Study population
In consecutive 866 adult patients (age ≥ 18 years) who underwent screening, we excluded patients with end stage renal disease (ESRD) (n = 38), anuria (n = 53), and AKI stage 2 and 3 on admission (n = 102), incomplete data (n = 96). Therefore, the study included 577 patients. 96 patients developed to severe AKI (16.6%) within 7 days in ICU. The flowchart of this study and the number of patients is presented in Fig. 1.
Patient characteristics
Patient characteristics are listed in Table 1. Severe AKI group enrolled 96 (16.6%) patients and no severe AKI group enrolled 481 (83.4%) patients. The mean ages of severe AKI group and no severe AKI group were respectively 73 (58–81) and 67 (51–77) (P = 0.004). The patients of severe AKI group were older. The proportion of males in severe AKI group and no severe AKI group was respectively 66.7% and 62.6% (P = 0.448). Compared with patients of no severe AKI group, patients of severe AKI group were significantly older, had a higher body mass index and had more CKD, sepsis and hypotension (Map < 70 mmHg). ICU patients in the severe AKI group also had a higher SCr level, lactate level, NephroCheck value and PCT level on admission.
Table 1
Baseline characteristics and outcomes of the study population by presence or absence of severe AKI within 7 days
Variable | Severe AKI | No Severe AKI | P Value |
N | 96(16.6) | 481(83.4) | |
Age (years) | 73(58–81) | 67(51–77) | 0.004 |
Male | 64(66.7) | 301(62.6) | 0.448 |
BMI (kg/m2) | 26.18(23.03–29.41) | 24.8(22.86–27.68) | 0.037 |
SAPSII | 44(34–52) | 38(27–50) | 0.153 |
Chronic risk factors | | | |
Age > 65 years | 66(68.8) | 256(53.2) | 0.005 |
BMI > 30 kg/m2 | 21(21.9) | 61(12.7) | 0.039 |
Hypertension | 48(50) | 212(44.1) | 0.49 |
DM | 21(21.9) | 66(13.7) | 0.138 |
CKD | 20(20.8) | 39(8.1) | < 0.001 |
Lung diseases | 8(8.3) | 43(8.9) | 0.848 |
CVD | 10(10.4) | 58(12.1) | 0.649 |
Acute risk factors | | | |
Sepsis | 20(20.8) | 41(8.5) | < 0.001 |
Surgery | 18(18.8) | 67(13.9) | 0.224 |
Vasopressor | 46(47.9) | 179(37.2) | 0.05 |
Mechanical ventilation | 71(74) | 329(68.4) | 0.281 |
Map < 70 mmHg | 40(41.7) | 109(22.7) | < 0.001 |
Biochemical indicators | | | |
Serum creatinine, admission(mg/dl) | 1.08 (0.75–1.45) | 0.83(0.65–1.08) | < 0.001 |
Serum lactate, admission (mmol/l) | 2.1(1.4–3.8) | 1.6(1.2–2.6) | 0.001 |
NephroCheck value, admission((ng/ml)2/1000) | 0.66(0.23–2.49) | 0.29(0.08–0.86) | < 0.001 |
PCT, admission(ug/l) | 1.19(0.28–6.81) | 0.26(0.10–1.45) | < 0.001 |
Nephrocheck (+) | 69(71.9) | 233(48.4) | < 0.001 |
PCT (+) | 54(56.3) | 115(23.9) | < 0.001 |
Outcomes | | | |
CRRT | 11(11.5) | 6(1.2) | < 0.001 |
Death | 32(33.3) | 63(13.1) | < 0.001 |
LOS(d) | 5(2–8) | 3(2–7) | 0.034 |
Data are expressed as n (%) or median (interquartile range). |
Severe AKI within 7 days is associated with poor outcomes in ICU patients
Table 1 shows 11.5% of patients in severe AKI group and 1.2% of patients in no severe AKI group required CRRT (P < 0.001). Severe AKI was also associated with ICU mortality. The mortality incidence was 33.3% in severe AKI group and 13.1% in no severe AKI group respectively (P < 0.001). Severe AKI also increased LOS in ICU. LOS of severe AKI group and no severe AKI group were 5 (2–8) and 3 (2–7) respectively (P = 0.034).
Univariate variables associated with severe AKI within 7 days
Table 2 provides a list of significant univariate variables associated with severe AKI within 7 days. The presence of hypertension, CVD, lung disease, high-risk surgery, mechanical ventilation and SAPSII cannot predict the development of AKI in our cohort. Among the chronic risk factors, age > 65 years, BMI > 30 kg/m2, DM and CKD could predict severe AKI, the relative risk was 1.934 (95% CI(1.212–3.085,) P = 0.006), 1.887 (95% CI(1.085–3.282), P = 0.025), 1.748 (95% CI (1.009–3.027), P = 0.046), 2.982 (95% CI (1.651–5.388), P < 0.001). Among the acute risk factors, sepsis and MAP < 70 mmHg could predict severe AKI, with a relative risk of 2.824 (95% CI (1.570–5.081), P = 0.001) and 2.431 (95% CI (1.537–3.845), P < 0.001). Among biochemical indicators, elevated SCr level was associated with a relative risk of 1.697 of developing severe AKI (95% CI (1.263–2.28), P < 0.001). For increase in serum lactate concentration, there was a 11.5% increased relative risk of developing severe AKI (OR = 1.115, 95% CI (1.036–1.199), P = 0.003). In addition, NephroCheck (+) predicts the development of severe AKI with a relative risk of 2.72 (95% CI (1.684–4.394), P < 0.001). PCT (+) predicts the development of severe AKI with a relative risk of 4.883 (95% CI (2.625–9.084), P < 0.001).
Table 2
Logistic regression analysis for predictor of severe AKI within 7 days
Variable | Univariate | Multivariate |
Chronic risk factors | | |
Age > 65 years | 1.934 (1.212–3.085) | 1.961(1.153–3.336) |
BMI > 30 kg/m2 | 1.887 (1.085–3.282) | NS |
DM | 1.748 (1.009–3.027) | NS |
CKD | 2.982 (1.651–5.388) | 2.573(1.319–5.018) |
Acute risk factors | | |
Sepsis | 2.824 (1.570–5.081) | NS |
MAP < 70 mmHg | 2.431 (1.537–3.845) | NS |
Biochemical indicators | | |
Serum creatinine, admission(mg/dl) | 1.697 (1.263–2.281) | NS |
Serum lactate, admission (mmol/l) | 1.115 (1.036–1.199) | NS |
Nephrocheck (+) | 2.720 (1.684–4.394) | 2.139(1.260–3.630) |
PCT (+) | 4.883 (2.625–9.084) | 3.223(1.643–6.321) |
Data are expressed as odds ratio (95% CI). NS: Nonsignificant predictors. |
Independent predictors of severe AKI within 7 days
Multivariate logistic regression was performed with univariate variables related to severe AKI within seven days. Following the variable selection, 4 independent predictors, including age > 65 years (OR = 1.961, 95% CI (1.153–3.336), P = 0.013), CKD (OR = 2.573, 95% CI (1.319–5.018), P = 0.006), NephroCheck (+) on admission (OR = 2.139, 95% CI (1.260–3.630), P = 0.005) and PCT (+) on admission (OR = 3.223, 95% CI (1.643–6.321), P = 0.001), predicted the development of severe AKI (Table 2).
NephroCheck level on admission was associated with incidence of severe AKI within 7 days and its poor outcomes
For the 577 patients, 275 (47.7%) were NephroCheck ≤ 0.3 (ng/ml)2/1000, 220 (38.1%) were NephroCheck (0.3-2) (ng/ml)2/1000 and 82 (14.2%) were NephroCheck ≥ 2(ng/ml)2/1000. Severe AKI incidence within seven days, CRRT initiation and ICU mortality were highest in NephroCheck ≥ 2(ng/ml)2/1000 group. The incidence of severe AKI within seven days increased from 9.8% in NephroCheck ≤ 0.3 (ng/ml)2/1000 patients to 19.1% in NephroCheck (0.3-2) (ng/ml)2/1000 patients and 32.9% in NephroCheck ≥ 2(ng/ml)2/1000 patients (compared in 3 groups, P < 0.001). The treatment of CRRT increased from 1.1% in NephroCheck ≤ 0.3 (ng/ml)2/1000 patients to 2.7% in NephroCheck (0.3-2) (ng/ml)2/1000 patients and 9.6% in NephroCheck ≥ 2(ng/ml)2/1000 patients (compared in 3 groups, P < 0.001). ICU mortality increased from 13.5% in NC (-) patients to 16.8% in NephroCheck (0.3-2) (ng/ml)2/1000 patients and 25.6% in NephroCheck ≥ 2(ng/ml)2/1000 patients (compared with 3 groups, P = 0.033) (Fig. 2).
Incorporation of risk factors augments the predictive performance of the NephroCheck
Compared to NephroCheck (+) only (AUC = 0.66, 95% CI:0.60–0.72), the combination of NephroCheck (+) and risk factors (age > 65years, CKD and PCT positive) (AUC = 0.75, 95% CI:0.70–0.81) led to a significant increase in the area under ROC curve for severe AKI prediction within 7 days (Fig. 3).