Factors limiting usefulness of serum and urinary NGAL as a marker of acute kidney injury in preterm newborns

Figures & data

Table 1. Characteristics of all premature infants and distinguished subgroups according to the grade of maturity (means with 95% confidence intervals).

	All [N = 57]	≤29 hbd [N = 25]	≥30 hbd [N = 32]	Statistical significance
Gender (M/F)	35/22	18/7	17/15	0.15
Gestational age (weeks)	30 (29–31)	27 (26–28)	33 (32–34)	<0.001
Birth weight (g)	1536 (1365–1708)	1029 (895–1163)	1932 (1735–2131)	<0.001
Apgar 5′ (pts)	6.3 (5.7–7.0)	4.8 (4.0–5.5)	7.5 (6.7–8.3)	<0.001
Day of life	5 (3–8)	4 (2–5)	7 (3–11)	0.19
NTISS 1st week (pts)	20 (19–23)	24 (21–26)	18 (15–22)	0.02
NTISS 2nd week (pts)	16 (14–19)	21 (18–23)	13 (9–16)	<0.001
NTISS 4th week (pts)	9 (6–12)	9 (6–14)	9 (4–13)	0.72
WBC 1st week (10^3/μL)	14.9 (12.3–17.5)	17.6 (13.4–21.8)	12.6 (9.4–15.7)	0.05
WBC 2nd week (10^3/μL)	14.5 (12.9–16.2)	16.7 (15.5–19.9)	12.7 (11.3–14.2)	0.02
WBC 4th week (10^3/μL)	11.3 (10.0–12.5)	10.6 (8.3–12.9)	11.7 (10.2–13.3)	0.38
PLT 1st week (10^3/μL)	181 (154–209)	152 (115–189)	206 (166–247)	0.05
PLT 2nd week (10^3/μL)	289 (245–333)	227 (169–285)	340 (278–402)	0.01
PLT 4th week (10^3/μL)	344 (292–396)	278 (222–334)	394 (316–474)	0.02
CRP 1st week (mg/dL)	9.4 (3.5–15.3)	8.7 (0.3–17.6)	10.7 (0.5–21.0)	0.79
CRP 2nd week (mg/dL)	16.0 (4.5–27.5)	14.8 (2.7–26.9)	16.8 (0.5–34.6)	0.87
CRP 4th week (mg/dL)	10.5 (1.0–19.9)	5.6 (1.6–9.5)	14.4 (0.1–31.3)	0.36
PCT 1st week (ng/mL)	10.6 (4.6–16.6)	10.8 (1.6–20.1)	10.3 (2.1–18.6)	0.93
PCT 2nd week (ng/mL)	3.4 (0.1–7.7)	2.4 (0.1–6.1)	4.1 (0.2–0.9)	0.71
PCT 4th week (ng/mL)	1.1 (0–2.6)	0.4 (0.1–0.6)	1.5 (0–3.9)	0.44
Urea 1st week (mg/dL)	40.8 (34.5–47.1)	53.0 (42.5–63.4)	31.4 (25.2–37.5)	0.003
Urea 2nd week (mg/dL)	24.2 (19.4–28.9)	30.2 (20.7–39.5)	19.6 (15.6–23.6)	0.02
Urea 4th week (mg/dL)	19.3 (14.6–29.3)	15.6 (10.7–20.6)	21.9 (14.5–29.3)	0.19

Note: M: male; F: female; NTISS: Neonatal Therapeutic Intervention Scoring System; WBC: white blood cell; PLT: platelet count; CRP: C-reactive protein; PCT: procalcitonin.

Table 2. Characteristics of renal parameters in all premature infants and distinguished subgroups according to the grade of maturity (means with 95% confidence intervals).

	All [N = 57]	≤29 hbd [N = 25]	≥30 hbd [N = 32]	Statistical significance
UO1st week (mL/kg/h)	5.4 (4.7–6.1)	6.0 (4.9–7.2)	4.8 (4.0–5.7)	0.08
UO 2nd week (mL/kg/h)	5.7 (5.0–6.5)	6.3 (5.1–7.5)	5.1 (4.4–5.9)	0.09
UO4th week (mL/kg/h)	4.6 (4.0–5.3)	5.0 (3.9–6.0)	4.1 (3.2–5.1)	0.22
sCr 1st week (mg/dL)	0.98 (0.92–1.05)	1.05 (0.95–1.14)	0.93 (0.84–1.02)	0.07
sCr 2nd week (mg/dL)	0.75 (0.66–0.84)	0.81 (0.68–0.95)	0.70 (0.58–0.81)	0.16
sCr 4th week (mg/dL)	0.53 (0.48–0.59)	0.53 (0.42–0.64)	0.54 (0.47–0.60)	0.93
eGFR 1st week (mL/min)	14.9 (13.7–16.1)	12.4 (11.1–13.7)	17.0 (15.5–18.5)	<0.001
eGFR 2nd week (mL/min)	20.9 (19.0–22.7)	17.4 (14.9–20.0)	23.6 (21.4–25.9)	<0.001
eGFR 4th week (mL/min)	28.5 (25.7–31.3)	26.3 (22.7–29.9)	30.1 (26.0–34.3)	0.17
CystC 1st week (mg/L)	1.80 (1.65–1.95)	1.79 (1.53–2.04)	1.81 (1.61–2.01)	0.85
CystC 2nd week (mg/L)	1.82 (1.65–2.00)	1.76 (1.45–2.07)	1.87 (1.64–2.09)	0.57
CystC 4th week (mg/L)	2.01 (1.70–2.32)	1.75 (1.50–2.00)	2.11 (1.69–2.54)	0.28
sNGAL 1st week (ng/mL)	144 (107–180)	148 (90–207)	140 (90–190)	0.81
sNGAL 2nd week (ng/mL)	118 (82–154)	127 (69–185)	110 (61–160)	0.66
sNGAL 4th week (ng/mL)	100 (43–157)	76 (15–138)	114 (27–200)	0.53
uNGAL 1st week (ng/mL)	106 (59–153)	106 (66–146)	106 (24–188)	0.99
uNGAL 2nd week (ng/mL)	111 (73–149)	134 (73–194)	91 (40–142)	0.27
uNGAL 4th week (ng/mL)	83 (32–135)	63 (32–95)	96 (11–180)	0.54

Note: UO: urinary output; sCr: serum creatinine; eGFR: estimated glomerular filtration rate; CystC: cystatin C; sNGAL: serum NGAL; uNGAL: urinary NGAL.

Table 3. Univariate correlations between sNGAL and uNGAL values on the following points of time and selected parameters.

	NGAL
	1st Week		2nd Week		4th Week
	Serum	Urinary	Serum	Urinary	Serum	Urinary
NTISS	NS	R = 0.354	R = 0.383	R = 0.352	NS	NS
		p = 0.02	p < 0.01	p = 0.02
sCr	NS	NS	R = 0.311	NS	NS	NS
			p = 0.03
eGFR	NS	NS	R = −0.304	R = −0.259	NS	NS
			p = 0.03	p = 0.08
UO	NS	NS	NS	NS	NS	NS
WBC	R = 0.229	NS	R = 0.291	NS	NS	NS
	p = 0.08		p = 0.004
PLT	R = −0.268	NS	R = −0.350	R = −0.336	NS	NS
	p = 0.06		p = 0.005	p = 0.02
CRP	R = 0.311	R = 0.373	R = 0.394	R = 0.302	NS	NS
	p = 0.03	p = 0.011	p < 0.01	p = 0.05
PCT	R = 0.285	NS	R = 0.542	R = 0.478	NS	NS
	p = 0.07		p < 0.001	p = 0.003
BW	NS	R = −0.425	NS	R = −0.340	NS	R = −0.366
		p = 0.003		p = 0.02		p = 0.04
Apgar 5′	NS	NS	NS	NS	NS	NS
GA	NS	R = −0.278	NS	R = −0.289	NS	NS
		p = 0.05		p = 0.04
CystC	R = 0.285	NS	NS	NS	NS	NS
	p = 0.09

Note: NTISS: Neonatal Therapeutic Intervention Scoring System; sCr: serum creatinine; eGFR: estimated glomerular filtration rate; UO: urinary output; WBC: white blood cell; PLT: platelet count; CRP: C-reactive protein; PCT: procalcitonin; BW: birth weight; GA: gestational age; CystC: cystatin C.

Table 4. Multiple regression analysis including sNGAL and uNGAL as independent variables and gestational age, birth weight, 5 min Apgar score, serum creatinine, and alternatively CRP or PCT as an explanatory variables.

	sNGAL			uNGAL
	1st Week	2nd Week	4th Week	1st Week	2nd Week	4th Week
BW	NS	NS	NS	NS	NS	NS
GA	NS	NS	NS	NS	β = −0.211	NS
					p = 0.08
Apgar 5′	NS	NS	NS	NS	NS	NS
CRP	β = 0.301	β = 0.683	β = 0.638	NS	β = 0.659	β = 0.753
	p = 0.04	p < 0.001	p < 0.001		p < 0.001	p < 0.001
BW	NS	NS	NS	β = −0.341	β = −0.193	NS
				p = 0.08	p = 0.09
GA	NS	NS	NS	NS	NS	NS
Apgar 5′	NS	NS	NS	NS	NS	NS
PCT	β = 0.307	β = 0.817	β = 0.696	β = 0.293	β = 0.672	β = 0.759
	p = 0.06	p < 0.001	p < 0.001	p = 0.08	p < 0.001	p < 0.001

Note: sNGAL: serum NGAL; uNGAL: urinary NGAL; BW: birth weight; GA: gestational age; CRP: C-reactive protein; PCT: procalcitonin.