Study population
In consecutive 866 adult patients (age ≥ 18 years) who underwent screening, 289 unsuitable patients were excluded. Therefore, the study included 577 patients and 96 of them developed to severe AKI (16.6%) within seven days in the ICU. The flowchart of this study and the number of patients are as presented in Fig.1. Admission diagnoses for these patients included surgery (14.7%), sepsis (10.6%), cardiovascular disease (11.8%), trauma (22.7%), respiratory diseases (8.8%), neurological diseases (21%) and other causes (10.4%).
Patient characteristics
Patient characteristics are listed in Table 1. Severe AKI group enrolled 96 (16.6%) patients and non-severe AKI group enrolled 481 (83.4%) patients. Compared with patients from the non-severe AKI group, patients of severe AKI group were significantly older, had a higher body mass index and more CKD, sepsis and hypotension (MAP<70mmHg). ICU patients in severe AKI group also had a higher SCr level, lactate level, NephroCheck value and PCT level on admission.
Severe AKI within seven 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 non-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 non-severe AKI group respectively (P <0.001). Severe AKI also increased LOS in ICU. LOS of severe AKI group and non-severe AKI group were 5 (2-8) and 3 (2-7), respectively (P = 0.034).
Univariate variables associated with severe AKI within seven days
Table 2 provides a list of significant univariate variables associated with severe AKI within seven days. The presence of hypertension, CVD, lung disease, high-risk surgery, mechanical ventilation and SAPSII cannot predict the development of AKI in our study. Among all chronic risk factors, age >65 years, BMI>30 kg/m2, DM and CKD could predict severe AKI, and 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), respectively. Among acute risk factors, sepsis and MAP<70mmHg 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). With an increase of serum lactate concentration, the risk of developing severe AKI (OR=1.115, 95% CI (1.036-1.199), P=0.003) would be increased by 11.5%. 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).
Independent predictors of severe AKI within seven days
Multivariate logistic regression was performed with univariate variables related to severe AKI within seven days. Following variable selection, four 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) were used to predict the development of severe AKI (Table 2).
NephroCheck level on admission was associated with incidence of severe AKI within seven days and its poor outcomes
For 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 the 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 with three 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 with three 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 three groups, P = 0.033) (Fig. 2).
Incorporation of risk factors augments the predictive performance of the NephroCheck
Compared with 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 prediction of severe AKI within seven days (Fig. 3).