The Incidence of Acute Kidney Injury and Associated Hospital Mortality

Abstract

Background: Studies from multiple countries have shown that acute kidney injury (AKI) in hospitalized patients is associated with mortality and morbidity. There are no reliable data at present on the incidence and mortality of AKI episodes among hospitalized patients in Germany. The utility of administrative codings of AKI for the identification of AKI episodes is also unclear.

Methods: In an exploratory approach, we retrospectively analyzed all episodes of AKI over a period of 3.5 years (2014-2017) on the basis of routinely obtained serum creatinine measurements in 103 161 patients whose creatinine had been measured at least twice and who had been in the hospital for at least two days. We used the "Kidney Disease: Improving Global Outcomes" (KDIGO) criteria for AKI. In parallel, we assessed the administrative coding of discharge diagnoses of the same patients with codes from the International Classification of Diseases (ICD-10-GM).

Results: Among 185 760 hospitalizations, stage 1 AKI occurred in 25 417 cases (13.7%), stage 2 in 8503 cases (4.6%), and stage 3 in 5881 cases (3.1%). AKI cases were associated with length of hospital stay, renal morbidity, and overall mortality, and this association was stage-dependent. The in-hospital mortality was 5.1% for patients with stage 1 AKI, 13.7% for patients with stage 2 AKI, and 24.8% for patients with stage 3 AKI. An administrative coding for acute kidney injury (N17) was present in only 28.8% (11 481) of the AKI cases that were identified by creatinine criteria. Like the AKI cases overall, those that were identified by creatinine criteria but were not coded as AKI had significantly higher mortality, and this association was stage-dependent.

Conclusion: AKI episodes are common among hospitalized patients and are associated with considerable morbidity and mortality, yet they are inadequately documented and probably often escape the attention of the treating physicians.

Figure 1

Possible scenarios of AKI episodes: a) Creatinine was already elevated at the time of inpatient admission, with no knowledge of previous creatinine levels. In the further course, renal function recovers and creatinine drops to the assumed baseline level. b) Creatinine is already elevated at the time of inpatient admission. Baseline creatinine is known from previous hospital stays. c) Creatinine is not elevated at the time of admission, but rises over the course of the inpatient stay. AKI, acute kidney injury

Figure 2

Stage-dependent long-term survival following creatinine-based acute kidney injury (stages 1–3 according to KDIGO) a) Stage-dependent Kaplan-Meier survival curves for the total population. b) Stage-dependent Kaplan-Meier survival curves for the subgroup of patients whose administrative coding did not indicate acute kidney injury (N17) (N = 97 126 patients). In each case, the number at risk for the following time interval is shown. AKI, acute kidney injury; KDIGO, Kidney Disease: Improving Global Outcomes

eFigure

Study flow chart: Each case represents a hospital stay; thus, a proportion of patients experienced several cases during the observation period.