Acute kidney injury (AKI) is associated with high morbidity and mortality, a high risk of development or progression of chronic kidney disease (CKD), and increased health care costs.1 A meta-analysis published in 2013, with 154 studies and more than 3.5 million patients included, reported an overall incidence of in-hospital AKI of 21.6%.2 This incidence can increase to 57% in intensive care units (ICUs).3 More recent studies have shown an increasing trend in the incidence of AKI. Pavkov et al. reported a 140% and 230% increase in the incidence of AKI in patients with and without diabetes, respectively, between 2000 and 2014.4.

The incidence of AKI is not well known in Spain. Using an automated system to detect a decrease in the glomerular filtration rate, Labrador Gómez et al. reported an AKI incidence of up to 45.5% in hospitalized patients.5 At the Andalusian level, no records that have analyzed the incidence of AKI exist.

The different definitions of AKI according to different guidelines, the absence of autonomous registries, and the lack of homogeneity in the characteristics of the patients included in the few available studies could be the cause of the scarcity and variability of data in this area. This leads to a lack of understanding of the true epidemiology of AKI, for both healthcare professionals and senior administrators in the hospital setting.

Some studies have focused on the prevention of AKI by identifying at-risk populations and applying interventions before the onset of AKI, and they have shown how early diagnosis and proper management promote better renal recovery and reduce the impact on morbidity and mortality.6–8 Unfortunately, when the quality of care received by hospitalized patients with AKI is examined retrospectively, numerous defects are revealed, such as late recognition, inadequate investigations, inefficient monitoring, delayed and inadequate management, and the absence of follow-up.8 Therefore, it is crucial to promote studies that give visibility to this condition and to appeal to and raise awareness among health organizations to achieve an improvement in the quality of care in this process, beginning with the analysis of the initial situation of each patient in each institution and providing adequate monitoring.

The objectives of our study were to determine the incidence of AKI among hospitalized adult patients from 2017 to 2021 in the Autonomous Community of Andalusia, analyze the impact of this diagnosis on mortality during hospital admission, assess the economic burden on the health system, identify those care units capable of implementing improvement strategies, and evaluate the impact that the care provided by the Nephrology Unit has on the outcomes of this population.

The incidence of AKI in our study was low (5.8%) compared with that in previous studies, where rates ranging from 7 to 21.6% were reported.2,8 This incidence is possibly underestimated in our analysis. The CMBD includes the clinical diagnoses issued by physicians in routine clinical practice. It is possible that certain AKI cases considered mild or in the context of a serious clinical scenario were omitted from the discharge report and therefore were not considered in this analysis. This underdiagnosis of AKI was also reported by Labrador Gómez et al.,5 who, using an automated system to detect a decrease in the glomerular filtration rate, reported an incidence of AKI of 45.5% compared with 7.7% of AKI diagnoses traditionally recorded in discharge reports.

In our study, there was a clear upward trend in the incidence of AKI over time. The causes that explain this increase are several-fold: aging of the general population with an increase in associated comorbidities and cardiovascular risk factors, a higher incidence of sepsis in patients in the ICU, a greater number of surgeries, and an increase in exposure to nephrotoxic drugs.9 We cannot rule out the growing awareness of the importance of AKI, which could explain the increase in AKI diagnoses among professionals.

It is worth noting the differences in incidence when cases are subdivided by care unit, with the diagnosis of AKI being more frequent in clinical units such as Nephrology, Internal Medicine, or Infectious Diseases and much less common in surgical units. We understand that there are four main reasons that explain this gap. First, the underreporting of AKI in surgical units, in which the reports do not usually include all the diagnoses presented by the patient during admission. Second, a possible lower awareness of the importance of kidney damage among these physicians could explain the underdiagnosis, especially for mild AKI with slight increases in serum creatinine levels. Third, the frequent, scheduled admissions that occur in surgical units assume an initially stable patient profile with a good clinical and analytical profile in most cases. Finally, the type of patient admitted to the Internal Medicine or Infectious Diseases Units has a higher comorbidity profile because of concomitant pathologies, advanced average age, and reasons for admission with a greater pathogenic likelihood for the development of AKI. In relation to the Nephrology Unit, a high incidence is expected given the baseline characteristics of the nephrological patient.

In our study, the diagnosis of AKI clearly led to a longer hospital stay (13.55 days vs. 7.69 days), higher economic cost (; 107,377.51 vs. ; 56,342.69) and higher mortality (23.03% vs. 4.03%) compared with patients admitted without AKI.

The available literature has already established that a diagnosis of AKI directly affects the average hospital length of stay and associated costs.8 In our study, there was again a difference depending on the unit studied, although the increase in average length of stay and costs in patients diagnosed with AKI is consistent. The most affected unit in our analysis was Orthopedic Surgery and Traumatology, where the detection of AKI quadrupled the average stay. However, the highest average length of stay, 25 days, was associated with Cardiovascular Surgery. This is probably because it is a unit with a greater number of unscheduled admissions and patients with significant hemodynamic complexity. In contrast, the detection of AKI in the departments of Internal Medicine, Medical Oncology, and Nephrology increased the average length of stay by only two days compared with patients without AKI. This could be due to several reasons. The main reason is the profile of the patient who presents with AKI in each unit compared with the rest of the patients. In surgical units, patients with AKI usually present with a series of complications associated with surgery or the postoperative period that, in many cases, involve surgical reinterventions, admission to the ICU, a multidisciplinary approach, etc. Another determining factor may be that the knowledge and experience in relation to the management of AKI that medical specialists usually have is greater than that of surgical specialists, resulting in earlier detection and treatment of AKI in the former.

Although AKI is a preventable, treatable, and potentially reversible clinical condition, it currently poses a large economic burden for the health system, especially if it is not managed properly.10,11 In our study, overall, the costs of hospital admissions without AKI were ; 56,342, whereas in those in which AKI was diagnosed, the costs were ; 107,377. In terms of this additional cost during hospitalization, it should be noted that patients with AKI have increased comorbidities in the medium–long term (increased risk of new episodes of AKI, progression to chronic kidney disease, greater number of rehospitalizations, and increased vascular comorbidity), which represents an additional increase in costs for the health system that is difficult to determine with the data available today.12,13

In terms of mortality, the difference between those episodes with an AKI diagnosis and those without an AKI diagnosis is evident in our data. Similarly, two previous meta-analyses reported a direct relationship between an AKI diagnosis and increased mortality.12,14 The most recent study, by See EJ et al.,12 included 82 studies that included 2,017,437 participants. These authors reported that people with AKI have a higher risk of death, with a hazard ratio of 1.80 (95% confidence interval (CI) 1.61–2.02) (13.19 versus 7.26 deaths per 100 person-years in the group without AKI).

Mortality rates were higher among patients admitted with a diagnosis of AKI in all care units. The incidence of AKI in the Medical Oncology Unit is notable. AKI is a frequent complication in oncological patients who have a compromised immune system and are subjected to nephrotoxic treatments. In turn, the clinical impact of AKI on these patients is important because it can hinder the management of neoplastic disease, limiting treatment options.15 Therefore, this considerable incidence rate with high associated mortality is not surprising, indicating that these units should consider implementing preventive strategies to avoid kidney damage and facilitate early diagnosis and intervention in these patients.

In the present study, the Oncology, Internal Medicine, and Digestive System Units had the highest incidence of AKI during hospitalization and the highest rates of associated mortality. These observations contrast with the data obtained in the Nephrology Unit, where despite presenting the highest incidence of AKI, most likely associated with clinical cases of AKI with greater complexity, the lowest mortality rates and an average length of stay less than that of the entire set of analyzed units were found.

These findings highlight the clinical and strategic value of the direct involvement of nephrologists in the care of patients with AKI. The experience and specific approach of nephrology in addressing this pathology allows not only improvement in clinical outcomes but also optimization of the efficiency of the system by reducing the duration of hospital admissions and, therefore, the associated costs.

From this perspective, it is especially relevant to develop an institutional strategy that favors the active participation of nephrologists in those units with poor results in the management of AKI. Priority measures include the shared etiological analysis of cases, the design of training programs for professionals from other specialties, the establishment of multidisciplinary collaboration protocols, and the systematic monitoring of the impact of the interventions implemented to identify opportunities for continuous improvement.

In light of the global data presented in this study, the urgent need for concrete measures becomes evident. The first fundamental step is to increase awareness among healthcare professionals, managers, and decision-makers in the healthcare sector about the profound negative impact of this condition, not only on the health of patients but also on the sustainability of the healthcare system. To achieve this, it is essential to have solid clinical information systems that allow accurate evaluation of the magnitude of the problem and generate quality scientific evidence. Without reliable and validated data, it is difficult to educate the individuals involved and promote effective strategies.

In this context, the role of the nephrologist is essential not only during hospitalization, as already mentioned, but also in the planning of adequate follow-up after discharge. Recent studies have shown the negative consequences in the medium and long term of having experienced an episode of AKI, which is associated with an increased risk of mortality, cardiovascular events, recurrence of AKI, and progression to CKD and even end-stage renal disease.12 This reality underscores the need for a specialized and continuous intervention that minimizes these risks and improves the outcome of patients.

This study has several limitations that should be considered when the results are interpreted. First, there is a risk of underreporting variables, often as a result of incomplete discharge reports where all diagnoses and procedures performed are not included. Second, the CMBD encodes the number of admissions regardless of the individual involved so that the same patient can appear repeatedly in the database. In addition, there is no standardized criterion for the diagnosis of AKI, nor has it been possible to establish its severity with the available data. Finally, the use of aggregated data leads to the loss of detailed information on the distribution of the data and the variability within each group, preventing fine adjustments or exploring specific subgroups.

Our study also presents several strengths that support the validity and reliability of the results obtained. The analysis was carried out on the entire admitted population, which gives the study a high degree of representativeness and allows a broad and accurate view of the variables analyzed to be obtained, reinforcing the applicability of the conclusions. In addition, the study presented a homogeneous coding that minimized the variability of the data collected each year, improving the reliability of the results. In addition, we consider that the analysis focused exclusively on patients with AKI admitted to the hospital ward provides a different approach than that usually found in the literature, where we find data on patients with AKI in the ICU. The care of the patient with AKI in the hospitalization wards falls on physicians of different specialties, some of whom have training deficiencies that can considerably affect the outcomes of these patients.

This study also provides added value by comparatively analyzing the impact of AKI in different care units, revealing significant differences in terms of both incidence and clinical and economic outcomes. To the best of our knowledge, this approach has not been previously explored in our environment, which reinforces the interest and originality of the work. This approach not only allows the identification of those units that require priority improvement interventions but also facilitates the design of specific measures adapted to the particularities of each type of unit, which would improve management and clinical results. Finally, the long study period allows us to capture the impact of the variables over the years, increasing the robustness of the results.

The overall incidence of hospital AKI reported in the CMBD in Andalusian hospitals is lower than that reported in the literature and is possibly underestimated by undercoding in clinical discharge reports. However, there is evidence of a progressive increase in the incidence of hospital AKI during the period of time studied, as well as a clear association between the diagnosis of AKI and increased average length of stay, increased economic cost, and increased hospital mortality.

Our analysis highlights the need to promote dialog between health professionals and policy-makers to increase awareness about AKI and its impact on public health. The design of more effective medical care models focused on the prevention, early detection, and treatment of AKI, especially in units where its impact is more significant, such as Oncology, Internal Medicine, and Digestive System Units, would improve patient safety and reduce associated costs. The variability observed in the incidence and consequences of AKI among the different units highlights the importance of an individualized approach to identify priority areas in need of intervention.

In this context, we propose that the proactive integration of the Nephrology Unit into the multidisciplinary care of AKI is essential. The experience and specific training of nephrologists promote greater diagnostic accuracy, the establishment of targeted treatments earlier, and the planning of adequate follow-up both during hospitalization and after discharge. This would not only contribute to the improvement in health outcomes in the short and long term but also positively influence the sustainability of the healthcare system by reducing the costs associated with AKI.

This research has not received specific support from public sector agencies, the commercial sector, or nonprofit entities.