Evaluation of the optimal neutrophil gelatinase-associated lipocalin value as a screening biomarker for urinary tract infections in children

Evaluation of diagnostic accuracy of urine neutrophil gelatinase-associated lipocalin in patients with symptoms of urinary tract infections: a meta-analysis

Introduction

Early and accurate diagnosis of urinary tract infection (UTI) can prevent serious sequelae including chronic kidney disease. Multiple individual studies have identified urine neutrophil gelatinase-associated lipocalin (uNGAL) as a promising biomarker for early diagnosis of UTI. We sought to understand the distribution and diagnostic accuracy of uNGAL values in patients presenting with UTI symptoms.

Methods

Our systematic literature reviews in PubMed, Embase, and Cochrane Reviews up to March 2024, identified 25 studies reporting mean/median, standard deviation/quartiles, and detection limits of uNGAL in symptomatic patients with and without culture-confirmed UTI. Seventeen studies were in children. Meta-analyses were performed using the quantile estimation (QE) method estimating the distributions of uNGAL, which were then compared between the UTI and non-UTI groups for identifying the best cut-off points maximizing the Youden index. Sensitivity analyses were performed on all 25 studies including adult patients.

Results

We found that uNGAL levels were significantly higher in samples with confirmed UTI compared to those without. In pediatric studies, median and 95% confidence interval (CI) of uNGAL values were 22.41 (95% CI of 9.94, 50.54) ng/mL in non-UTI group vs. 118.85 (95% CI of 43.07, 327.97) ng/mL in UTI group. We estimated the cut-off point of 48.43 ng/mL with highest sensitivity (96%) and specificity (97%) in children. Sensitivity analysis including both pediatric and adult studies yielded similar results.

Discussion

The level of uNGAL in symptomatic patients with confirmed UTI is much higher than that reported in patients without UTI. It may be used as a diagnostic tool to identify UTI early among symptomatic patients. The range of uNGAL concentrations and cut-off points reported in subjects with UTI is much lower than that reported in patients with acute intrinsic kidney injury.

Systematic Review Registration

https://www.crd.york.ac.uk/, PROSPERO (CRD42023370451).

Diagnostic Value of Urine Ribonuclease 7 (RNase 7) to Creatinine Ratio for Detecting Urinary Tract Infection in Children with Pyuria

Objective Ribonuclease 7 (RNase 7) is one of the members of the antimicrobial peptides playing a role in maintaining urinary tract sterility. We aimed to investigate the predictive value of the urine RNase 7 levels in children with pyuria and associations between RNase 7 and vesicoureteral reflux (VUR) and renal scarring.

Methods This study included 109 children with pyuria (46 febrile urinary tract infections [UTIs], 38 nonfebrile UTIs, and 25 sterile pyuria) whose RNase 7 levels were measured by enzyme-linked immunoassay. The results for urine RNase 7 concentrations were expressed as micrograms per milligrams creatinine.

Results RNase 7/Cr levels were higher in patients with both febrile and nonfebrile UTIs than the patients with sterile pyuria (p = 0.001). RNase 7/Cr had predictive values of diagnosis of febrile and nonfebrile UTIs (cut-off value: 2.92 µg/mg, p = 0.003; cut-off value: 3.67 µg/mg, p < 0.001, respectively). RNase 7/Cr had higher levels in the patients with VUR than without VUR (cut-off value: 4.28 µg/mg, p = 0.037). The patients with renal scarring had higher urine RNase 7/Cr than those without scarring (cut-off value: 4.54 µg/mg, p = 0.041).

Conclusion The evaluation of RNase 7/Cr may help prevent unnecessary and/or inappropriate antibiotic use in children with pyuria. The higher RNase 7 levels in patients with VUR and renal scarring may reflect long-term inflammation or greater inflammatory response during acute infection.

The Utility of Neutrophil Gelatinase-Associated Lipocalin in the Detection of Emerging Lung Injury due to Mechanical Ventilation in Children: A Preliminary Study

OBJECTIVE

Lung injuries are mostly ignored in patients supported by mechanical ventilation. Neutrophil gelatinase-associated lipocalin has come into prominence as an early sensitive and highly predictive biomarker of inflammation. The purpose of the study was to assess the capability of neutrophil gelatinase-associated lipocalin in recognizing lung injuries in children requiring mechanical ventilation.

MATERIALS AND METHODS

This prospective case-controlled study was carried out in a tertiary pediatric intensive care unit. The entire study group consisted of a total of 45 patients, 15 in the patient group (supported by invasive mechanical ventilation) and 30 in the control group (self-breathing). Whether lung injuries developed or not was investigated by measuring serumneutrophil gelatinase-associated lipocalin and urine-neutrophil gelatinase-associated lipocalin levels in the course of ventilation support.

RESULTS

In the patient group supported by mechanical ventilation, mean levels of serum-neutrophil gelatinase-associated lipocalin and urine-neutrophil gelatinase-associated lipocalin were measured as 192 ± 136.7 ng/mL and 43.7 ± 57.5 ng/mL, respectively. In the control group (self-breathing patients), mean levels of serum-neutrophil gelatinase-associated lipocalin and urine-neutrophil gelatinase-associated lipocalin were found as 144.8 ± 95 ng/mL and 39.3 ± 85 ng/mL, respectively. The levels of serum-neutrophil gelatinase-associated lipocalin were higher in those ventilated mechanically, compared to self-breathing patients. Although urineneutrophil gelatinase-associated lipocalin levels were higher among mechanically ventilated patients than the controls, the difference was not statistically significant.

CONCLUSION

Based on our study findings, we consider that neutrophil gelatinase-associated lipocalin may be a useful biomarker for emerging lung injuries due to mechanical ventilation in critically ill children and deserves to be investigated.

Urinary biomarkers as point-of-care tests for predicting progressive deterioration of kidney function in congenital anomalies of kidney and urinary tract: trefoil family factors (TFFs) as the emerging biomarkers

BACKGROUND

Children with congenital anomalies of kidney and urinary tract (CAKUT) are at high risk of progressive deterioration of kidney function and further developing stage 5 chronic kidney disease (CKD 5), even after a successful surgery. This prospective study was designed to determine whether urinary biomarkers can predict progressive deterioration of kidney function in children with CAKUT.

METHODS

The study included 50 consecutive children, aged < 14 years, who were diagnosed with congenital uropathies (PUV, VUR, and PUJO) and 20 age-matched controls. Examination of four urinary biomarkers, i.e., trefoil family factors (TFF) 1 and 3, neutrophil gelatinase-associated lipocalin (NGAL) and microalbuminuria (MALB) was done at the beginning of follow-up. Kidney function was assessed, at the beginning and after 12-months of follow-up, by technetium-99m diethylene triamine pentaacetic acid (DTPA) and technetium-99m dimercaptosuccinic acid (DMSA) scans. Progressive deterioration in the kidney function was defined as a fall in the GFR from ≥ 60 to < 60 ml/min/1.73 m² on comparing the baseline and latest DTPA scans; and/or new-onset cortical scar/scars or increase in the size of previous scar/scars on serial DMSA scans. Group 1 and group 2 included children without and with progressive functional deterioration respectively.

RESULTS

The median (IQR) age of children with CAKUT and controls was 3 (1.5-5) and 2.3 (1.2-3.6) years, respectively, and showed no significant difference (p = 0.29). Median concentrations of TFF1, TFF3, NGAL, and microalbumin in patients were 44.5, 176.5, 281.2, and 15.5 mcg/gCr, respectively, and were significantly elevated as compared to controls (p < 0.05). Children belonging to group 2 had significantly higher concentration of biomarkers as compared to those in group 1. TFF3 was found have the highest AUC (0.9198) on ROC curve for predicting progressive functional deterioration.

CONCLUSION

Urinary TFFs, NGAL, and microalbumin significantly correlate with progressive deterioration of kidney function in children harboring CAKUT. TFF3, with the strongest prediction of functional deterioration, is an emerging peptide showing sufficient potential to be included in the biomarker panel. Graphical abstract.

Biomarkers in urinary tract infections - which ones are suitable for diagnostics and follow-up?

Introduction: Urinary tract infections (UTIs) are one of the most common infections worldwide. Under special circumstances, clinicians must rely on laboratory findings, which might have a weak predicting value, misguiding the practitioners and leading to incorrect diagnosis and overuse of antibiotics. Therefore, there is an urgent need for reliable biomarkers in UTIs. Methods: We performed a literature search for biomarkers used in UTIs from January 1999 until May 2020. We used "urinary tract infection" and "biomarker" as the main key words in the PubMed, Medline and Cochrane databases. After peer review, we excluded the duplicates and identified the suitable articles, from which we collected the data and divided the available biomarkers into 5 groups: i) conventional markers; ii) promising, thoroughly studied biomarkers; iii) promising biomarkers that need further studies; iv) biomarkers of unknown significance; v) controversial, not useful markers. Results: We found 131 articles, mostly from the paediatric population. Neutrophil gelatinase-associated lipocalin (NGAL) and interleukins (IL) have a leading role in diagnosing and differentiating UTIs based on a lot of observational, comparative trials. Heparin Binding Protein (HBP), Lactoferrin (LF), Heat-Shock Protein-70 (HSP-70), Human Defensin-5 (HD-5), Lipopolysaccharide Binding Protein (LBP) and mass spectrometry studies are promising, but confirming data are lacking. The measurable components of the innate immune system and local host cell response could be appropriate biomarkers, but their significance is currently unknown. Conclusions: Conventional biomarkers for UTIs have low specificity. The use of urinary NGAL and interleukins could improve the sensitivity and specificity of laboratory diagnosis of UTIs.

Discriminatory Precision of Neutrophil Gelatinase-Associated Lipocalin in Detection of Urinary Tract Infection in Children: a Systematic Review and Meta-Analysis

INTRODUCTION

There is a significant discrepancy between studies on diagnostic precision of neutrophil gelatinase-associated lipocalin (NGAL) in diagnosis of urinary tract infection (UTI). Therefore, the present systematic review and meta-analysis was designed to assess the diagnostic value of NGAL in diagnosis of UTI in children and adolescents.

METHODS

An extensive search was performed on Medline, Embase, Scopus and Web of Science databases by the end of 2019. Two independent researchers screened and summarized the data. Discriminatory precision of urinary and serum NGAL was assessed by reporting area under the curve, sensitivity, specificity and diagnostic odds ratio with 95% confidence interval (95% CI).

RESULTS

Data from 12 studies were included. The area under the curve of urinary and serum NGAL for diagnosis of UTI in children and adolescents at the best cut-off point (between 30-39.9 ng/ml) was 0.95 (95% CI: 0.93 to 0.97) and 0.83 (95% CI: 0.80 to 0.86), respectively. Sensitivity, specificity and diagnostic odds ratio on urinary NGAL at these cut-off points were 0.89 (95% CI: 0.64 to 0.97), 0.89 (95% CI: 0.71 to 0.97) and 67 (95% CI: 5 to 891), respectively. Sensitivity, specificity and diagnostic odds ratio of serum NGAL in UTI detection were 0.85 (95% CI: 0.70 to 0.90), 0.81 (95% CI: 0.69 to 0.88) and 9.53 (95% CI: 1.52 to 59.65), respectively.

CONCLUSION

The present meta-analysis showed that urinary NGAL had a high diagnostic value in detection of UTI in children and adolescents with an optimum cut-off point in the range of 30-39.9 ng/ml.

Identification of clinical and urine biomarkers for uncomplicated urinary tract infection using machine learning algorithms

Women with uncomplicated urinary tract infection (UTI) symptoms are commonly treated with empirical antibiotics, resulting in overuse of antibiotics, which promotes antimicrobial resistance. Available diagnostic tools are either not cost-effective or diagnostically sub-optimal. Here, we identified clinical and urinary immunological predictors for UTI diagnosis. We explored 17 clinical and 42 immunological potential predictors for bacterial culture among women with uncomplicated UTI symptoms using random forest or support vector machine coupled with recursive feature elimination. Urine cloudiness was the best performing clinical predictor to rule out (negative likelihood ratio [LR−] = 0.4) and rule in (LR+ = 2.6) UTI. Using a more discriminatory scale to assess cloudiness (turbidity) increased the accuracy of UTI prediction further (LR+ = 4.4). Urinary levels of MMP9, NGAL, CXCL8 and IL-1β together had a higher LR+ (6.1) and similar LR− (0.4), compared to cloudiness. Varying the bacterial count thresholds for urine culture positivity did not alter best clinical predictor selection, but did affect the number of immunological predictors required for reaching an optimal prediction. We conclude that urine cloudiness is particularly helpful in ruling out negative UTI cases. The identified urinary biomarkers could be used to develop a point of care test for UTI but require further validation.

Diagnostic accuracy of urine neutrophil gelatinase-associated lipocalin and urine kidney injury molecule-1 as predictors of acute pyelonephritis in young children with febrile urinary tract infection

Introduction

We assessed whether two urinary biomarkers of acute kidney injury, neutrophil gelatinase associated lipocalin (uNGAL) and kidney injury molecule-1 (uKIM-1), can be useful for predicting acute pyelonephritis (APN) in children aged 1-24 months with the first febrile urinary tract infection (UTI).

Material and methods

A prospective study included 54 children divided into two groups (24 with APN, 30 with lower UTI), according to the dimercaptosuccinic acid (DMSA) renal scintigraphy results. Laboratory tests: uNGAL, uKIM-1, procalcitonin (PCT), C-reactive protein (CRP), white blood count (WBC) were performed.

Results

We did not find significant differences in normalized and non-normalized values of uNGAL and uKIM-1 in children with APN and lower UTI. Positive correlations were determined between uNGAL and pyuria (r = 0.28, p < 0.05) and between uNGAL/uCr and uKIM-1/uCr (r = 0.53, p < 0.001) in the all UTI groups. Univariate logistic regression analysis demonstrated that only PCT (p < 0.0001) and CRP (p < 0.05) were important diagnostic factors of APN. Receiver operating curve (ROC) analysis showed good diagnostic profiles of PCT with the best cut-off value of 1.66 ng/ml and of CRP with the best cut-off value of 4.3 mg/dl for predicting APN (area under the curve [AUC]: 0.894 and 0.719, sensitivity: 75% and 96%, specificity: 93% and 43%, respectively).

Conclusions

uNGAL and uKIM-1 are not effective diagnostic markers for APN in young children with febrile UTI and cannot be used in clinical practice to differentiate APN from lower UTI.

Serum neutrophil gelatinase-associated lipocalin for predicting acute pyelonephritis in infants with urinary tract infection

Introduction

Fever and elevated inflammatory markers have been used for diagnosis of acute pyelonephritis (APN) in infants with urinary tract infection (UTI).

The aim of the study was to compare the usefulness of serum neutrophil gelatinase-associated lipocalin (sNGAL) with inflammatory markers for predicting APN in infants with UTI.

Material and methods

The prospective study included 46 infants with a first episode of UTI, divided into two groups (APN 23, lower UTI 23), according to the DMSA scan results. The following laboratory tests were performed: sNGAL, PCT, CRP, WBC, and ESR.

Results

Significantly elevated levels of sNGAL, PCT, CRP, and ESR were observed in infants with APN compared to those with lower UTI. Higher sNGAL, CRP, and ESR values, presence of fever, and longer duration of fever before antibiotic treatment were associated with APN [odds ratio (OR) 1.02, 1.27, 1.03, 13.46, 2.12, respectively]. Receiver operating characteristic (ROC) analysis showed better diagnostic profiles for sNGAL, PCT, and CRP than for ESR for predicting APN [area under the curve (AUC) 0.808, 0.819, 0.841, and 0.750, respectively]. The appropriate cut-off values of sNGAL, PCT and CRP were 100.8 ng/ml, 0.15 ng/ml, 5.3 mg/dl (all sensitivity and specificity 82.6%), and that of ESR was 40 mm/h (sensitivity 78.3%, specificity 60.9%).

Conclusions

sNGAL shows similar usefulness as PCT and CRP for predicting APN in infants with UTI, the diagnostic value of ESR is smaller, and WBC is not useful at all. The presence of fever and longer duration of fever are important predictors of APN in infants with UTI.

Plasma Neutrophil Gelatinase-Associated Lipocalin as a Predictor of Renal Parenchymal Involvement in Infants With Febrile Urinary Tract Infection: A Preliminary Study

BACKGROUND

Urinary tract infection (UTI) is the most common bacterial infection in infants. Renal parenchymal involvement is an important prognostic factor; however, early detection of parenchymal involvement in UTI may be difficult during infancy. This study aimed to assess whether a recently established biomarker of UTI, neutrophil gelatinase-associated lipocalin (NGAL), can serve as a useful marker for the detection of cortical defects (CD) and to determine the appropriate diagnostic cut-off value of NGAL in infants with febrile UTI.

METHODS

Infants hospitalized for febrile UTI were divided into two groups according to the presence of cortical defects on dimercaptosuccinic acid (DMSA) scintigraphy. Among 64 enrolled infants, 43 (67%) had CD (UTI-CD) and 21 (33%) had no CD (UTI-ND). The white blood cell count, C-reactive protein, and plasma NGAL (pNGAL) levels were determined before antibiotic therapy and compared between the two groups.

RESULTS

pNGAL level was significantly higher in the UTI-CD group than in the UTI-ND group (340 μg/L vs 214 μg/L, P=0.002). Multivariate analysis showed that pNGAL level was the only independent predictor of CD (odds ratio 2.759, P=0.039). In the ROC curve analysis, pNGAL showed the highest area under the curve (0.745; 95% confidence interval, 0.561-0.821; P=0.014). The appropriate cut-off value of pNGAL was 267 μg/L (sensitivity, 72.1%; specificity, 71.4%).

CONCLUSIONS

pNGAL was found to be a useful marker for early prediction of renal parenchymal involvement in infants with febrile UTI.

Diagnostic accuracy of urinary biomarkers in infants younger than 3 months with urinary tract infection

Purpose

The aim of this study was to evaluate the diagnostic accuracy of urinary biomarkers, such as neutrophil gelatinase-associated lipocalin (uNGAL) and β-2 microglobulin (uB2MG), in early detection of urinary tract infection (UTI) in infants aged <3 months with fever.

Methods

A total of 422 infants aged <3 months (male:female=267:155; mean age, 56.4 days), who were admitted for fever, were retrospectively included in this study. We compared uNGAL and uB2MG between the UTI and non-UTI groups at the time of admission. The sensitivity, specificity, accuracy, and area under the curve (AUC) of uNGAL and uB2MG for use in diagnosing UTI were assessed.

Results

Among 422 patients, 102 (24.2%) were diagnosed with UTI. Levels of uNGAL were higher in the UTI group than in the non-UTI group (366.6 ng/mL vs. 26.9 ng/mL, P<0.001). Levels of uB2MG were not different between the 2 groups. Multivariate analysis revealed that uNGAL was an independent predictive factor for UTI (P=0.033). The sensitivity, specificity, and accuracy were 90.2%, 92.5%, and 91.9% for uNGAL, and 48.0%, 43.8%, and 44.8% for uB2MG, respectively. AUC of uNGAL was 0.942 and that of uB2MG was 0.407.

Conclusion

Accuracy of uNGAL in the diagnosis of UTI is high in febrile infants aged <3 months. uNGAL can help in the early diagnosis and treatment of UTI in infants.

Urinary Neutrophil Gelatinase-Associated Lipocalin for the Diagnosis of Urinary Tract Infections

OBJECTIVES

To determine the accuracy of the novel biomarker urinary neutrophil gelatinase-associated lipocalin (uNGAL) to diagnose urinary tract infections (UTIs) in febrile infants and young children.

METHODS

Prospective cross-sectional study of febrile infants <3 months ( ≥ 38.0°C) and children 3 to 24 months (≥ 39.0°C) evaluated for UTIs. uNGAL levels, urinalysis, Gram-stain and culture were obtained. UTI was defined by colony counts.

RESULTS

Of 260 patients, 35 (13.5%) had UTIs. Median uNGAL levels were 215.1 ng/mL (interquartile range: 100.3-917.8) and 4.4 ng/mL (interquartile range: 1.6-11.8) in the groups diagnosed with and without UTIs, respectively. The area under the receiver-operating characteristic curve for uNGAL was 0.978 (95% confidence interval [CI]: 0.948-1.000). At a threshold uNGAL level of 39.1 ng/mL, sensitivity was 97.1% (95% CI: 83.4-99.9) and specificity was 95.6% (95% CI: 91.7-97.7). uNGAL had higher sensitivity than the combination of leukocyte esterase (in trace or greater amounts) or nitrite (+) (97.1%, 95% CI: 83.4-99.9 vs 74.3%, 95% CI: 56.4-86.9), with similar specificity (95.6%, 95% CI: 91.7-97.7 vs 97.3%, 95% CI: 94.0-98.9). uNGAL had higher sensitivity than Gram-stain (97.1%, 95% CI: 83.4-99.9 vs 74.3%, 95%: CI: 56.4-86.9), with similar specificity (95.6%, 95% CI: 91.7-97.7 vs 100.0%, 95% CI: 97.9-100.0).

CONCLUSIONS

uNGAL has substantial accuracy to identify those with and without UTIs in infants and young children. Further studies will need to confirm our findings and determine if uNGAL is a more cost-effective test than standard screening tests.

The role of novel biomarkers in childhood idiopathic nephrotic syndrome: a narrative review of published evidence

Two histological subtypes of idiopathic nephrotic syndrome are commonly recognized in children, namely minimal change nephropathy and focal segmental glomerulosclerosis. Children with minimal change nephropathy (the majority of whom are steroid-sensitive) and focal segmental glomerulosclerosis (the majority of whom are steroid-resistant) require early identification in order to ensure appropriate therapeutic intervention and better outcome. Although renal biopsy and histology remain the ideal diagnostic steps to identify these histological subtypes, reports indicate that serum and urinary biomarkers are now being utilized in the investigation of childhood idiopathic nephrotic syndrome. This paper aims to review the diagnostic and prognostic utility of novel biomarkers in childhood idiopathic nephrotic syndrome and to highlight their role in differentiating steroid-sensitive nephrotic syndrome (SRNS) from steroid-resistant nephrotic syndrome (SSNS). Using the terms “idiopathic nephrotic syndrome,” “children,” and “biomarkers” the PubMed database was searched for relevant studies related to the topic. Biomarkers such as adiponectin, neopterin, β2-microglobulin, and N-acetyl-β-D glucosaminidase were reported as diagnostic markers. In addition to neopterin and N-acetyl-β-D glucosaminidase, urine vitamin D-binding protein and α1β-glycoprotein were shown to differentiate SRNS from SSNS while N-acetyl-β-D glucosaminidase and β2-microglobulin could predict steroid responsiveness and renal outcome in SRNS. Although progress has been made in demonstrating the diagnostic and prognostic utility of these biomarkers, their limited availability in most laboratories has precluded a complete paradigm shift from the conventional renal biopsy. Nevertheless, further longitudinal studies are required to establish their usefulness as noninvasive predictors of disease response to immunosuppressive therapy.

Neutrophil gelatinase-associated lipocalin: utility in urologic conditions

Neutrophil gelatinase-associated lipocalin (NGAL) is best known as a non-invasive early marker of acute kidney injury (AKI). However, recent published reports have described additional utility of both plasma NGAL (pNGAL) and urine NGAL (uNGAL) in various pathologic conditions within the pediatric urinary tract, including urinary tract infection, vesicoureteral reflux (VUR), renal scarring, and obstructive uropathy. These two forms of NGAL have different applications related to their mechanisms of upregulation: pNGAL can serve as a marker of systemic inflammatory conditions, whereas uNGAL is specific for insults to the renal epithelium. Therefore, pNGAL has good predictive accuracy in systemic inflammation associated with pyelonephritis and renal damage, while uNGAL is an effective marker for identifying infection within the genitourinary environment as well as subclinical renal damage as a result of scarring or obstruction. Continued work should focus on the effect of trending NGAL values in patients with pyelonephritis, VUR, and hydronephrosis, to determine if longitudinal NGAL patterns have value in predicting adverse outcomes.

Neutrophil Gelatinase-Associated Lipocalin: A Biomarker for Early Diagnosis of Urinary Tract Infections in Infants

Early diagnosis of urinary tract infection (UTI) is challenging in infants due to unspecific symptoms, difficulty in urine collection and possible contamination. The aim of this study was to assesses the usefulness of serum and urine neutrophil gelatinase-associated lipocalin (sNGAL and uNGAL, respectively) in the diagnosis of febrile and non-febrile UTI in infants. This prospective observational study enrolled 66 infants with the first episode of UTI and 18 healthy controls. At the time of enrollment, sNGAL, uNGAL, urinalysis, urine culture, white blood cell count (WBC), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), procalcitonin (PCT), and serum creatinine (sCr) were assessed. We found that, on average, both sNGAL and uNGAL levels were significantly higher in febrile UTI, compared to non-febrile UTI and controls. In turn, the mean sNGAL level, but not uNGAL, was significantly higher in the non-febrile UTI group compared to controls. sNGAL positively correlated with WBC, CRP, ESR and PCT, and uNGAL with CRP and leukocyturia. The receiver operating curves (ROC) demonstrate that the optimum cut-off of 76.2 ng/ml for sNGAL (sensitivity 92.9%, specificity 94.4%, and the area under the curve (AUC) of 0.98) and of 42.2 ng/ml for uNGAL (sensitivity 73.8%, specificity 72.2%, and AUC of 0.76) for diagnosing febrile UTI and 39.0 ng/ml for sNGAL (sensitivity 83.3%, specificity 55.6%, and AUC of 0.70) for diagnosing non-febrile UTI. In conclusion, serum NGAL is an excellent marker for the early diagnosis of febrile UTI, with sensitivity and specificity higher than those of urine NGAL. Diagnostic sensitivity of serum NGAL is smaller in non-febrile infants suffering from UTI, and urine NGAL is not useful for this purpose at all.

Neutrophil gelatinase-associated lipocalin and innate immune responses to bacterial infections

Neutrophil gelatinase-associated lipocalin (NGAL), an essential component of the antimicrobial innate immune system, is present in neutrophils and multiple other tissues. It prevents iron acquisition by microorganisms by sequestering iron-loaded bacterial siderophores. NGAL also modulates neutrophil functions. Its production is inducible following Toll-like receptor 4 activation and release of pro-inflammatory cytokines. NGAL is employed clinically in the diagnosis of acute kidney injury and may be useful in general in the differential diagnosis of a bacterial-mediated infectious process. Elevated levels of NGAL have been detected in the blood of patients with bacterial urinary tract infection, community-acquired pneumonia, sepsis, as well as in the cerebrospinal fluid and peritoneal fluid of patients with bacterial meningitis and peritonitis. Some bacteria have developed resistance to NGAL-mediated iron sequestration by production of modified siderophores that are not recognized by NGAL.