Acute Kidney Injury in Hospitalized Patients with Community-Acquired Pneumonia: Frequency, Factors Associated with AKI, and Clinical Outcomes

Background: Community-acquired pneumonia (CAP) is a common infectious disease associated with substantial morbidity and mortality. Acute kidney injury (AKI) is a frequent complication of CAP and may adversely affect clinical outcomes. This study aimed to determine the frequency of AKI and identify factors associated with AKI in hospitalized patients with CAP. Methods: This retrospective cohort study was conducted at a tertiary care university hospital in Türkiye and included patients aged >18 years hospitalized with CAP between July 2024 and July 2025. Only patients initially admitted to the general ward were included. Patients receiving dialysis for end-stage renal disease, those with active malignancy, those receiving immunosuppressive therapy, and those with incomplete data were excluded. Demographic characteristics, vital signs, laboratory findings, comorbidities, smoking status, and medication histories were recorded. AKI was defined according to KDIGO criteria using the closest clinically stable pre-admission serum creatinine value obtained within 7–365 days before hospitalization as baseline. Results: Among 161 patients, AKI was identified in 60 (37.3%), including 43 patients who fulfilled the KDIGO criteria at hospital admission and 17 who developed AKI during hospitalization. Eight patients with AKI (13.3%) required hemodialysis, although none became permanently dialysis-dependent. Patients with AKI had longer hospital stays (p = 0.038) and a greater need for intensive care (p = 0.028). They were older and had higher respiratory rates, blood urea nitrogen (BUN), and red cell distribution width (RDW) values and lower diastolic blood pressure. DM and CKD were more common in the AKI group. In multivariable analysis, confusion (adjusted OR 5.03, 95% CI 1.01–25.02; p = 0.048), CKD (adjusted OR 6.00, 95% CI 1.28–28.13; p = 0.023), and higher BUN levels (adjusted OR 1.095 per 1 mg/dL increase, 95% CI 1.046–1.146; p < 0.001) were independently associated with AKI. These associations were retained in a Firth penalized logistic regression sensitivity analysis. Conclusions: AKI was common among hospitalized patients with CAP and was associated with longer hospital stay and greater intensive care utilization. Confusion, pre-existing CKD, and elevated BUN levels were independently associated with AKI, whereas DM was not independently associated after multivariable adjustment. Given that most AKI cases were already present at hospital admission, these findings should be interpreted as associations rather than predictors of incident AKI.