Preoperative serum cystatin C combined with dipstick proteinuria predicts acute kidney injury after cardiac surgery

Figures & data

Table 1 Basic patient demographic characteristics, classified with cystatin C or proteinuria in 616 patients undergoing cardiac surgery.

		Cystatin C Quartiles					Proteinuria on dipstick
	All	Quartile 1 (0.38–0.83 mg/L)	Quartile 2 (0.83–1.00 mg/L)	Quartile 3 (1.00–1.21 mg/L)	Quartile 4 (1.21–2.95 mg/L)	p Value	None	Mild	Heavy	p Value
No. of patients	616	154	154	158	150		367	190	59
Patient characteristics
Age, mean ± SD, years	60.7 ± 13.2	53.7 ± 13.4	59.6 ± 12.8	61.6 ± 13.5	65.2 ± 11.2	<0.001	61.4 ± 12.3	59.2 ± 13.3	61.4 ± 15.8	0.179
Male, n	393 (62.4%)	89 (57.8%)	98 (63.6%)	102 (64.5%)	104 (69.3%)	0.218	235 (64%)	124 (65.3%)	34 (57.6%)	0.556
Comorbidities
Hypertension, n	196 (31.8%)	39 (25.3%)	48 (31.2%)	52 (32.9%)	57 (38.0%)	0.124	107 (29.2%)	69 (36.3%)	20 (33.9%)	0.218
DM, n	112 (18.2%)	27 (17.5%)	21 (13.6%)	32 (20.3%)	32 (21.3%)	0.303	58 (15.8%)	35 (18.4%)	19 (32.2%)	0.010
PAD, n	11 (1.8%)	1 (0.6%)	3 (1.9%)	3 (1.9%)	4 (2.7%)	0.608	5 (1.4%)	4 (2.1%)	2 (3.4%)	0.764
CVA, n	22 (3.6%)	4 (2.6%)	2 (1.3%)	7 (4.4%)	9 (6.0%)	0.130	12 (3.3%)	6 (3.2%)	4 (6.8%)	0.387
CHF, n	119 (19.3%)	12 (7.8%)	23 (14.9%)	37 (23.4%)	47 (31.3%)	<0.001	48 (13.1%)	52 (27.4%)	19 (32.2%)	<0.001
COPD, n	10 (1.6%)	2 (1.3%)	3 (1.9%)	1 (0.6%)	4 (2.7%)	0.447	4 (1.1%)	5 (2.6%)	1 (1.7%)	0.321
Hyperuricemia, n	157 (25.5%)	22 (14.3%)	32 (20.8%)	44 (27.8%)	59 (39.3%)	<0.001	89 (24.3%)	45 (23.7%)	23 (38.9%)	0.043
recent MI, n	55 (8.9%)	6 (3.9%)	9 (5.8%)	17 (10.8%)	23 (15.3%)	0.002	28 (7.6%)	22 (11.6%)	5 (8.5%)	0.318
LVEF < 45%, n	56 (9.1%)	10 (6.5%)	14 (9.1%)	14 (8.9%)	18 (12.0%)	0.423	22 (6.0%)	27 (14.2%)	7 (11.9%)	0.005
Surgical characteristics
Prior cardiac surgery, n	17 (2.8%)	7 (3.9%)	2 (1.9%)	4 (2.5%)	4 (2.7%)	0.378	10 (2.7%)	6 (3.2%)	1 (1.7%)	0.819
Non elective surgery, n	4 (0.6%)	0 (0%)	1 (0.6%)	1 (0.6%)	2 (1.3%)	0.476	2 (0.5%)	2 (1.1%)	0 (0%)	0.739
Preoperative use of statins, n	230 (37.3%)	51 (33.1%)	66 (42.9%)	59 (37.3%)	54 (36.0%)	0.351	148 (40.3%)	68 (35.8%)	14 (23.7%)	0.046
Surgery types
CABG, n	239 (37.9%)	57 (37.0%)	69 (43.6%)	57 (36.1%)	56 (37.3%)	0.369	149 (40.6%)	69 (36.3%)	21 (35.6%)	0.542
Valve, n	292 (46.3%)	82 (53.2%)	71 (46.1%)	81 (51.3%)	58 (38.7%)	0.051	174 (47.4%)	94 (49.5%)	24 (40.7%)	0.497
CABG + valve, n	52 (8.3%)	6 (3.9%)	7 (4.5%)	12 (7.6%)	27 (18.0%)	<0.001	28 (7.6%)	16 (8.4%)	8 (13.6%)	0.325
Aortic, n	17 (2.7%)	3 (1.9%)	3 (1.9%)	5 (3.2%)	6 (4%)	0.666	7 (1.9%)	7 (3.7%)	3 (5.1%)	0.248
CHD, n	5 (0.8%)	2 (1.3%)	1 (0.6%)	1 (0.6%)	1 (0.7%)	0.939	2 (0.5%)	2 (1.1%)	1 (1.7%)	0.546
Others, n	11 (1.7%)	4 (2.6%)	3 (1.9%)	2 (1.3%)	2 (1.3%)	0.823	9 (2.5%)	3 (1.6%)	0 (0%)	0.679
Preoperative laboratory data
SCr, mean ± SD, μmol/L	75.8 ± 26.4	60.8 ± 17.3	67.3 ± 15.1	73.4 ± 17.6	101.3 ± 41.2	<0.001	73.2 ± 23.5	75.3 ± 23.5	95.9 ± 53.4	0.000
eGFR, mean ± SD, mL/min	96.3 ± 29.0	118.2 ± 28.9	105.5 ± 25.7	95.4 ± 24.7	71.6 ± 25.0	<0.001	97.7 ± 27.7	97.3 ± 28.5	80.6 ± 32.0	0.000
Hemoglobin (g/dL)	12.8 ± 1.8	13.1 ± 1.6	12.8 ± 1.8	12.9 ± 2.0	12.4 ± 2.0	0.061	12.9 ± 1.7	12.7 ± 1.7	12.5 ± 2.2	0.346
BNP, ng/L	267.6 ± 340.7	162.3 ± 231.3	200.8 ± 212.3	295.3 ± 385.9	396.0 ± 444.2	<0.001	237.7 ± 320.3	294.6 ± 350.9	418.9 ± 427.1	0.019
Preoperative biomarker
Heavy proteinuria, n	59 (9.6%)	11 (7.1%)	13 (8.4%)	11 (7.0%)	24 (16%)	0.021	–	–	–	–
Serum cystatin C (mg/L)	1.05 ± 0.33	0.70 ± 0.09	0.92 ± 0.04	1.10 ± 0.06	1.48 ± 0.32	<0.001	1.01 ± 0.28	1.03 ± 0.29	1.38 ± 0.55	0.000

Notes: Data are expressed as mean ± SD or number (percentage).

PAD = peripheral arterial disease; CVA = cerebral vascular accident; CHF = congestive heart failure; COPD = chronic obstructive pulmonary disease; MI = myocardial infarction; LVEF = left ventricular ejection fraction; CABG = coronary artery bypass grafting; CHD = congenital heart disease; SCr = serum creatinine; eGFR = estimated glomerular filtration rate; and BNP = brain natriuretic peptide.

Table 2 Percentage of patients with proteinuria in groups stratified by quartiles of cystatin C.

Cystatin C Quartiles	Normal	Mild proteinuria	Heavy proteinuria	Subtotal
Quartile 1	96 (62.3%)	47 (30.5%)	11 (7.1%)	154
Quartile 2	99 (64.3%)	42 (27.3%)	13 (8.4%)	154
Quartile 3	93 (58.9%)	54 (33.5%)	11 (6.9%)	158
Quartile 4	79 (52.7%)	47 (32.0%)	24 (16.0%)	150

Figure 1. Unadjusted risk for postoperative AKI, persistent AKI, severe AKI, dialysis and hospital mortality in patients with quartiles of cystatin C (A) and different severities of proteinuria (B). Comparison on patients with quartiles 1 of cystatin C or normal proteinuria. *p < 0.05 and #p < 0.001.

Table 3 Adverse outcomes in 616 patients with various quartiles of cystatin C and degree of proteinuria.

		Cystatin C quartiles					Proteinuria on dipstick
	All	Quartile 1 (0.38–0.83 mg/L)	Quartile 2 (0.83–1.00 mg/L)	Quartile 3 (1.00–1.21 mg/L)	Quartile 4 (1.21–2.95 mg/L)	p Value	None	Mild	Heavy	p Value
No. of patients	616	154	154	158	150		367	190	59
AKI	179 (28.4%)	20 (13.0%)	36 (23.4%)	48 (30.4%)	75 (50.0%)	<0.001	99 (27.0%)	54 (28.4%)	26 (44.1%)	0.027
Persistent AKI	93 (15.1%)	10 (6.5%)	22 (14.3%)	18 (11.4%)	43 (28.7%)	<0.001	49 (13.4%)	27 (14.2%)	17 (28.8%)	0.008
Severe AKI	69 (11.2%)	4 (2.6%)	18 (11.7%)	19 (12.0%)	28 (18.7%)	<0.001	33 (9.0%)	20 (10.5%)	16 (27.1%)	<0.001
Dialysis	6 (1.0%)	0 (0.0%)	0 (0.0%)	1 (0.6%)	5 (3.3%)	0.005	1 (0.3%)	2 (1.1%)	3 (5.1%)	0.008
Length of ICU stay (days)	3 (2.4)	3 (2.3)	3 (2.4)	3 (2.4)	3 (3.4)	<0.001	3 (2.4)	3 (2.4)	4 (3.5)	0.093
Duration of mechanical   ventilation (hours)	17 (12.20)	15 (10.19)	17 (11.20)	17 (12.20)	18 (13.24)	0.073	17 (11.20)	17 (12.20)	19 (15.28)	0.035
Mortality	8 (1.3%)	0 (0.0%)	2 (1.3%)	3 (1.9%)	4 (2.7%)	0.196	3 (0.8%)	2 (1.1%)	3 (5.1%)	0.048

Table 4 Multivariate logistic regression analysis of risk factors for the development of AKI in 616 cardiac surgery patients.

Covariate	OR	95% CI	p Value
Age (years)	1.04	1.01–1.06	0.002
Hypertension	1.88	1.13–3.12	0.015
Combined surgery	3.47	1.35–8.89	0.010
Heavy proteinuria	3.14	1.26–7.77	0.014
Cystatin C quartile
Quartile 1	1
Quartile 2	1.60	0.72–3.60	0.276
Quartile 3	1.87	0.85–4.14	0.119
Quartile 4	3.10	1.37–7.02	0.006

Figure 2. ROC analysis curve showing the predictive value of cystatin C combined with proteinuria, eGFR and Scr.