Introduction

AKI is recognised as one of the major complications in hospitalised individuals imposing a substantial burden on patients and health care systems. The syndrome is associated with an increased risk of morbidity and mortality (1), progressive deterioration of renal function (2) and reduced quality of life(3-5). High costs of AKI-related inpatient care result from prolonged hospitalisations, additional examinations and complications such as the need for renal replacement therapy (RRT), and readmissions (6, 7). Strata of AKI severity have significant prognostic implication (2); however, the direct contribution of AKI to adverse events is difficult to establish. Studies over the last decade have identified complex and bidirectional interactions between the kidney and other remote organ systems, including heart, lungs, brain liver in the settings of AKI(8). As a result, the syndrome is often seen as a proxy of the underlying severity of illness (9)involving a spectrum of differing etiologies, pathophysiologies and clinical scenarios (10). Its epidemiological profile is highly dependent on patient characteristics and the setting in which occurs. Studies on AKI in specific clinical cohorts allow understanding the magnitude, clinical features and outcomes in local circumstances, thus providing essential information for prevention and treatment strategies. The objective of this study was to describe the occurrence of AKI in a general population of hospitalised patients and to characterise them with a distinction between AKI apparent at admission and acquired later during hospitalisation. We studied whether the two groups differed in baseline characteristics, AKI severity and short-term outcomes, namely the length of hospital stay, in-hospital and 6-month post-discharge mortality. Besides, in patients free of AKI at admission, we assessed how the risk of the development of the syndrome changes over hospital stay.