Association between serum uric acid levels and clinical outcomes in patients with acute kidney injury

Figures & data

Table 1. Baseline characteristics.

	Uric acid (mg/dl)
Variables	≤3.6 (n = 1174)	>3.6–5.1 (n = 1127)	>5.1–6.9 (n = 1189)	>6.9 (n = 1156)	p Value
Age	56.8 ± 17.8	56.9 ± 18.7	59.0 ± 17.7	59.5 ± 17.9	<0.001
Sex, male, n (%)	458 (39.0)	551 (48.9)	697 (58.6)	785 (67.9)	<0.001
BMI (kg/m^2)	23.6 ± 3.4	24.4 ± 3.7	24.8 ± 3.9	25.1 ± 4.3	<0.001
Emergency status, n (%)	630 (53.7)	554 (49.2)	498 (41.9)	474 (41.0)	<0.001
AKI stage, n (%)					<0.001
STAGE 1	1028 (87.6)	1011 (89.7)	1088 (91.5)	1042 (90.1)
STAGE 2	107 (9.1)	81 (7.2)	54 (4.5)	37 (3.2)
STAGE 3	39 (3.3)	35 (3.1)	47 (4.0)	77 (6.7)
Comorbidities, n (%)
CKD	46 (3.9)	143 (12.7)	230 (19.3)	390 (33.7)	<0.001
Diabetes	226 (19.3)	294 (26.1)	333 (28.0)	298 (25.8)	<0.001
Hypertension	347 (29.6)	507 (45.0)	711 (59.8)	751 (65.0)	<0.001
Heart disease	171 (14.6)	285 (25.3)	402 (33.8)	415 (35.9)	<0.001
Cancer	265 (22.6)	221 (19.6)	198 (16.7)	216 (18.7)	<0.001
Biochemical indices
Creatinine (μmol/L)^a	110 ± 147	186 ± 259	262 ± 320	425 ± 404	<0.001
Albumin (g/L)^a	37.3 ± 10.5	39.9 ± 10.4	41.2 ± 10.8	40.2 ± 10.9	<0.001
Cholesterol (g/L)^a	3.85 ± 1.41	4.19 ± 1.46	4.33 ± 1.44	4.18 ± 1.47	<0.001
Triglyceride (g/L)^a	1.11 ± 0.75	1.45 ± 1.10	1.69 ± 1.30	1.82 ± 1.34	<0.001
Hb (g/L)^a	114 ± 26	117 ± 26	119 ± 27	114 ± 30	<0.001
Medication
ACEI (%)	22 (1.9)	44 (3.9)	78 (6.6)	88 (7.6)	<0.001
ARB (%)	126 (10.7)	209 (18.5)	336 (28.3)	291 (25.2)	<0.001
BB (%)	452 (38.5)	505 (44.8)	659 (55.4)	666 (57.6)	<0.001
CCB (%)	227 (19.3)	304 (27.0)	451 (37.9)	474 (41.0)	<0.001
Furosemide (%)	192 (16.4)	232 (20.6)	290 (24.4)	424 (36.7)	<0.001
UA-lowering agent (%)	6 (0.5)	9 (0.8)	19 (1.6)	99 (8.6)	<0.001
eGFR, ml/min/1.73 m^2	75.8 ± 25.5	61.3 ± 29.0	48.1 ± 28.2	29.8 ± 24.3	<0.001
RRT requirement	82 (7.0)	126 (11.2)	173 (14.6)	308 (26.6)	<0.001

BMI: body mass index; AKI: acute kidney injury; CKD: chronic kidney disease; Hb: hemoglobin; ACEI: angiotensin-converting enzyme inhibitor; ARB: angiotensin II receptor blocker; BB: beta blocker; CCB: calcium channel blocker; UA: uric acid; eGFR: estimated glomerular filtration rate; RRT: renal replacement therapy.

^aThe first values during the first day after admission were recorded.

Figure 1. Flow chart of patient selection from the database.

Figure 2. Histogram of serum uric acid distribution.

Figure 3. Nonlinear relationship between SUA level and in-hospital mortality in AKI patients.

Figure 4. Kaplan–Meier survival curves of the study population.

Table 2. Odds ratio for in-hospital mortality according to SUA levels.

SUA (mg/dl)	Unadjusted			Model 1			Model 2
	OR	95% CI	p Value	OR	95% CI	p Value	OR	95% CI	p Value
≤3.6	reference			reference			reference
>3.6–5.1	1.37	0.94–2.01	0.098	1.31	0.89–1.92	0.172	1.24	0.82–1.88	0.306
>5.1–6.9	1.67	1.16–2.39	0.006	1.46	1.01–2.12	0.044	1.72	1.21–2.33	0.005
>6.9	3.64	2.62–5.05	<0.001	3.16	2.25–4.45	<0.001	2.75	1.78–4.26	<0.001

CI: confidence interval; OR: odds ratio; SUA: serum uric acid; AKI: acute kidney injury; CKD: chronic kidney disease; RRT: renal replacement therapy; eGFR: estimated glomerular filtration rate; BMI: body mass index.

Logistic regression: model 1 was adjusted for age, sex and BMI; model 2 was adjusted for age; sex; BMI; emergency status; AKI stage; presence of CKD, diabetes, hypertension, heart disease, or cancer; creatinine; albumin; cholesterol; triglyceride; Hb; eGFR and RRT requirement; and the use of angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, beta blockers, calcium channel blockers, furosemide and UA-lowering agents.

The mean variance inflation factor was 1.03 and 1.90 for Model 1 and Model 2, respectively.

Table 3. Odds ratio for nonrecovery of AKI according to SUA levels.

SUA (mg/dl)	Unadjusted			Model 1			Model 2
	OR	95% CI	p Value	OR	95% CI	p Value	OR	95% CI	p Value
≤3.6	reference			reference			reference
>3.6–5.1	1.03	0.88–1.22	0.671	1.09	0.92–1.29	0.340	1.14	0.86–1.52	0.167
>5.1–6.9	1.15	0.88–1.33	0.120	1.12	0.79–1.30	0.428	1.07	0.92–1.20	0.258
>6.9	1.51	1.12–2.01	0.012	1.59	1.07–1.98	<0.001	1.46	1.25–1.85	<0.001

CI: confidence interval; OR: odds ratio; SUA: serum uric acid; AKI: acute kidney injury; CKD: chronic kidney disease; RRT: renal replacement therapy; eGFR: estimated glomerular filtration rate; BMI: body mass index.

Logistic regression: model 1 was adjusted for age, sex and BMI; model 2 was adjusted for age; sex; BMI; emergency status; AKI stage; presence of CKD, diabetes, hypertension, heart disease, or cancer; creatinine; albumin; cholesterol; triglyceride; Hb; eGFR and RRT requirement; and the use of angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, beta blockers, calcium channel blockers, furosemide and UA-lowering agents.

The mean variance inflation factor was 1.03 and 1.90 for Model 1 and Model 2, respectively.

Table 4. Subgroup analyses of the association between SUA and in-hospital mortality.

Variables	N	OR (95% CI)	p value	p for interaction
Age				<0.001
<65	2771	1.11 (1.03–1.20)	0.007
≥65	1875	1.20 (1.12–1.28)	<0.001
Sex				<0.001
Male	2491	1.14 (1.07–1.21)	<0.001
Female	2155	1.27 (1.16–1.39)	<0.001
AKI stage				<0.001
Stage 1	4169	1.20 (1.14–1.27)	<0.001
Stage 2	279	1.52 (1.20–1.71)	<0.001
Stage 3	198	1.61 (1.31–1.97)	<0.001
UA-lowering agents				<0.001
No	4513	1.19 (1.13–1.25)	<0.001
Yes	133	1.16 (0.97–1.38)	0.109
Furosemide				<0.001
No	3508	1.23 (1.18–1.28)	<0.001
Yes	1138	1.18 (1.11–1.25)	<0.001
CKD				0.686
No	3837	1.16 (1.10–1.22)	<0.001
Yes	809	1.27 (1.11–1.46)	<0.001
Diabetes				<0.001
No	3495	1.17 (1.10–1.24)	<0.001
Yes	1151	1.31 (1.18–1.45)	<0.001

CI: confidence interval; OR: odds ratio; UA: uric acid; AKI: acute kidney injury; CKD: chronic kidney injury.

Figure 5. ROC curves for the prediction of mortality in patients with AKI.

Table 5. Performance of SUA levels for predicting in-hospital mortality in patients with AKI.

Variables	AUC (95% CI)	Sensitivity	Specificity	p Value
SUA	0.65 (0.62–0.68)	0.51	0.73	<0.001
Age	0.69 (0.66–0.72)	0.67	0.60	<0.001
SUA + Age	0.74 (0.71–0.77)	0.64	0.74	<0.001