Abstract
Background
As life expectancy increases and more adults aged ≥ 65 years undergo continuous kidney replacement therapy (CKRT), grouping patients into narrower age groups—rather than treating those aged ≥ 65 years as a single category—can provide more precise insights into age-related mortality risks.
Methods
This consecutive, retrospective study examined adults aged ≥ 65 years who underwent CKRT for acute kidney injury (AKI) at a tertiary hospital between August 2017 and March 2024. Participants were stratified into three age groups; 65–74 years, 75–84 years, and ≥ 85 years. The outcomes included 48-hour, 7-day, and in-hospital mortality. Logistic regression analysis was used to identify the impact of stratified age on mortality and the factors associated with age-specific mortality in each group.
Results
Among the 1017 eligible patients, 292 (28.7%) died within 48 h, 402 (39.5%) within 7 days, and 607 (59.7%) during hospitalization. Compared with patients aged 65–74 years, those aged 75–84 years and those aged ≥ 85 years did not have an increased risk of 48-h, 7-day, or in-hospital mortality after adjustment for clinical variables. In patients aged 75–84 years, a higher serum albumin level was independently associated with lower in-hospital mortality (adjusted odds ratio [aOR], 0.35; 95% confidence interval [CI], 0.16–0.70; P = 0.004). In patients aged ≥ 85 years, a higher body mass index was significantly associated with reduced 7-day mortality (aOR, 0.74; 95% CI, 0.52–0.95; P = 0.037) and in-hospital mortality (aOR, 0.65; 95% CI, 0.43–0.87; P = 0.014).
Conclusions
In adults aged ≥ 65 years undergoing CKRT, advanced age was not associated with increased risk of early or in-hospital mortality. Among those aged ≥ 75 years, indicators of baseline health and nutrition status were associated with mortality. Age alone should not preclude CKRT decision-making in patients aged ≥ 65 years with AKI.
Keywords: 48-hour mortality, 7-day mortality, Acute kidney injury, Continuous kidney replacement therapy, In-hospital mortality, Adults aged ≥ 65 years
Background
As the life expectancy of humans increases, so does the number of older people. An aging society is defined as one in which adults aged ≥ 65 years comprise ≥ 7% of the population; an aged society. ≥ 14%; and a super aging society, ≥ 20% [1]. As the global population ages, older people present diverse medical conditions that vary by age [2]. To better understand these differences, it is necessary to classify older individuals by narrower age groups rather than treating them as a single demographic. In general, older adults are defined as 65 years of age or older, but there are differences in the additional classification of older people. In the American Geriatric Society and the World Health Organization, those over 80 years of age are further classified as oldest-old. In the British Geriatric Society, those over 85 years of age are classified as the oldest-old [3]. In studies of older people, 85 years of age was set as the cut-off value for the oldest-old [1, 4].
Adults aged ≥ 65 years are at increased risk of acute kidney injury (AKI) due to multiple comorbidities, polypharmacy, reduced kidney reserve, and heightened vulnerability to hemodynamic changes. Consequently, the incidence of AKI requiring continuous kidney replacement therapy (CKRT) is rising in this population [5]. In real-world clinical settings, medical staff and family members may perceive that adults aged ≥ 65 years experience poorer outcomes, and age may become an implicit barrier during to initiating CKRT. Although such clinical circumstances are common, few studies have examined the impact of age on mortality among adults aged ≥ 65 years receiving CKRT, and existing findings remain inconsistent [4, 6–8].
In this study, adults aged ≥ 65 years who underwent CKRT were stratified into three age groups (65–74 years, 75–84 years, and ≥ 85 years) to assess the impact of age on early mortality (48-h and 7-day) and in-hospital mortality, as well as to identifyand the factors associated with early mortality in each group.
Methods
Study participants
This consecutive, retrospective study examined patients who underwent CKRT at a tertiary hospital between August 2017 and March 2024. Among 1940 individuals who received CKRT, 1017 adults aged ≥ 65 years with AKI were included after excluding 714 individuals aged < 65 years and 209 with end-stage kidney disease receiving maintenance dialysis (Fig. 1). Patients with advanced heart failure were not excluded if they met the clinical indication for CKRT. The remaining participants were grouped by age as follows: 65–74 years, 75–84 years, and 85 years or older.
Fig. 1.
Study inclusion flow chart. Out of a total of 1940 individuals receiving CKRT, 1017 patients aged ≥ 65 years were incorporated into this study after excluding 714 patients below the age of 65 and 209 patients with ESKD who were undergoing maintenance dialysis. Abbreviations: CKRT, continuous kidney replacement therapy; ESKD, end-stage kidney disease; KNUH, Kyungpook National University Hospital
CKRT protocol
CKRT was started by a nephrologist based on the indications of volume overload, hyperkalemia, metabolic acidosis, or oliguria. Continuous venovenous hemodiafiltration was conducted on all patients utilizing either the PRISMAFLEX system (Gambro, Germany) or the multiFiltrate platform (Fresenius Medical Care, Germany). CKRT was initiated with a blood flow rate set at 100 mL/min, which was progressively raised to 150 mL/min and modified based on the hemodynamic condition. Effluent volume was prescribed to achieve a dose of more than 35 mL/kg/h and adjusted according to the acid-base status. All patients who required CKRT were admitted to the intensive care unit and received CKRT.
Outcomes and variables
Outcomes were 48-h, 7-day, and in-hospital mortality. Variables included age, sex, body mass index (BMI), comorbidities, Charlson Comorbidity Index (CCI), Sequential Organ Failure Assessment (SOFA) score at the time of CKRT initiation, laboratory findings, and CKRT information (i.e., prescribed effluent dose, anticoagulation type, and dialysis catheter type). The severity of comorbid conditions was assessed using the CCI, a validated scoring system in which higher scores reflect greater comorbidity burden and are associated with poorer clinical outcomes [9].
Statistical analysis
Continuous variables were expressed as their mean ± standard deviation or as their median with the interquartile range. Intergroup differences were assessed using one-way analysis of variance for continuous variables and the Pearson chi-square test or Fisher’s exact test for categorical variables. The Bonferroni correction was applied to P values for all pairwise comparisons among the three age groups. When comparing mortality proportions across age groups with unequal sample sizes, proportion tests were used. Logistic regression analysis was used to determine the impact of stratified age on 48-h, 7-day, and in-hospital mortality and the factors associated with age-specific mortality in each group. Confounding factors included age, sex, BMI, CCI, serum albumin level, serum lactate level, prescribed effluent dose, and SOFA score. Statistical analyses were performed using SAS for Windows, version 9.4 (SAS Institute, Cary, NC, USA) and R, version 4.4.1 (R Foundation for Statistical Computing, Vienna, Austria). Statistical significance was set at P < 0.05.
Results
Baseline characteristics
The baseline characteristics of each group are displayed in Table 1. The mean age was 76.4 ± 6.8 years, and 58.2% were male. The mean BMI was 23.0 ± 3.9 kg/m2, and the mean SOFA score was 12.4 ± 4.5. The mean serum blood urea nitrogen (BUN) level, serum albumin level, and serum lactate level were 61.1 ± 33.7 mg/dL, 3.0 ± 0.7 g/dL, and 6.7 ± 5.8 mmol/L, respectively. The mean prescribed effluent dose of CKRT was 35.2 ± 8.6 ml/kg/hr. When patients were stratified by age, 421 (41.4%) were assigned to the 65–74-year group, 461 (45.3%) to the 75–84-year group, and 135 (13.3%) to the ≥ 85-years group. Statistically significant differences were observed between groups in the following variables: sex (P = 0.033), BMI (P < 0.001), comorbidities such as hypertension (P = 0.001) and congestive heart failure (P = 0.031), SOFA score (P = 0.015), use of mechanical ventilation (P < 0.001), BUN levels (P = 0.02), PCO2 levels (P = 0.007), and type of anticoagulation administered (P < 0.001).
Table 1.
Baseline patient characteristics
| Variables | Total (n = 1017) | 65 ≤ Age < 75 (n = 421) | 75 ≤ Age < 85 (n = 461) | Age ≥ 85 (n = 135) | P value |
|---|---|---|---|---|---|
| Age, years | 76.4 ± 6.8 | 69.6 ± 2.9 | 79.3 ± 2.9 | 87.5 ± 2.2 | < 0.001 |
| Male | 592 (58.2%) | 256 (60.8%)a | 271 (58.8%) | 65 (48.1%)a | 0.033 |
| BMI, kg/m2 | 23.0 ± 3.9 | 23.6 ± 3.9a, b | 22.9 ± 4.0a | 21.9 ± 3.7b | < 0.001 |
| Comorbidities | |||||
| Diabetes mellitus | 377 (37.1%) | 155 (36.8%) | 172 (37.3%) | 50 (37.0%) | 0.989 |
| Hypertension | 524 (52.1%) | 191 (46.0%)a, b | 249 (54.5%)a | 84 (62.7%)b | 0.001 |
| Chronic pulmonary disease | 38 (3.7%) | 16 (3.8%) | 19 (4.1%) | 3 (2.2%) | 0.590 |
| Liver disease | 20 (2.0%) | 10 (2.4%) | 8 (1.7%) | 2 (1.5%) | 0.720 |
| Myocardial infarction | 171 (16.8%) | 77 (18.3%) | 73 (15.8%) | 21 (15.6%) | 0.570 |
| Congestive heart failure | 138 (13.6%) | 43 (10.2%)a | 73 (15.8%)a | 22 (16.3%) | 0.031 |
| Peripheral vascular disease | 31 (3.0%) | 11 (2.6%) | 14 (3.0%) | 6 (4.4%) | 0.560 |
| Cerebrovascular accident | 137 (13.5%) | 48 (11.4%) | 70 (15.2%) | 19 (14.1%) | 0.253 |
| Malignancy | 86 (8.5%) | 33 (7.8%) | 40 (8.7%) | 13 (9.6%) | 0.788 |
| Charlson Comorbidity Index | 2.0 (1.0–3.0) | 2.0 (1.0–3.0) | 2.0 (1.0–3.0) | 2.0 (1.0–3.0) | 0.992 |
|
Time from ICU admission to CKRT initiation, days |
1.0 (1.0–2.0) | 1.0 (1.0–2.0) | 1.0 (1.0–2.0) | 1.0 (1.0–3.0) | 0.333 |
| SOFA score | 12.4 ± 4.5 | 12.9 ± 4.4a | 12.0 ± 4.6a | 12.4 ± 4.0 | 0.015 |
| Need for mechanical ventilation | 616 (60.6%) | 289 (68.6%)a, b | 263 (57.2%)a | 64 (47.4%)b | < 0.001 |
| Laboratory findings | |||||
| WBC, 103/µL | 13.9 ± 10.2 | 13.3 ± 9.7 | 14.1 ± 10.8 | 14.8 ± 9.9 | 0.254 |
| Hemoglobin, g/dL | 10.2 ± 2.5 | 10.2 ± 2.6 | 10.2 ± 2.5 | 10.2 ± 2.3 | 0.979 |
| Platelet, 103/µL | 155.7 ± 107.6 | 149.8 ± 114.1 | 155.4 ± 101.8 | 175.3 ± 104.5 | 0.056 |
| Sodium, mmol/L | 137.5 ± 7.5 | 137.3 ± 7.5 | 137.6 ± 7.4 | 137.8 ± 7.7 | 0.759 |
| Potassium, mmol/L | 4.8 ± 1.6 | 4.8 ± 2.1 | 4.8 ± 1.1 | 4.9 ± 1.0 | 0.827 |
| BUN, mg/dL | 61.1 ± 33.7 | 58.4 ± 33.3a | 61.7 ± 34.3 | 67.6 ± 32.3a | 0.020 |
| Creatinine, mg/dL | 3.5 ± 2.7 | 3.6 ± 3.4 | 3.5 ± 2.2 | 3.6 ± 2.1 | 0.767 |
| Albumin, g/dL | 3.0 ± 0.7 | 3.0 ± 0.7 | 3.0 ± 0.7 | 3.0 ± 0.6 | 0.882 |
| INR | 1.8 ± 1.2 | 1.9 ± 1.6 | 1.7 ± 0.9 | 1.7 ± 0.8 | 0.249 |
| aPTT, sec | 42.6 ± 21.1 | 43.6 ± 22.2 | 41.8 ± 20.1 | 41.9 ± 20.9 | 0.520 |
| Arterial pH | 7.3 ± 0.2 | 7.3 ± 0.1 | 7.3 ± 0.3 | 7.3 ± 0.3 | 0.938 |
| PCO2, mmHg | 36.4 ± 12.9 | 38.0 ± 14.1a | 35.1 ± 11.9a | 35.2 ± 11.6 | 0.007 |
| PO2, mmHg | 112.1 ± 60.3 | 111.2 ± 62.7 | 113.2 ± 58.5 | 111.1 ± 59.0 | 0.885 |
| HCO3-, mmol/L | 17.1 ± 6.6 | 17.2 ± 5.6 | 16.8 ± 6.5 | 17.9 ± 8.9 | 0.204 |
| Lactate, mmol/L | 6.7 ± 5.8 | 6.5 ± 5.7 | 7.1 ± 6.1 | 6.4 ± 5.3 | 0.559 |
| CKRT information | |||||
| Prescribed effluent dose, ml/kg/hr | 35.2 ± 8.6 | 34.6 ± 8.1 | 35.5 ± 9.3 | 36.1 ± 6.7 | 0.152 |
| Anticoagulation type | < 0.001 | ||||
| Heparin free | 557 (54.8%) | 255 (60.6%)a | 243 (52.7%)b | 59 (44.0%)a, b | |
| Heparin | 270 (26.6%) | 86 (20.4%) | 128 (27.8%) | 56 (41.8%) | |
| Nafamostat mesilate | 189 (18.6%) | 80 (19.0%) | 90 (19.5%) | 19 (14.2%) | |
| Dialysis catheter type | |||||
| Nontunneled noncuffed catheter | 971 (96.9%) | 398 (96.4%) | 446 (97.6%) | 127 (96.2%) | 0.287 |
| Cuffed tunneled catheter | 22 (2.2%) | 11 (2.7%) | 6 (1.3%) | 5 (3.8%) | |
| ECMO | 9 (0.9%) | 4 (1.0%) | 5 (1.1%) | 0 (0.0%) |
Values are provided as the mean ± standard deviation, number (%), or median (interquartile range)
Abbreviations: aPTT, activated partial thromboplastin time; BMI, body mass index; BUN, blood urea nitrogen; CKRT, continuous kidney replacement therapy; ECMO, extracorporeal membrane oxygenation; ICU, intensive care unit; INR, international normalized ratio; SOFA, sequential organ failure assessment; WBC, white blood cell
A superscript marked with a or b is the case where the difference between values marked with the same superscript is P < 0.05
Early and in-hospital mortality
Among the 1017 patients who underwent CKRT, 292 (28.7%) died within 48 h, 402 (39.5%) within 7 days, and 607 (59.7%) during hospitalization. The 48-h mortality rates were 26.6% in the 65–74-year group, 29.7% in the 75–84-year group, and 31.9% in the ≥ 85-year group. The 7-day mortality rates were 38.7%, 38.6%, and 45.2% in the 65–74-year, 75–84 year, and ≥ 85-year groups, respectively. In-hospital mortality occurred in 57.7% of the 65–74-year group, 62.0% of the 75–84-year group, and 57.8% of the ≥ 85-year group (Fig. 2). The incidence of each mortality outcome did not differ significantly among age groups.
Fig. 2.
The 48-h, 7-day, and in-hospital mortality rates of adults aged ≥ 65 years receiving CKRT by age group. 292 (28.7%) 48-h deaths, 402 (39.5%) 7-day deaths, and 607 (59.7%) in-hospital deaths occurred. The 48-h mortality rates were 26.6% in the 65–74-year group, 29.7% in the 75–84-year group, and 31.9% in the ≥ 85-year group (P = 0.408). The 7-day mortality rates were 38.7%, 38.6%, and 45.2% in the 65–74-year, 75–84-year, and ≥ 85-year groups, respectively (P = 0.353). In-hospital mortality was observed in 57.7% of the 65–74-year group, 62.0% of the 75–84-year group, and 57.8% of the ≥ 85-year group (P = 0.379). Abbreviations: CKRT, continuous kidney replacement therapy
Association between stratified age and early and in-hospital mortality
Multivariate logistic regression analysis was used to determine the association between stratified age and 48-h, 7-day, and in-hospital mortality (Table 2). Compared with the 65–74-year group, the 75–84-year and ≥ 85-year groups were not independently associated with increased risk of 48-h, 7-day, or in-hospital mortality, even after adjusting for several clinical variables, including BMI, CCI, serum albumin level, serum lactate level, prescribed effluent dose, and SOFA score.
Table 2.
Factors associated with mortality among acute kidney injury patients
| 48-hour mortality | 7-day mortality | In-hospital mortality | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Variables | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value |
| Age | ||||||||||||
| 65 ≤ Age < 75 | Reference | - | Reference | - | Reference | - | Reference | - | Reference | - | Reference | - |
| 75 ≤ Age < 85 | 1.17 (0.87–1.57) | 0.305 | 1.31 (0.73–2.36) | 0.360 | 1.03 (0.78–1.37) | 0.840 | 1.10 (0.62–1.94) | 0.753 | 1.20 (0.91–1.57) | 0.191 | 1.75 (0.98–3.13) | 0.058 |
| Age ≥ 85 | 1.29 (0.84–1.96) | 0.237 | 1.77 (0.75–4.12) | 0.187 | 1.41 (0.93–2.13) | 0.108 | 1.04 (0.44–2.41) | 0.933 | 1.00 (0.68–1.49) | 0.991 | 0.72 (0.31–1.67) | 0.445 |
| Male vs. Female | 1.08 (0.82–1.43) | 0.572 | 1.26 (0.70–2.27) | 0.442 | 0.80 (0.61–1.05) | 0.102 | 0.69 (0.38–1.22) | 0.200 | 1.05 (0.81–1.35) | 0.730 | 0.94 (0.52–1.67) | 0.826 |
| BMI | 0.99 (0.96–1.03) | 0.638 | 0.99 (0.91–1.08) | 0.879 | 0.99 (0.95–1.03) | 0.526 | 0.97 (0.89–1.05) | 0.412 | 1.00 (0.96–1.03) | 0.864 | 0.96 (0.88–1.04) | 0.303 |
| Charlson Comorbidity Index | 1.01 (0.93–1.09) | 0.805 | 0.91 (0.76–1.09) | 0.312 | 0.99 (0.92–1.07) | 0.845 | 1.02 (0.85–1.22) | 0.814 | 0.99 (0.92–1.07) | 0.814 | 0.98 (0.82–1.16) | 0.800 |
| BUN | 1.00 (1.00–1.01) | 0.109 | 1.00 (0.99–1.01) | 0.906 | 1.00 (1.00–1.01) | 0.049 | 1.01 (1.00–1.01) | 0.145 | 1.00 (1.00–1.01) | 0.749 | 1.00 (0.99–1.01) | 0.897 |
| Albumin | 0.96 (0.77–1.19) | 0.715 | 0.73 (0.48–1.10) | 0.139 | 0.93 (0.75–1.14) | 0.476 | 0.91 (0.60–1.38) | 0.657 | 0.78 (0.64–0.96) | 0.018 | 0.65 (0.42–0.99) | 0.046 |
| Lactate | 1.03 (0.99–1.06) | 0.165 | 1.00 (0.95–1.05) | 0.992 | 1.03 (1.00–1.07) | 0.080 | 1.02 (0.97–1.07) | 0.509 | 1.04 (1.00–1.08) | 0.039 | 1.03 (0.98–1.09) | 0.225 |
| Prescribed effluent dose | 0.99 (0.97–1.01) | 0.269 | 0.99 (0.96–1.03) | 0.606 | 1.00 (0.98–1.02) | 0.887 | 0.98 (0.95–1.02) | 0.369 | 1.00 (0.98–1.01) | 0.531 | 0.98(0.95–1.02) | 0.318 |
| SOFA score | 1.00 (0.97–1.03) | 0.949 | 1.00 (0.93–1.08) | 0.937 | 1.01 (0.98–1.04) | 0.571 | 0.99 (0.91–1.07) | 0.734 | 1.01 (0.98–1.04) | 0.464 | 0.94 (0.86–1.01) | 0.094 |
a Adjusted for age, sex, BMI, Charlson Comorbidity Index, BUN, albumin, lactate, prescribed effluent dose, and SOFA score
Abbreviations: BUN, blood urea nitrogen; CI, confidence interval; OR, odds ratio; SOFA, sequential organ failure assessment
Factors associated with early and in-hospital mortality in each group
Multivariate logistic regression analysis was used to identify the factors associated with age-specific mortality in the 65–74-year group (Table 3), the 75–84-year group (Table 4), and the ≥ 85-year group (Table 5).
Table 3.
Factors associated with mortality among acute kidney injury patients aged 65 to 75
| 48-hour mortality | 7-day mortality | In-hospital mortality | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Variables | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value |
| Male vs. Female | 1.36 (0.87–2.15) | 0.184 | 1.00 (0.39–2.67) | 0.998 | 0.83 (0.54–1.26) | 0.372 | 0.67 (0.26–1.67) | 0.389 | 0.97 (0.65–1.44) | 0.878 | 0.60 (0.24–1.48) | 0.273 |
| BMI | 0.97 (0.92–1.03) | 0.382 | 0.97 (0.83–1.13) | 0.669 | 1.00 (0.94–1.06) | 0.985 | 1.00 (0.26–1.67) | 0.960 | 1.01 (0.96–1.07) | 0.704 | 0.99 (0.85–1.15) | 0.893 |
| Charlson Comorbidity Index | 1.03 (0.91–1.16) | 0.643 | 1.02 (0.77–1.33) | 0.885 | 0.95 (0.85–1.07) | 0.410 | 0.98 (0.74–1.27) | 0.857 | 0.96 (0.86–1.07) | 0.449 | 0.93 (0.72–1.19) | 0.559 |
| BUN | 1.01 (1.00–1.01) | 0.062 | 1.01 (1.00–1.02) | 0.203 | 1.01 (1.00–1.02) | 0.013 | 1.01 (1.00–1.03) | 0.093 | 1.01 (1.00–1.01) | 0.030 | 1.00 (0.99–1.02) | 0.419 |
| Albumin | 0.96 (0.68–1.35) | 0.802 | 0.96 (0.47–1.92) | 0.900 | 1.07 (0.77–1.48) | 0.695 | 1.64 (0.80–3.51) | 0.184 | 0.86 (0.63–1.18) | 0.353 | 1.16 (0.59–2.30) | 0.670 |
| Lactate | 1.04 (0.99–1.10) | 0.131 | 0.99 (0.90–1.08) | 0.834 | 1.06 (1.00–1.12) | 0.065 | 1.02 (0.93–1.12) | 0.647 | 1.10 (1.04–1.18) | 0.004 | 1.11 (1.02–1.23) | 0.026 |
| Prescribed effluent dose | 0.99 (0.96–1.02) | 0.354 | 0.97 (0.92–1.02) | 0.280 | 1.00 (0.97–1.03) | 0.941 | 0.99 (0.95–1.05) | 0.832 | 1.00 (0.98–1.03) | 0.799 | 0.99 (0.94–1.04) | 0.584 |
| SOFA score | 1.02 (0.97–1.08) | 0.497 | 0.98 (0.87–1.10) | 0.702 | 1.04 (0.99–1.09) | 0.177 | 0.98 (0.88–1.10) | 0.773 | 1.02 (0.97–1.07) | 0.523 | 0.91 (0.81–1.02) | 0.139 |
a Adjusted for sex, BMI, Charlson Comorbidity Index, BUN, albumin, lactate, prescribed effluent dose, and SOFA score
Abbreviations: BUN, blood urea nitrogen; CI, confidence interval; OR, odds ratio; SOFA, sequential organ failure assessment
Table 4.
Factors associated with mortality among acute kidney injury patients aged 75 to 85
| 48-hour mortality | 7-day mortality | In-hospital mortality | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Variables | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value |
| Male vs. Female | 0.86 (0.57–1.29) | 0.464 | 2.47 (0.97–6.74) | 0.065 | 0.62 (0.42–0.93) | 0.020 | 0.73 (0.29–1.83) | 0.498 | 1.00 (0.68–1.46) | 0.980 | 2.02 (0.76–5.56) | 0.162 |
| BMI | 1.01 (0.96–1.07) | 0.723 | 1.09 (0.96–1.25) | 0.181 | 0.99 (0.94–1.04) | 0.655 | 1.01 (0.89–1.15) | 0.873 | 1.00 (0.95–1.05) | 0.847 | 1.05 (0.92–1.21) | 0.475 |
| Charlson Comorbidity Index | 1.03 (0.91–1.15) | 0.647 | 0.87 (0.66–1.14) | 0.324 | 1.04 (0.93–1.17) | 0.482 | 1.12 (0.85–1.48) | 0.440 | 1.01 (0.90–1.13) | 0.882 | 1.06 (0.78–1.47) | 0.714 |
| BUN | 1.00 (0.99–1.01) | 0.726 | 0.98 (0.97–1.00) | 0.034 | 1.00 (1.00–1.01) | 0.738 | 1.00 (0.99–1.01) | 0.904 | 1.00 (0.99–1.00) | 0.133 | 0.99 (0.97–1.00) | 0.070 |
| Albumin | 0.95 (0.70–1.30) | 0.760 | 0.57 (0.30–1.04) | 0.070 | 0.83 (0.61–1.12) | 0.225 | 0.60 (0.32–1.09) | 0.099 | 0.77 (0.57–1.04) | 0.525 | 0.35 (0.16–0.70) | 0.004 |
| Lactate | 1.03 (0.97–1.08) | 0.338 | 1.00 (0.92–1.07) | 0.909 | 1.01 (0.96–1.07) | 0.628 | 1.01 (0.94–1.09) | 0.689 | 0.99 (0.94–1.03) | 0.525 | 0.95 (0.88–1.03) | 0.252 |
| Prescribed effluent dose | 1.00 (0.98–1.02) | 0.914 | 1.04 (0.99–1.10) | 0.127 | 1.01 (0.98–1.03) | 0.637 | 0.99 (0.94–1.05) | 0.807 | 0.99 (0.97–1.02) | 0.582 | 1.01 (0.95–1.07) | 0.715 |
| SOFA score | 0.99 (0.94–1.03) | 0.564 | 1.07 (0.94–1.22) | 0.313 | 0.99 (0.94–1.03) | 0.536 | 1.01 (0.90–1.15) | 0.827 | 1.01 (0.96–1.06) | 0.661 | 0.98 (0.86–1.12) | 0.782 |
a Adjusted for sex, BMI, Charlson Comorbidity Index, BUN, albumin, lactate, prescribed effluent dose, and SOFA score
Abbreviations: BUN, blood urea nitrogen; CI, confidence interval; OR, odds ratio; SOFA, sequential organ failure assessment
Table 5.
Factors associated with mortality among acute kidney injury patients aged ≥ 85
| 48-hour mortality | 7-day mortality | In-hospital mortality | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Variables | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value | Crude OR (95% CI) | P value | Adjusted ORa (95% CI) | P value |
| Male vs. Female | 1.37 (0.66–2.85) | 0.397 | 0.27 (0.02–2.14) | 0.266 | 1.84 (0.89–3.86) | 0.101 | 0.90 (0.14–5.04) | 0.901 | 1.52 (0.77–3.05) | 0.231 | 0.80 (0.10–5.47) | 0.821 |
| BMI | 1.00 (0.90–1.12) | 0.961 | 0.76 (0.54–0.99) | 0.066 | 0.99 (0.88–1.10) | 0.782 | 0.74 (0.52–0.95) | 0.037 | 0.98 (0.88–1.08) | 0.642 | 0.65 (0.43–0.87) | 0.014 |
| Charlson Comorbidity Index | 0.89 (0.70–1.12) | 0.324 | 0.53 (0.21–1.14) | 0.131 | 0.97 (0.76–1.24) | 0.818 | 1.23 (0.57–2.95) | 0.606 | 1.06 (0.86–1.33) | 0.579 | 1.02 (0.47–2.30) | 0.953 |
| BUN | 1.01 (1.00–1.02) | 0.075 | 1.02 (0.99–1.05) | 0.206 | 1.00 (0.99–1.02) | 0.706 | 1.00 (0.98–1.03) | 0.904 | 1.00 (0.99–1.01) | 0.671 | 1.01 (0.98–1.04) | 0.484 |
| Albumin | 0.99 (0.53–1.88) | 0.981 | 1.73 (0.22–21.63) | 0.626 | 0.85 (0.44–1.61) | 0.609 | 1.27 (0.22–8.05) | 0.788 | 0.56 (0.29–1.05) | 0.077 | 0.58 (0.07–3.98) | 0.571 |
| Lactate | 0.96 (0.86–1.07) | 0.508 | 0.90 (0.71–1.11) | 0.328 | 1.04 (0.94–1.16) | 0.413 | 1.00 (0.81–1.24) | 0.975 | 1.09 (0.98–1.22) | 0.115 | 1.12 (0.91–1.43) | 0.307 |
| Prescribed effluent dose | 0.92 (0.86–0.98) | 0.017 | 0.82 (0.64–0.99) | 0.067 | 0.95 (0.89–1.01) | 0.083 | 0.87 (0.71–1.01) | 0.102 | 0.96 (0.90–1.01) | 0.147 | 0.84 (0.67–1.01) | 0.100 |
| SOFA score | 1.01 (0.91–1.12) | 0.932 | 1.14 (0.78–1.66) | 0.455 | 1.04 (0.94–1.17) | 0.443 | 1.04 (0.69–1.61) | 0.867 | 1.04 (0.95–1.16) | 0.395 | 0.94 (0.66–1.24) | 0.704 |
a Adjusted for sex, BMI, Charlson Comorbidity Index, BUN, albumin, lactate, prescribed effluent dose, and SOFA score
Abbreviations: BUN, blood urea nitrogen; CI, confidence interval; OR, odds ratio; SOFA, sequential organ failure assessment
In the 65–74-year group, higher serum lactate levels were significantly associated increased in-hospital mortality (adjusted odds ratio [aOR], 1.11; 95% confidence interval [CI], 1.02–1.23; P = 0.026) (Table 3). In the 75–84-year group, higher serum albumin levels were independently associated with lower in-hospital mortality (aOR, 0.35; 95% CI, 0.16–0.70; P = 0.004) (Table 4). In the ≥ 85-year group, higher BMI was significantly associated with reduced 7-day mortality (aOR, 0.74; 95% CI, 0.52–0.95; P = 0.037) and in-hospital mortality (aOR, 0.65; 95% CI, 0.43–0.87; P = 0.014) (Table 5).
Discussion
This study included 1017 adults aged ≥ 65 years who underwent CKRT. Participants were stratified into three age groups: 65–74 years, 75–84 years, and ≥ 85 years. The study examined how age stratification affected mortality outcomes at 48 h, 7 days, and during hospitalization. We found that stratified age itself was not significantly associated with short-term and in-hospital death, even after adjusting for several clinical variables. However, when age-specific mortality factors were analyzed, higher serum albumin levels in the 75–84-year group and higher BMI in the ≥ 85-year group were significantly and independently associated with in-hospital death in patients receiving CKRT rather than acute illness parameters.
CKRT is the preferred treatment of choice for AKI patients with hemodynamic instability, and its utilization is increasing over time along with improvements in patient survival and recovery of kidney function [5, 10]. However, the in-hospital mortality rate of AKI patients undergoing CKRT was reported to be as high as 38.6% to 62.4% [11]. In this study of adults aged ≥ 65 years, the in-hospital mortality rate was 59.7%, consistent with findings from previous studies that included patients of all ages. In general, in studies including patients of all ages, advanced age is a well-known factor associated with poor outcomes in patients undergoing CKRT [12, 13]. However, contrary to expectations, the study, which included only patients aged ≥ 65 years receiving CKRT, did not find older age to be associated with higher mortality rates. No significant differences were observed in 48-h, 7-day, or in-hospital mortality rates among the 65–74-year, 75–84-year, and ≥ 85-year groups.
Few studies have specifically examined mortality by stratified age among adults aged ≥ 65 years undergoing CKRT, and the findings have been inconsistent. One study of 480 patients aged ≥ 65 years with AKI receiving CKRT reported that age >75 years was not associated with increased mortality at 28 or 90 days compared with those aged 65–74 years [6]. Other studies found that age alone was not a significant factor in increased mortality, including one involving 41 adults aged 80 to 100 who underwent CKRT [7] and another comparing mortality rates in patients over 75 versus under 75 years [8]. Conversely, a study comparing patients aged ≥ 65 years undergoing CKRT with middle-aged patients aged 55–64 years found that the middle-old and oldest-old groups had higher short- and long-term mortality rates [4]. The primary difference in findings across studies likely stems from variation in the control age group used for comparison. As life expectancy continues to rise, stratifying patients aged ≥ 65 years into narrower age ranges, as done in this study, provides more meaningful insights into clinical outcomes than treating them as a single demographic group. Comparing outcomes within the ≥ 65-year population undergoing CKRT yields more clinically relevant data than comparisons between those ≥ 65 years and those < 65 years. In this study, after adjusting for multiple clinical variables, neither the 75–84-year group nor the ≥ 85-year group demonstrated significantly higher rates of short-term or in-hospital mortality compared with the 65–74-year group. These findings suggest that clinicians should not avoid CKRT simply due to advanced age.
Factors associated with mortality have been reported in critically ill patients undergoing CKRT [11, 14, 15]. However, none of these studies have identified factors related to age-specific mortality among adults aged ≥ 65 years undergoing CKRT. In this study, participants aged ≥ 65 years receiving CKRT were stratified into three age groups: 65–74 years, 75–84 years, and ≥ 85 years. Mortality-related factors were analyzed within each group, revealing distinct associations by age. Among the 65–74-year group, the relatively younger subset of adults aged ≥ 65 years, acute illness parameters, particularly elevated serum lactate levels, were significantly linked to an increased in-hospital mortality. Hyperlactatemia often caused by hypoxemia-related lactate overproduction or impaired clearance [16, 17], has been previously associated with higher mortality across multiple clinical conditions, including CKRT, trauma, burns, and post-operation [18–21]. In our study, serum lactate levels were generally elevated, reflecting the severity of critical illness; however, no significant differences were observed across age groups. This suggests that lactate elevation was a common finding among all adults aged ≥ 65 years and was unlikely to have disproportionately influenced the decision to initiate CKRT.
In patients over 75 years of age, severity indicators such as SOFA scores and serum lactate levels were not significantly associated with in-hospital mortality. Instead, factors indicating chronic health or nutritional status, such as higher serum albumin levels in the 75–84-year group and elevated BMI in the ≥ 85-year group, were linked to lower in-hospital mortality. These finding suggests that baseline health status among patients aged ≥ 65 years receiving CKRT may be more predictive fo clinical prognosis than the severity of acute illness. Albumin is a major serum protein involved in maintaining plasma colloid osmotic pressure, maintaining homeostasis between intracellular fluid, extracellular fluid, and tissue fluid, and is involved in material transport in blood circulation [22, 23]. Previous studies have reported that hypoalbuminemia is associated with increased mortality in patients with septic shock, heart failure, acute coronary syndrome, and critically ill patients undergoing CKRT [24–31]. Similarly, in this study, higher albumin levels in the 75–84-year group undergoing CKRT were associated with lower in-hospital mortality. These results can be explained by the fact that hypoalbuminemia is associated with fluid shifting from the intravascular compartment to the extravascular compartment and a decrease in mean arterial pressure because albumin is a protein that regulates colloid oncotic pressure and intracellular volume [22, 23]. In addition, hypoalbuminemia and high mortality can also be explained by the fact that albumin is an indicator of nutritional status and inflammatory status. Hypoalbuminemia is associated with a pro-inflammatory state that produces endotoxins, chemokines, and cytokines. These inflammatory mediators inhibit albumin synthesis and eventually cause fluid excess, which leads to increased mortality [27, 32].
In a previous meta-analysis, BMI and all-cause mortality were reported to show a U-shape relationship, and in particular, a BMI value of less than 20 kg/m2 was reported to be associated with the highest risk of death [33]. Previous studies of critically ill patients undergoing CKRT also reported that a high BMI was associated with a lower mortality rate. Similarly, in this study, higher BMI was associated with lower in-hospital mortality in the ≥ 85-year group undergoing CKRT [34, 35], which could be explained by low BMI that would be attributable to cachexia, which is a complication of chronic disease. It is also known that underweight and malnutrition are associated with inflammation and deterioration of immune system functions [33, 36]. The association between low BMI and increased mortality in the ≥ 85-year group undergoing CKRT may be attributable to sarcopenia in addition to cachexia. Sarcopenia is defined as the progressive loss of muscle mass and strength, with associated risks of disability, poor quality of life and death [37]. Notably, greater muscle mass has been reported to exert protective effects on mortality in patients with AKI requiring CKRT [38]. However, BMI has clear limitations in reflecting sarcopenia, as it does not account for body composition. Indicators such as handgrip strength or weight-hip ratio, though challenging to implement in critically ill patients, may offer a more comprehensive assessment of mortality-related factors in this population. Severe cognitive impairment, although not evaluated in this study, may contribute to underweight and malnutrition through reduced oral intake, therby exacerbating sarcopenia and frailty and ultimately leading to poor clinical outcomes [39]. Future research should explore whether assessment and targeted intervention to improve cognitive function can mitigate sarcopenia and enhance survival in patients with advanced age undergoing CKRT.
This study has several limitations. First, its retrospective design may have introduced selection bias, as it included only patients aged ≥ 65 years who actually received CKRT. Importantly, we were unable to account for patients who were considered for CKRT but ultimately did not undergo treatment due to clinician judgment, comorbid conditions, patient or family refusal, or advanced care planning. These factors may have influenced the initiation or continuation of CKRT, especially in patients aged ≥ 65 years, where overall clinical condition and goals of care likely played a decisive role. Second, although many clinical variables were adjusted for, some may not have been accounted for, potentially influencing the results. Third, as a single-center study, the findings may not be fully generalizable to medical institutions with differing clinical practices or patient populations. Fourth, the focus was limited to early and in-hospital mortality, without evaluation of long-term outcomes. Fifth, long-term renal recovery among patients aged ≥ 65 years was not assessed. Future studies will need to look not only at long-term renal recovery but also at various clinical parameters such as frailty status, nutritional biomarkers, and treatment intensity to develop detailed therapeutic strategies for this population aged ≥ 65 years receiving CKRT. Lastly, another important limitation is that the etiology of AKI could not be consistently determined due to the retrospective nature of the database. Because different causes of AKI may influence outcomes, the inability to account for etiology may have affected our findings. Future prospective studies with detailed clinical data are needed to clarify the impact of AKI etiology in patients aged ≥ 65 years undergoing CKRT.
Despite these limitations, the study has several strengths. First, although the number of patients aged ≥ 65 years receiving CKRT is increasing, few studies have investigated the impact of age on mortality within this population. This study presents practical evidence that advanced age alone is not a significant determinant of mortality in patients aged ≥ 65 years receiving CKRT, offering relevant guidance for real-world clinical decision-making. Second, in this study, conclusions were drawn from data on more than 1000 patients aged ≥ 65 years who underwent CKRT, enhancing the robustness of the findings. Third, by identifying age-specific mortality risk factors, the study allows clinicians to better recognize patients at elevated risk and implement proactive, targeted interventions.
Conclusions
Among adults aged ≥ 65 years receiving CKRT, advanced age alone was not associated with increased risk of early or in-hospital death. In patients aged ≥ 75 years, indicators of chronic health and nutritional status, such as serum albumin levels in patients aged 75–84 years and BMI in those aged ≥ 85 years, were more closely associated with mortality than markers of acute illness. These findings suggest that age should not serve as a barrier to CKRT medical decision-making in patients aged ≥ 65 years with AKI.
Abbreviations
- AKI
Acute kidney injury
- BMI
Body mass index
- BUN
Blood urea nitrogen
- CCI
Charlson Comorbidity Index
- CI
Confidence interval
- CKRT
Continuous kidney replacement therapy
- OR
Odds ratio
- SOFA
Sequential Organ Failure Assessment
Author contributions
Conceptualization: HYJ. Methodology: SWL, YJS, and HYJ. Formal analysis: SWL, YJS, and HYJ. Investigation: SWL, JHL, JYC, JHC, SHP, CDK, YLK, and HYJ. Data curation: SWL and HYJ. Writing (original draft): SWL and HYJ. Writing (review and editing): HYJ. Approval of final manuscript: all authors.
Funding
None.
Data availability
The datasets used and analysed during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
The Institutional Review Board of Kyungpook National University Hospital reviewed and approved the study protocol (No. 2025-06-010). All clinical investigations were conducted in accordance with the guidelines of the 2008 Declaration of Helsinki. Informed consent was waived because all patients’ medical records and information were anonymized and unidentified before the analysis.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets used and analysed during the current study are available from the corresponding author on reasonable request.