therapies at three major hospitals in Boston, MA. A total of 24 kidney recipients with HCV infection received all-oral DAA therapy post-transplant. Patients were predominantly male (79%) with a median age of 60 years (range 34–70 years), median creatinine of 1.2 mg/dL (0.66–1.76), and 42% had advanced fibrosis or cirrhosis. The majority had HCV genotype 1a infection (58%). All patients received full-dose sofosbuvir; it was paired with simeprevir (9 patients without and 3 patients with ribavirin), ledipasvir (7 patients without and 1 patient with ribavirin) or ribavirin alone (4 patients). The overall sustained virologic response (SVR12) was 91% (21 out of 23 patients). One patient achieved SVR4 but demised prior to SVR12 check point due to treatment unrelated cause. Two treatment failures were successfully retreated with alternative DAA regimens and achieved SVR. Both initials failures occurred in patients with advanced fibrosis or cirrhosis, with genotype 1a infection, and prior HCV treatment failure. Adverse events were reported in 11 patients (46%) and were managed clinically without discontinuation of therapy. Calcineurin inhibitor trough levels did not significantly change during therapy. In this multi-center series of patients, all-oral DAA therapy appears to be safe and effective in post-kidney transplant patients with chronic HCV infection.

Intralesional Sodium Thiosulfate for the Treatment of Calciphylaxis

IMPORTANCE Calciphylaxis is a potentially fatal disorder of abnormal calcium deposition. Patients commonly present with painful retiform to stellate purpuric lesions that often undergo ulceration and necrosis, increasing the risk of infection and life-threatening sepsis. Treatment is multifaceted, and improved outcomes have been demonstrated with intravenous sodium thiosulfate; however, the use of this medication can be limited by its adverse effects. The use of topical sodium thiosulfate has been successfully reported for superficial calcium deposits in the skin from other processes. Therefore, we hypothesized that intralesional (IL) sodium thiosulfate may be an effective treatment for the deeper lesions of cutaneous calciphylaxis. We provide a retrospective case review of 4 patients with calciphylaxis who were treated with IL sodium thiosulfate. OBSERVATIONS Four patients with biopsy-proven cutaneous calciphylaxis were treated with IL sodium thiosulfate (250 mg/mL) in areas of clinically active disease. The patients tolerated the medication well, with only transient localized discomfort during injection. All 4 patients had complete healing of their ulcers and remission of disease. CONCLUSIONS AND RELEVANCE Intralesional sodium thiosulfate may be an effective and well-tolerated treatment for localized calciphylaxis. This novel approach requires further research and investigation.

Urinary Neutrophil Gelatinase-Associated Lipocalin Is a Promising Biomarker for Late Onset Culture-Positive Sepsis in Very Low Birth Weight Infants

Need for the early identification of sepsis in very low birth weight (VLBW) infants has led to the search for reliable biomarkers. This study aims to determine whether urinary neutrophil gelatinase-associated lipocalin (uNGAL) rises in culture-positive sepsis and, if so, is elevated at the time sepsis is suspected. This is a prospective study of 91 VLBW infants whose urine was collected daily for uNGAL analysis. In 65 episodes of suspected sepsis, four groups were identified: a) culture-positive sepsis; b) single culture positive for Staphylococcus epidermidis; c) and d) negative culture with antibiotic treatment for ≥7 d and <7 d, respectively. Daily means of uNGAL of each group were estimated for comparison. Mean uNGAL in group A (179 ng/mL) was significantly elevated on the day blood culture was drawn (day 0) compared with the mean of healthy VLBW infants (6.5 ng/mL), and to the means in groups B, C, and D (p < 0.05). In group A, mean uNGAL was significantly elevated on day 0 and daily for 5 days when compared with that of the day before culture (p < 0.05 to <0.005). uNGAL shows promise as an early marker for culture-positive sepsis in VLBW infants.