Blood Urea Nitrogen to Serum Albumin Ratio in the Prediction of Acute Kidney Injury of Patients with Rib Fracture in Intensive Care Unit

Figures & data

Figure 1 Study flow diagram in the present study.

Table 1 Comparisons of Baseline Characteristics Between the Original Cohort, Matched Cohort and Weighted Cohort

Covariates	Original Cohort			Matched Cohort			Weighted Cohort
	Low BAR	High BAR	P	Low BAR	High BAR	P	Low BAR	High BAR	P
N	526	427		197	197		189.8	192.9
Age, years	53.5 (19.5)	70.6 (16.6)	<0.001	66.3 (16.5)	64.7 (17.5)	0.353	64.9 (17.3)	64.5 (17.7)	0.782
Gender, male, n (%)	334 (63.5)	266 (62.3)	0.753	116 (58.9)	122 (61.9)	0.607	117.5 (61.9)	120.1 (62.3)	0.934
BMI, kg/m^2	26.8 (6.3)	27.1 (7.5)	0.483	26.5 (6.1)	27.1 (7.3)	0.409	26.9 (6.3)	26.9 (7.1)	0.969
Number of fracture, (%)			0.171			0.972			0.753
1	106 (20.2)	70 (16.4)		35 (17.8)	33 (16.8)		33.6 (17.7)	28.5 (14.8)
2–3	78 (14.8)	57 (13.3)		26 (13.2)	24 (12.2)		25.8 (13.6)	27.5 (14.3)
4 or more	140 (26.6)	107 (25.1)		51 (25.9)	51 (25.9)		53.0 (27.9)	51.2 (26.5)
Multiple	202 (38.4)	193 (45.2)		85 (43.1)	89 (45.2)		77.4 (40.8)	85.7 (44.4)
Interventions, n (%)
MV	221 (42.0)	235 (55.0)	<0.001	95 (48.2)	95 (48.2)	1.000	93.1 (49.0)	93.9 (48.7)	0.934
CRRT	3 (0.6)	23 (5.4)	<0.001	2 (1.0)	1 (0.5)	1.000	2.2 (1.1)	1.8 (0.9)	0.804
Vasopressors	99 (18.8)	191 (44.7)	<0.001	67 (34.0)	67 (34.0)	1.000	61.3 (32.3)	62.3 (32.3)	0.999
Severity score, points
SOFA	3.6 (1.0)	6.2 (2.1)	<0.001	4.7 (1.3)	4.8 (1.6)	0.739	4.7 (2.3)	4.7 (2.5)	0.989
OASIS	29.9 (8.0)	35.7 (9.0)	<0.001	33.6 (7.6)	33.1 (8.0)	0.558	33.3 (7.9)	33.1 (8.0)	0.792
APSIII	38.1 (18.7)	55.8 (24.1)	<0.001	47.1 (21.9)	47.2 (19.8)	0.948	47.0 (22.1)	46.9 (19.5)	0.973
SAPSII	25.8 (11.2)	40.1 (13.6)	<0.001	34.1 (10.0)	33.7 (11.8)	0.690	33.3 (10.6)	33.1 (10.6)	0.809
Comorbidities, n (%)
Hypertension	176 (33.5)	174 (40.7)	0.024	87 (44.2)	88 (44.7)	1.000	84.5 (44.5)	86.0 (44.6)	0.995
Diabetes	65 (12.4)	93 (21.8)	<0.001	34 (17.3)	39 (19.8)	0.604	32.1 (16.9)	32.4 (16.8)	0.975
CKD	8 (1.5)	63 (14.8)	<0.001	6 (2.0)	11 (5.6)	0.321	5.9 (3.1)	7.4 (3.9)	0.647
Myocardial infarct	20 (3.8)	58 (13.6)	<0.001	16 (8.1)	17 (8.6)	1.000	15.5 (8.2)	15.8 (8.2)	0.997
CHF	31 (5.9)	109 (25.5)	<0.001	26 (13.2)	26 (13.2)	1.000	24.9 (13.1)	24.5 (12.7)	0.883
COPD	93 (17.7)	74 (17.3)	0.955	34 (17.3)	38 (19.3)	0.696	34.3 (18.0)	35.7 (18.5)	0.899
Liver disease	34 (6.5)	56 (13.1)	0.001	20 (10.2)	18 (9.1)	0.864	18.8 (9.9)	18.8 (9.7)	0.951
Malignancy	22 (4.2)	20 (4.7)	0.829	7 (3.6)	9 (4.6)	0.799	8.2 (4.3)	8.2 (4.3)	0.988
Charlson index	2.7 (1.3)	5.2 (2.7)	<0.001	4.2 (1.3)	4.1 (2.4)	0.761	4.1 (1.3)	4.0 (1.3)	0.962
Vital signs
MAP, mmHg	90.7 (17.0)	86.1 (20.2)	<0.001	88.7 (17.0)	88.9 (21.8)	0.910	89.2 (17.4)	88.9 (19.2)	0.835
Heart rate, bpm	91.7 (18.6)	89.4 (19.8)	0.070	89.7 (18.5)	89.3 (18.5)	0.834	89.6 (18.6)	89.3 (19.2)	0.835
RR, bpm	19.6 (5.8)	20.0 (5.5)	0.346	20.4 (6.8)	19.9 (5.1)	0.400	20.1 (6.3)	20.0 (5.2)	0.794
SpO2, %	97.3 (3.4)	96.5 (4.3)	0.001	96.8 (4.1)	96.7 (4.3)	0.783	96.9 (4.1)	96.9 (3.9)	0.963
Laboratory results
WBC, × 10^9/L	12.2 (5.3)	13.4 (5.6)	0.019	12.2 (5.6)	12.3 (5.4)	0.865	12.4 (5.7)	12.5 (5.8)	0.986
HGB, g/dL	11.8 (2.0)	10.9 (2.1)	<0.001	11.3 (2.0)	11.3 (2.0)	0.769	11.4 (2.0)	11.3 (2.1)	0.856
PLT, × 10^9/L	202.9 (77.3)	190.0 (66.1)	0.015	193.2 (78.3)	194.8 (78.8)	0.837	195.2 (78.2)	194.9 (83.0)	0.966
Glucose, mg/dl	136.3 (49.6)	162.0 (76.2)	<0.001	148.8 (65.1)	151.4 (62.9)	0.684	150.4 (64.9)	151.4 (63.6)	0.863
Bilirubin, mmol/L	1.1 (0.5)	1.4 (0.7)	0.032	1.2 (0.4)	1.3 (0.3)	0.687	1.2 (0.4)	1.2 (0.3)	0.855
Anion gap, mEq/L	14.7 (3.6)	15.2 (4.1)	0.030	14.8 (3.7)	14.7 (3.6)	0.890	14.7 (3.7)	14.7 (3.6)	0.881
Bicarbonate, mEq/L	22.9 (3.9)	22.5 (4.2)	0.192	22.8 (4.3)	22.7 (3.8)	0.802	22.9 (4.2)	22.8 (4.0)	0.942
Chloride, mmol/L	104.2 (6.0)	104.6 (6.4)	0.421	104.6 (6.5)	104.5 (6.1)	0.861	104.6 (6.3)	104.6 (6.2)	0.929
Creatinine, mg/dL	0.8 (0.3)	1.3 (0.7)	<0.001	0.9 (0.4)	1.0 (0.4)	0.069	1.0 (0.4)	1.0 (0.3)	0.636
Potassium, mmol/L	4.1 (0.7)	4.4 (0.8)	<0.001	4.3 (0.8)	4.3 (0.8)	0.652	4.3 (0.8)	4.3 (0.7)	0.905
Sodium, mmol/L	138.6 (4.6)	139.0 (5.0)	0.229	138.9 (5.0)	138.7 (4.5)	0.656	138.8 (4.9)	138.9 (4.6)	0.996
Clinical outcomes
AKI stages, n (%)			<0.001			<0.001			<0.001
No AKI	370 (80.3)	124 (29.0)		121 (61.4)	71 (36.0)		119.4 (62.9)	70.9 (36.7)
Stage I	40 (7.6)	64 (15.0)		22 (11.2)	31 (15.7)		19.0 (10.0)	32.7 (17.0)
Stage II	93 (17.7)	173 (40.5)		41 (20.8)	81 (41.1)		39.1 (20.6)	76.7 (39.8)
Stage III	23 (4.4)	66 (15.5)		13 (6.6)	14 (7.1)		12.2 (6.4)	12.6 (6.5)

Notes: For all continuous covariates, the mean values and standard deviations are reported.

Abbreviations: BAR, blood urea nitrogen to serum albumin ratio, BMI, body mass index, MV, mechanical ventilation, CRRT, continuous renal replacement therapy, SOFA, sequential organ failure assessment, OASIS, Oxford Acute Severity of Illness Score, APSIII, Acute Physiology Score III, SAPSII, Simplified Acute Physiology Score II, CKD, chronic kidney disease, CHF, congestive heart failure, COPD, chronic obstructive pulmonary disease, MAP, mean arterial pressure, RR, respiratory rate, WBC, white blood cell, HGB, hemoglobin, PLT, platelet, AKI, acute kidney injury.

Table 2 Univariate and Multivariate Logistic Analysis of BAR for the Development of AKI

	Original Cohort		Matched Cohort		Weighted Cohort
	OR (95% CI)	P value	OR (95% CI)	P value	OR (95% CI)	P value
Unadjusted	5.80 (4.39–7.69)	<0.001	3.01 (2.01–4.56)	<0.001	2.92 (2.03–4.21)	<0.001
Model 1	5.98 (4.34–8.32)	<0.001	3.18 (2.08–4.92)	<0.001	3.18 (2.17–4.65)	<0.001
Model 2	5.45 (3.91–7.65)	<0.001	3.22 (2.09–5.02)	<0.001	3.26 (2.22–4.78)	<0.001
Model 3	3.88 (2.66–5.71)	<0.001	4.20 (2.59–6.95)	<0.001	4.07 (2.71–6.10)	<0.001
Model 4	3.85 (2.58–5.79)	<0.001	4.47 (2.71–7.53)	<0.001	4.28 (2.80–6.53)	<0.001

Notes: Model 1 adjusted for age, gender, body mass index and number of fracture. Model 2 adjusted for model 1 plus comorbidities. Model 3 adjusted for Model 2 plus score systerm, interventions and Charlson index. Model 4 adjusted for model 3 plus vital signs and laboratory results.

Abbreviations: AKI, acute kidney injury, OR, odds ratio, 95% CI, 95% confidence index.

Figure 2 Decision curve analysis of BAR for incident AKI in rib fracture patients to detect its clinical usefulness in the original cohort (A) and in the matched cohort (B).

Table 3 NRI and IDI Analyses for Risk Reclassification of AKI in the Original Cohort and in the Matched Cohort

Outcome			AUC				IDI		NRI^a
	Sensibility (%)	Specificity (%)	Biomarker	Biomarker+ Clinical Model	Clinical Model^b	P value^c	Value (95% CI)	P value	Value (95% CI)	P value
Original cohort
BAR	73.0	71.7	0.757	0.854	0.835	<0.001	0.066 (0.050–0.081)	<0.001	0.134 (0.078–0.191)	<0.001
APSIII	66.0	74.9	0.705	0.839		<0.001	0.009 (0.003–0.016)	0.045	0.034 (−0.003–0.071)	0.075
BAR+APSIII	71.7	75.3	0.812	0.855		<0.001	0.075 (0.058–0.092)	<0.001	0.172 (0.111–0.233)	<0.001
Matched cohort
BAR	71.3	60.2	0.711	0.837	0.789	<0.001	0.105 (0.071–0.132)	<0.001	0.172 (0.071–0.270)	0.0008
APSIII	69.9	61.5	0.687	0.793		0.0004	0.013 (0.002–0.023)	0.018	0.112 (0.052–0.173)	0.0003
BAR+APSIII	85.4	52.3	0.767	0.841		<0.001	0.117 (0.085–0.149)	<0.001	0.256 (0.150–0.362)	<0.001

Notes: ^aThe NRI is calculated through two-way category by using the event rate of acute kidney injury. ^bThe clinical model for predicting AKI are composed of age, gender, BMI, comorbidities, interventions, vital signs, laboratory results and score system except APSIII score. ^cBiomarker+clinical model versus clinical model.

Abbreviations: AUC, area under the receiver-operating characteristic curve; IDI, integrated discrimination improvement; NRI, net reclassification index; BAR, blood urea nitrogen to serum albumin ratio, APSIII, Acute Physiology Score III.

Figure 3 Subgroup analysis for odds ratio of rib fracture patients with BAR ≥ 5.26 versus BAR < 5.26 in different groups in the original cohort (A) and in the matched cohort (B).