We recruited 1619 consecutive admissions, with mean age 76.4 (7.9) years and 51.3% females. 112 (6.9%) patients had missing 30-day follow-up data. Complete case analysis was performed for 1507 patients, of whom 331 (22.0%) were re-admitted within 30-days of discharge. Depressive symptomatology was reported by 352 (21.8%) participants, while 44 (2.7%) participants had a history of established depression but were asymptomatic at time of admission. Malnutrition was prevalent in 13.4% participants at admission. Factors associated with 30-day readmission Table 1 compares the characteristics of patients with and without 30-day readmission. Patients with 30-day readmission were more likely to report depressive symptoms (26.1% vs 20.4%, P<0.001) compared with patients who were not readmitted. Malnutrition at admission was more prevalent among patients who were readmitted within 30-days compared with those without readmission (17.4% vs 11.6%, P<0.01). Patients who were readmitted within 30 days had significantly longer length of stay during the index admission compared with those who were not readmitted, with observed differences in patterns of admission diagnoses but not severity of illness. Patients with 30-day readmission had higher comorbidity burden, were more likely to have been admitted to hospital in the one-year preceding index admission, more often cognitively impaired and had more severe frailty at baseline. Delirium, functional decline and poor oral intake during the index admission were all significantly more commonly observed among patients who were readmitted within 30 days of discharge.
Table 1
Baseline and hospitalization characteristics for patients with and without 30-day readmission
Association of depressive symptoms and malnutrition with other geriatric syndromes
The presence of active depressive symptoms was significantly associated with frailty (CFS >5, OR=1.62, 95% CI 1.22-2.16, P=0.039), poor oral intake during hospitalization (OR=1.35, 95% CI 1.02-1.79, P=0.037), and inpatient functional decline (OR=1.58, 95% CI 1.11-2.23, P=0.011), when referenced against patients with neither depressive symptoms nor history of depression (Table 2). Prior depression diagnosis even in the absence of active depressive symptoms, as well as inability to communicate symptoms, were significantly associated with frailty, poor oral intake, functional decline, delirium and cognitive impairment. Malnutrition was significantly associated with all geriatric syndromes examined, with the exception of functional decline during hospitalization (P=0.076).
Table 2
Logistic regression for depressive symptoms and malnutrition with other geriatric syndromes
DAG-derived adjustment for the causal association of depressive symptoms and malnutrition with 30-day readmission
For the effect of depression on 30-day readmission with 15 co-variates, 29 causal paths were identified and the minimal adjustment set included age, comorbidity, gender, ethnicity, living alone and having an admission in the preceding one year (Fig. 1A). After adjusting for the confounding variables in the minimal adjustment set, patients reporting depressive symptoms had significantly increased risk for 30-day readmission (OR=1.38, 95% confidence interval 1.02-1.86, P=0.039) when referenced against patients with neither depressive symptoms nor history of depression (Table 3). Patients with an established depression diagnosis but not experiencing active depressive symptoms were not at risk for 30-day readmission. Patients who were unable to communicate their symptoms were also at increased risk for 30-day readmission (OR=2.11, 95% confidence interval 1.35-3.28, P=0.001). Positive depressive symptoms and inability to communicate depressive symptoms remained significant risk factors for 30-day readmission in multiple imputation and sensitivity analyses.
Table 3
Estimated odds ratios for depressive symptoms on 30-day readmission
The DAG for malnutrition on 30-day readmission included 14 causal paths and age, depression and ethnicity were identified as potential confounders in the minimal adjustment set (Fig. 1B). Malnutrition at admission was significantly associated with 30-day readmission in the unadjusted model (OR=1.59, 95% confidence interval 1.14-2.23, P=0.007). In the minimal adjustment set to account for confounding by age, ethnicity and depressive symptoms, malnutrition retained association with 30-day readmission, although no longer statistically significant (OR=1.40, 95% confidence interval 0.99-1.98, P=0.058) (Table 4). Malnutrition remained significantly associated with 30-day readmission in multiple imputation analysis (OR=1.48, 95% CI 1.08-2.02, P=0.014), and in sensitivity analyses for which all patients with missing 30-day follow up were assumed as having been readmitted (OR=1.46, 95% confidence interval 1.08-2.06-1.99, P=0.018). The association between malnutrition and 30-day readmission was no longer statistically significant (P=0.075) in sensitivity analyses that assumed missing follow-up data as not having been readmitted.
Table 4
Estimated odds ratios for malnutrition on 30-day readmission
Using the conventional approach of including all variables with univariate P<0.05 in their association with depressive symptomatology and 30-day readmission – comorbidity burden, admission diagnosis, previous hospitalization, frailty status, cognitive impairment, malnutrition, poor oral intake and functional decline during admission - alongside a priori adjustment for age, gender and ethnicity, depressive symptomatology was no longer associated with readmission risk, although patients who were unable to communicate symptoms remained at increased risk for 30-day readmission (Table 3). Comorbidity burden, previous hospitalization, frailty status, depressive symptomatology, cognitive impairment and poor oral intake during admission were associated with both malnutrition and 30-day readmission on univariate analyses. In multiple logistic regression with a priori adjustment for age, gender, ethnicity, and all significant univariate covariates, malnutrition was not associated with readmission risk (Table 4).