Variation of pNGAL values in a batch of pediatric patients with chronic kidney disease from northeastern Romania

Introduction

Chronic kidney disease (CKD) incidence and its mortality rates have increased in pediatric patients over the past 20 years⁽¹⁾. It is estimated that the prevalence of all-stage chronic kidney disease may be as high as 1% of the pediatric population⁽¹⁾. This places an increased financial burden on the medical system, especially at later CKD stages. Early diagnosis of chronic kidney disease allows for strategies to slow down the disease progression⁽²⁾. Serum creatinine clearance remains the gold standard of monitoring CKD progression. It is, however, prone to a degree of bias, because it is an indirect method of appreciation of renal function, and it can be influenced by muscular mass differences and metabolic modifications, some of which can be caused by CKD progression itself^(2,3). The need for a new more specific biomarker is evident. Of all suggested biomarkers, neutrophil gelatinase-associated lipocalin (NGAL) has shown promise^(4-7). NGAL is a 25-kDA metalloproteinase. It was initially studied in adults for monitoring early kidney function loss in patients with coronary bypass^(6-8). In pediatric studies, it showed earlier modifications than creatinine clearance in patients with contrast-related kidney disease and in critically ill children admitted in pediatric intensive care units (PICU)^(9-11). NGAL has also shown promise in monitoring CKD patients with vesicoureteral reflux⁽¹²⁾. Pediatric studies regarding CKD have some physiological limitations^(12-14), but also the fact that there are few patients who agree to be included in the studies, and there is no consensus regarding the cutoff value of NGAL^(12,15,16).

Objective

Our study aimed to observe the pediatric NGAL (pNGAL) values variation in patients with different stages and causes of CKD in a pediatric population from the north­eastern part of Romania.

Materials and method

Inclusion criteria

• Age: 0-18 years old.
• Diagnosis or history of CKD.

Exclusion criteria

• Acute kidney disease (AKI) at admission.
• History of inflammatory diseases outside CKD.
• Increased leukocyte count.
• Lack of consent to participate in the study.

Blood samples were collected and centrifuged, then stored initially at -20ºC, and afterwards stored at -80ºC for up to six months. ELISA assays were performed as per manufacturer recommendations.

Patients’ data were collected, included and introduced in Microsoft Excel. All statistical interpretations were performed in Microsoft Excel (Pearson correlation coefficient, t statistic test, p values etc.).

Results

Seventeen patients were included between January 2021 and March 2023. CKD etiologies included IgA glomerulonephritis with crescents, vesicoureteral reflux (degrees 2 to 4) with reflux nephropathy, neurogenic bladder with reflux nephropathy, atypic hemolytic-uremic syndrome, and nephrotic syndrome, both corticoresistant and corticodependent.

The patients’ distribution regarding age, serum creatinine, eGFR (calculated with the pediatric Schwartz formula) and pNGAL values can be observed in Table 1.

There is an increase of pNGAL values concentration for the same age of chronic kidney disease, as shown in Figure 1.

There was a negative correlation between pNGAL concentration and creatinine clearance values (Pearson correlation coefficient r = -0.54834; p=0.02266; p<0.05). The pNGAL concentration distribution compared to creatinine clearance values is represented in Figure 2.

Discussion

Patients’ distribution in this study is rather unnatural. There are 13 patients in stage 1 CKD, two patients in stage 3 CKD, one patient in stage 4 CKD, and one patient in stage 5 CKD. There are no patients in stage 2. This is a limitation of the study, that it can also promote some confounding factors. Another observation is that creatinine clearance for stage 1 patients varies from 93 to 251 ml/1.73 m². Various etiologies of chronic kidney disease were introduced in the study, both glomerular and nonglomerular. 

Our study also reflects the general consensus that nonhomogenous etiologies of CKD will yield different values of NGAL and that the usefulness of NGAL must be assessed to each etiology of chronic kidney disease^{(12-14,17-22)}.

The negative correlation we found between pNGAL concentration and creatinine clearance values is smaller than the one found in the study by Xiang et al. from 2014 (r = -0.54834, p=0.02266, p<0.05, compared to r = -0.739, p<0.001)⁽²³⁾. The source of difference is most likely due to physiological differences in adults compared to children and due to the number of patients we could include in the study (17 children compared to 240 adults) and the different stages of chronic kidney disease. It is, however, in consensus with the study of Bolignano et al. (2009), who found that serum and urinary levels of NGAL were inversely proportional to the GFR level and even more so with stage 1-3 CKD⁽²⁴⁾.

We also found a positive correlation of the pNGAL values respective to age for the same stage of CKD (Pearson correlation coefficient r=0.656816; p=0.014734; p<0.05). This is not in concurrence with other studies that promote pNGAL as an independent marker for kidney injury^(17-26). There is a study by Bellos et al.⁽²⁷⁾ (2018) which suggests that, in children, smaller kidneys lack sufficient renal tubular cells with residual regenerative capacity to secrete enough NGAL as an injury response. By contrast, our study inclu­ded older children. We believe that this result may be due to the variation of CKD etiology, as one of the older patients had underlying IgA nephropathy with the highest value of p-NGAL for stage 1 CKD, high erythrocyte sedimentation rate, but no leukocytosis. There was no correlation between erythrocyte sedimentation rate and pNGAL values. Further studies, with an increased number of patients and similar CKD etiologies and stages, must be performed to evaluate the correlation between pNGAL values and age.

Conclusions

pNGAL can be used as an adjuvant biomarker in monitoring CKD patients regardless of stage (Pearson r correlation coefficient r = - 0.55834; p=0.02).

We found a positive correlation of the pNGAL values respective to age for the same stage of CKD (Pearson correlation coefficient r = 0.656816; p=0.014734; p<0.05). This is not in concurrence with other studies that promote pNGAL as an independent marker for kidney injury. Further studies with an increased number of patients and similar CKD etiologies and stages must be performed to evaluate the correlation between pNGAL values and age.

Urinary NGAL and other biomarkers, such as cystatin C, kidney injury molecule 1 (KIM-1), L-fatty acid binding protein (L-FABP) or insulin-like growth factor-binding protein 7 (ILFBP-7) x tissue inhibitor of metalloproteinase 2 (TIMP-2), can be added to the testing panel in order to limit the confounding factors and improve monitorization for disease progression^(28,29).

NGAL shows promise in the monitorization of CKD, but the usefulness of NGAL must be assessed to each etio­logy of chronic kidney disease.   

Corresponding author: Aurelian-Bogdan Stana E-mail: aurelian.stana@umfiasi.ro

Conflict of interest: none declared.

Financial support: none declared.

This work is permanently accessible online free of charge and published under the CC-BY licence.