The Risk and Burden of Acute Kidney Injury in elderly with Dementia

Technical Summary: The Risk and Burden of Acute Kidney Injury in Elderly with Dementia

Problem Statement
Advanced age is a shared risk factor for both dementia and acute kidney injury (AKI). While previous research has established that AKI increases the long-term risk of developing dementia, the reverse relationship—whether pre-existing dementia independently predisposes elderly patients to AKI—remains unclear. Dementia patients often suffer from impaired thirst perception, autonomic dysfunction, and medication management issues, which are known risk factors for AKI. However, existing evidence regarding the independent association between dementia and AKI incidence is limited. This study aims to investigate the epidemiology of AKI in elderly patients with pre-existing dementia, determine if dementia is an independent predictor of AKI, and assess the clinical and economic burden of comorbid AKI and dementia.

Methodology
This retrospective cohort study utilized data from the electronic health record repository of Guangdong Provincial People's Hospital, a single center within the larger China Collaborative Study on Acute Kidney Injury (CCS-AKI).

• Population: The study focused on inpatient episodes for patients aged 65 years and older admitted between January 1, 2012, and December 31, 2016. From an initial pool of 65,122 admissions, 54,319 met inclusion criteria (excluding those with missing outcomes, definitive diagnoses, insufficient creatinine measurements, end-stage renal disease, or dialysis prior to AKI diagnosis).
• Definitions:
  • AKI: Defined according to KDIGO 2012 guidelines (increase in serum creatinine ≥26.5 µmol/L within 48 hours or ≥1.5 times baseline within 7 days). Community-acquired (CA-AKI) and hospital-acquired (HA-AKI) were distinguished based on admission creatinine levels relative to the lowest in-hospital value.
  • Dementia: Identified via discharge diagnosis using specific International Classification of Diseases (ICD) codes (F00–F03, F051, G30, G311).
  • Comorbidities: Classified and scored using the Charlson Comorbidity Index (CCI).
• Statistical Analysis:
  • Propensity Score Matching (PSM): To minimize confounding, a 1:1 nearest-neighbor PSM was performed with a caliper of 0.1 standard deviations. Dementia patients were matched with non-dementia controls based on age, sex, and various comorbidities (e.g., hypertension, heart failure, diabetes, renal/liver disease, tumors).
  • Regression Models: Univariate and multivariable logistic regression models were employed to calculate odds ratios (OR) and 95% confidence intervals (CI) for the association between dementia and AKI, adjusting for demographics and comorbidities.
  • Outcomes: The study compared the incidence of AKI, length of stay (LOS), hospitalization costs, and in-hospital mortality between groups.

Key Results

• Incidence: Among the 54,319 included admissions, 2,977 (5.5%) experienced AKI, and 1,845 (3.4%) had a documented history of dementia.
• Association:
  • Unadjusted/PSM: After propensity score matching, the incidence of AKI was significantly higher in the dementia group (10.6%) compared to the non-dementia control group (7.1%). The odds ratio (OR) was 1.56 (95% CI 1.24–1.96).
  • Multivariable Analysis: In the fully adjusted multivariable logistic regression model (controlling for age, sex, hypertension, myocardial infarction, heart failure, cardiovascular disease, pulmonary disease, diabetes, renal/liver disease, and tumors), dementia remained an independent risk factor for AKI with an OR of 1.90 (95% CI 1.61–2.24).
  • Subgroup Analysis: The association was consistent across gender and hypertension status. The strongest association was observed in patients aged 75–84 years (OR 2.88), though it remained significant in those aged ≥85 years (OR 1.63).
• Clinical Burden: Patients with both AKI and dementia exhibited the most severe outcomes compared to those with only one condition or neither:
  • Length of Stay: Median 57.5 days (vs. 26.0 for AKI alone, 17.0 for dementia alone, 10.0 for neither).
  • Costs: Median ¥348,000 (vs. ¥117,000 for AKI alone, ¥56,000 for dementia alone, ¥32,000 for neither).
  • Mortality: In-hospital mortality was 31.6% for the comorbid group, compared to 16.6% for AKI alone, 2.7% for dementia alone, and 1.6% for neither.

Significance and Claims
The authors conclude that in a cohort of elderly admissions, pre-existing dementia is a strong and independent predictor of AKI. The study highlights that the co-occurrence of these conditions leads to the most detrimental resource utilization (longest stays, highest costs) and survival outcomes.

The paper posits that this association is likely driven by intersecting pathways, including dehydration due to impaired thirst perception, polypharmacy (specifically the use of atypical antipsychotics), autonomic dysfunction, and delayed recognition of urinary obstruction. Furthermore, the authors suggest that shared pathophysiological mechanisms, such as chronic inflammation and endothelial dysfunction, may link cerebral and renal injury.

Limitations and Scope
The authors explicitly acknowledge limitations, including the single-center, retrospective design which limits generalizability and causal inference. Dementia severity was not quantitatively assessed, potentially underestimating mild cases. Additionally, the use of the lowest inpatient creatinine as a baseline may have led to an overestimation of AKI incidence. The study does not propose specific new interventions but calls for the development and implementation of targeted nephroprotective strategies and integrated care models for this vulnerable population, emphasizing the need for routine cognitive screening and careful fluid/medication management in future clinical practice.