The prognostic value of neutrophil gelatinase-associated lipocalin in sepsis-associated acute kidney injury: A prospective observational study.

BACKGROUND: Sepsis is one of the most common triggering factors for acute kidney injury (AKI). The aim of the study is to evaluate the outcome in sepsis with AKI and determine the prognostic value of urinary neutrophil gelatinase-associated lipocalin (NGAL) in septicemic AKI.
MATERIALS AND METHODS: This prospective follow-up study was carried out over a period of 1 year after ethical clearance from the Institutional Ethics committee, a total 165 cases of septicemia were recruited, of which 15 patients were dropped out, 150 patients were identified suffering from septicemia defined as per the organ dysfunction criteria (according to third international consensus 2016) and patients of AKI defined as per the Kidney Disease Improving Global Outcomes 2012 criteria).
RESULTS: Out of 150 patients of septicemia enrolled in the study, only 38 (25.33%) suffering from AKI were classified as Group I and rest 112 (74.67%) patients of septicemia not suffering from AKI were classified as Group II. In total, 60.0% (90) patients were discharged from the hospital, rest of the patients (40%) expired. Mean duration of survival was higher in Group II (21.29 ± 1.89 days) as compared to Group I (13.67 ± 1.06 days). Cases with ≥121.90 urine NGAL, rate of mortality (41.7%), were higher as compared to alive patients discharged (34.4%).
CONCLUSION: Sequential organ failure assessment score, hospital stay, and mortality were high in septicemic patients with AKI as compared to sepsis without AKI. Survival of patients also not good with septic AKI, those patients who had high NGAL value had poor prognosis. Copyright:

INTRODUCTION

Sepsis is one of the most common triggering factors for acute kidney injury (AKI) in critically ill patients. In a prospective study, sepsis was recognized as the most important contributing factor for AKI, and the rate is approximately 50%.[1] Other studies reported that 40%–75% of AKI were associated with sepsis.[234] These patients generally had a poor prognosis when compared to septic non-AKI.[567] Therefore, early detection of septic AKI patients is of great importance to enable adequate treatment in these patients and improve their outcomes. AKI incidence rate and severity correlate with the severity of the underlying sepsis.[5]

Pathophysiology of Acute kidney injury is complex, it not only ischemic damage it varies according to etiological triggers.[8] Kidney injury might be a combination of immunologic, toxic, and inflammatory damage that may affect the microvasculature and the tubular cells.[9]

In the current clinical practice, AKI is diagnosed by measuring blood urea nitrogen (BUN) and serum creatinine, but it is well recognized that BUN and serum creatinine are insensitive and late indicators of AKI.[10] More recently, urine neutrophil gelatinase-associated lipocalin (uNGAL) has been considered more sensitive and specific test to detect AKI.[11] However, uNGAL is also a marker of systemic inflammation, since it is typically released by neutrophils upon activation.[12] Hence, it is extremely important to determine the relationship between uNGAL and septic AKI. The aim of this study is to evaluate the outcome in sepsis with AKI (in terms of sequential organ failure assessment [SOFA] score, morbidity, duration of hospital stay, and mortality) and determine the prognostic value of urinary NAGL in septicemic AKI.

MATERIALS AND METHODS

This prospective follow-up study was carried out over a period of 1 year in the Department of Internal Medicine, Nephrology Unit in collaboration with the Department of Pathology, King George's Medical University, Lucknow. Ethical clearance was obtained from the Institutional Ethics Committee, Research Cell, King George's Medical University, Lucknow, and after informed consent, a total of 165 cases of septicemia were recruited for the study, of which 15 patients were dropped out, 150 patients were identified suffering from septicemia defined as per the organ dysfunction criteria (according to the third international consensus 2016) and patients of AKI defined as per the Kidney Disease Improving Global Outcomes (KDIGO) 2012 criteria were enrolled for this study. Thus, 38 patients of septicemia with AKI and 112 patients of septicemia without AKI who fulfilling the inclusion criteria were enrolled in the study.

Patients with age group of >18 years, who were admitted in intensive care unit with evidence of sepsis, were included in this study. Patients who had end-stage renal disease, glomerular filtration rate <15 ml/min/m2, acute glomerulonephritis and acute interstitial nephritis, renal vasculitis or postrenal etiology for AKI, or who had renal transplant and on chronic dialysis therapy were excluded from the study.

AKI defined as per the KDIGO 2012.[13]

Increase in serum creatinine by ≥0.3 mg/dl (≥26.5 mol/L) within 48 h or increase in serum creatinine to ≥1.5 times from baseline or urine volume 0.5 ml/kg/h for 6 h. AKI is staged as, Stage 1: increase in serum creatinine by 1.5–1.9 times from baseline; or increase in serum creatinine by ≥0.3 mg/dL (≥26.5 mol/L); or urine output 0.5 ml/kg/h for 6–12 h, Stage 2: increase in serum creatinine by 2.0–2.9 times baseline; or urine output ≤ 0.5 ml/kg/h for 12 h, and Stage 3: increase in serum creatinine by 3.0 times from baseline; or increase in serum creatinine to 4.0 mg/dl (353.6 mol/L); or initiation of renal replacement therapy.

According to the third international consensus 2016, sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection.[14] Clinical criteria are suspected or documented infection and an acute increase of ≥2 SOFA points.[14] About 5 ml venous blood samples were obtained within the first 24 h of intensive care unit (ICU) admission and then every next day for 3 days from all patients and centrifuged at 5000 rpm for 10 min at room temperature, serum was separated for routine hematology biochemistry test. Urine samples were collected on day 1, either from spontaneous voids or from indwelling Foley catheters for urinalysis, and urine protein measurements as per the study protocols.

Automated blood cell analyzer (Abbott CELL-DYN Ruby Hematology Analyzer) was used for routine hematology testing, and an automated clinical biochemistry analyzer (Elitech Selectra PROM) for BUN, creatinine, electrolytes, serum bilirubin, and albumin testing. Enzyme-linked immunosorbent assay (ELISA) technique was used to measure urine NGAL (uNGAL) levels. A clean, morning midstream urine sample (5 mL) was collected into a sterile test tube and centrifuged at 5000 rpm for 15 min. The supernatant was transferred to an Eppendorf tube and stored at − 80°C until uNGAL was measured. A human NGAL ELISA kit (Epitope Diagnostics, Inc., San Diego, CA, USA) was used for estimation of uNGAL as per the manufacturer's protocol. Serum creatinine was measured by Jaffe's method and its normal range was 0.8–1.2 mg/dl.

SPSS 15 version IBM (SPSS Inc., 233 South Wacker Drive, 11th Floor, Chicago, IL, USA). Results were analyzed as mean ± standard deviation and percentiles or median (range) values. The independent samples t-test, and Chi-square and Mann–Whitney U-tests were used for comparison of the categorical and continuous variables. NGAL values, sepsis and non-AKI, and sepsis and AKI groups were evaluated and compared with by one-way analysis of variance. P < 0.05 was considered statistically significant.

RESULTS

Out of 150 patients of septicemia enrolled in the study, only 38 (25.33%) suffering from AKI were classified as Group I and rest 112 (74.67%) patients of septicemia not suffering from AKI were classified as Group II. Out of 38 (25.33%) septic AKI patients, 28.95% (11) Stage I AKI, 34.21% (13) Stage 2 AKI, and 36.84% (14) Stage III AKI were found on the basis of serum creatinine level observed every 3 days of duration [Table 1].

Table 1

Distribution of patients in two groups (septic acute kidney injury and septic nonacute kidney injury) and grade of acute kidney injury among septic acute kidney injury patients

Group	Description	Number of patients (n=150), n (%)	Grade of AKI	Number of patients (n=38), n (%)
Group I	Septic AKI	38 (25.33)	Stage I	11 (28.95)
			Stage II	13 (34.21)
			Stage III	14 (36.84)
Group II	Septic non-AKI	112 (74.67)

AKI: Acute kidney injury

Difference in SOFA score of patients of Group I (4.39 ± 1.13) and Group II (3.33 ± 0.86) was found to be statistically highly significant P < 0.001 [Table 2].

Table 2

Comparison of SOFA score among Group I and Group II

Group	n	Score minimum	Score maximum	Median	Mean±SD	P
Group I	38	3	7	4.00	4.39±1.13	0.001*
Group II	112	2	5	3.00	3.33±0.86
Total	150	2	7	4.00	3.60±1.04

Z=4.873 (Mann–Whitney U-test); *P<0.001 (significant). SD: Standard deviation, SOFA: Sequential organ failure assessment

60.0% (90) patients were discharged from the hospital, rest of the patients (40%) expired, though higher number of patients of Group II (sepsis without AKI) (61.61%) were discharged in uneventful condition as compared to Group I (sepsis with AKI) (55.26%) and difference was statistically not significant [Figure 1].

Figure 1

Comparison of outcomes among Group I and Group II. χ2 =0.476 (df = 1);P= 0.490

Out of 150 patients, 40.0% (60) expired; mortality rate was higher in Group I (44.7%) as compared to Group II (38.4%). Mean duration of survival was higher in Group II (21.29 ± 1.89 days) as compared to Group I (13.67 ± 1.06 days), but this difference was statistically not significant [Table 3 and Figure 2].

Table 3

Survival analysis for septic acute kidney injury and nonacute kidney injury septic population

Group	Total	Number of mortalities (%)	Mean survival time±SE (days)	P
Group I (septic AKI)	38	17 (44.7)	13.67±1.06	0.356
Group II (septic non-AKI)	112	43 (38.4)	21.29±1.89
Overall	150	60 (40.0)	18.68±1.70

Log-rank (Mantel–Cox) χ2=0.850; P=0.356 (NS). AKI: Acute kidney injury, SE: Standard error, NS: Not significant

Figure 2

Survival analysis for septic acute kidney injury and nonacute kidney injury septic population

Urinary NGAL level of patients of Group I (231.09 ± 64.03) was found to be significantly higher as compared to that of Group II (119.04 ± 32.57) [Table 4].

Table 4

Urine neutrophil gelatinase-associated lipocalin levels among Group I and Group II and association of grade of acute kidney injury with neutrophil gelatinase-associated lipocalin among septic acute kidney injury patients

Group	n	Range	Mean±SD	P	Grade	NGAL
						Range	Mean±SD
Group I	38	116.80-356.20	231.09±64.03	0.001*	Stage I (n=11)	146.70-308.40	231.05±57.65
					Stage II (n=13)	116.80-314.80	232.12±71.16
					Stage III (n=14)	148.60-356.20	230.16±66.60
					F, P	0.003; 0.997
Group II	112	64.30-221.60	119.04±32.57
Total	150	64.30-356.20	147.43±64.80

t=13.988; *P<0.001 (significant). SD: Standard deviation, NGAL: Neutrophil gelatinase-associated lipocalin

Out of All cases those who had uNGAL ≥121.90, rate of mortality (41.7%) was higher in these cases as compared to patients who were alive and discharged (34.4%) from the hospital [Table 5].

Table 5

Association of outcome with neutrophil gelatinase-associated lipocalin

	Number of alive patients (n=90), n (%)	Number of expired patients (n=60), n (%)	Statistical significance
			χ2	P
At cut off of NGAL value (≥121.90)	31 (34.4)	25 (41.7)	0.807	0.370

NGAL: Neutrophil gelatinase-associated lipocalin

DISCUSSION

In the present study, patients age ranged from 18 to 85 years and majority of patients in both the groups were ≤40 years of age. Although the mean age of patients of Group I (37.97 ± 18.50 years) was higher as compared to Group II (33.43 ± 17.83 years), the difference was nonsignificant. Another study also reported higher mean age of septic AKI patients as compared to septic non-AKI patients (P = 0.200).[15]

The present study result showed that advance age was much prone for development of AKI. Another author reported the mean age of septic AKI was 70 ± 13 years.[16]

In the present study, Group I had high SOFA score (mean 4.39) and more prone to develop AKI as compared to Group II (mean SOFA 3.00), and this difference was statistically significant (P < 0.001). Another study reported a significantly higher SOFA score in the septic AKI patients as compared to non-AKI sepsis (P < 0.01).[17]

In our study, hospital stay was significantly prolonged in septic AKI patients as compared to sepsis without AKI (mean value of 10.50 days in Group I vs. 7.64 days in Group II) (P = 0.011). Similarly, mortality was high in septic AKI group as compared to sepsis without AKI (44.74% in AKI group vs. 38.39% in non-AKI group) (P = 0.490). Similarly reported by another author where duration of hospital stay was higher in sepsis AKI group (24 ± 17) as compared to septic non-AKI group (18 ± 11). Similarly, mortality was high in septic AKI group 42 (67%) as compared to septic non-AKI group 16 (24%).[16]

In sepsis, the kidney is one of the most commonly affected organs almost 47.0% AKI cases are associated with sepsis.[1]

Previous studies showing increased concentration of NGAL level in sepsis regardless of the presence or absence of AKI.[15] This specific characteristics make it difficult to use NGAL to identify AKI associated with sepsis. While another study demonstrated that NGAL seems to be a useful predictor of AKI in patients with sepsis, although NGAL concentration did not differ significantly between AKI and non-AKI patients.[11] In our study, NGAL value was high in patients with septicemia-associated AKI as compared to septicemia without AKI. Day 1 urinary NGAL was good prognostic marker in septic patients with AKI. Similarly, another author also reported higher value of urinary NGAL in AKI with sepsis as compared to sepsis without AKI and they also found good predictive power of NGAL for identifying AKI with sepsis.[18]

Among cases with ≥ 121.90 uNGAL, prognosis was poor; number of deceased was higher (41.7%) as compared to number of alive and discharge (34.4%).

The values of urine NGAL were measured from sample collected on day 1. Patient developing AKI (Group I) had significantly higher value of uNGAL (231.09 ± 64.03 vs. 119.04 ± 32.57) even on day 1 (P < 0.001). One author suggested that plasma NGAL was raised in patients with systemic inflammatory response syndrome, severe sepsis, and septic shock and should be used with caution as a marker of AKI in ICU patients with septic shock, and suggested that uNGAL is more useful in predicting AKI, as the levels are not elevated in septic patients without AKI.[15]

CONCLUSION

Outcome of the patients in terms of hospital stay and mortality was high in septicemic patients with AKI as compared to sepsis without AKI. Those patients who had high NGAL value had poor prognosis. Significant difference in mean value of NGAL was found between septic AKI and nonseptic AKI. Urinary NGAL concentration was associated with severity of disease and has good prognostic value.

Research quality and ethics statement

The authors of this manuscript declare that this scientific work complies with reporting quality, formatting, and reproducibility guidelines set forth by the EQUATOR Network. The authors also attest that this clinical investigation was determined to require Institutional Ethics Committee, Research Cell, King George's Medical University, Lucknow and appropriate approval (84th ECM II-B-Thesis) was granted by the Research Cell, King George's Medical University, Lucknow.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Ethical conduct of research

This study was approved by the Institutional Review Board / Ethics Committee. The authors followed applicable EQUATOR Network (http://www.equator-network.org/) guidelines during the conduct of this research project.