Hip fractures in the elderly present a major global health concern (1). With population aging, the incidence is projected to surpass 4.5 million cases per year by 2050 (2). These fractures often occur due to falls and osteoporosis, frequently requiring surgical treatment to enable earlier rehabilitation and improved outcomes compared to conservative management (3, 4). However, surgery also carries risks of complications like infections, deep vein thrombosis, pulmonary embolism, and readmission (5, 6).

30-day readmission rates within 30 days of discharge following hip fracture surgery range from 4% to 30% (7, 8). Readmissions lead to more severe complications, extended recovery times, increased costs, and poorer outcomes (7–9). Current research has mainly focused on the effects of complications, malnutrition and frailty status on readmissions, with less attention to the influence of metabolic disorders on early readmission after hip fracture surgery in the elderly (8, 9).

Admission hyperglycemia, defined as blood glucose ≥6.1 mmol/L upon hospital admission, is a common metabolic disorder among geriatric hip fracture patients (10, 11). In most cases, admission hyperglycemia reflects stress-induced hyperglycemia resulting from the physiological trauma response (12). Specifically, the stress of the fracture initiates hormonal changes, including elevated cortisol and catecholamines, which lead to increased hepatic glucose production and reduced insulin sensitivity, contributing to high blood glucose levels (13, 14). Prolonged stress-induced hyperglycemia can impair immune function, delay wound healing, and increase infection risk (15, 16). These factors may coexist, negatively impacting 30-day readmission rates after hip fracture surgery in geriatric patients.

However, the association between admission hyperglycemia and 30-day readmission after hip fracture surgery remains unclear. Elucidating this relationship is crucial to identifying modifiable factors to reduce readmissions. Therefore, this study aimed to investigate the correlation between admission hyperglycemia and 30-day readmission after hip fracture surgery in geriatric patients using propensity score matching analysis. The Findings from this study may provide evidence to recommend routine blood glucose testing upon admission and perioperative glycemic control to improve outcomes in this vulnerable population.

In this study, we found that admission hyperglycemia was independently associated with an increased risk of 30-day hospital readmission after hip fracture surgery in geriatric patients. The dose-response relationship observed between elevated glucose levels and higher readmission risk further corroborates hyperglycemia as a prognostic factor.

Notably, the association between admission hyperglycemia and readmission remained significant even after adjusting for potential demographic and clinical confounders. This indicates that hyperglycemia itself contributes to poorer short-term outcomes, rather than merely serving as a marker of greater comorbidity burden. Propensity score matching also yielded consistent results, confirming that the hyperglycemia-readmission link cannot be fully attributed to baseline differences between the groups.

Our analysis produced consistent conclusions with already published studies exploring similar hypotheses. For example, Evans et al. found that patients with high blood glucose levels (>6.5 mmol/l) upon hospital admission tended to have greater 28-day mortality rates and higher readmission frequencies in a retrospective cohort study of 1,502 patients (17). In addition, Farrugia et al. indicated admission glucose remained a significant predictor of 1-year readmission (18). Zhou et al. established the stress hyperglycemia ratio impacts the rehospitalization rate in patients with acute decompensated heart failure and diabetes (HR 1.54 [95% CI 1.03-2.32]) (19). Martin et al. conducted a study of 3,109 patients admitted to the intensive care unit and confirmed serum glucose can predict ICU readmission (20). Murphy et al. investigated 258 patients with burn injury and found patients with hyperglycemia had considerably longer hospitalizations (13 vs 9 days; P = 0.038) and greater rates of unscheduled rehospitalizations (18.8 vs 3.6%; P =0.001) compared to the control group (21).

Several mechanisms may underlie the observed relationship between hyperglycemia and increased readmission. Firstly, acute hyperglycemia can directly impair immune cell function, wound healing, and vascular epithelial integrity through advanced glycation end-products and oxidative stress (15, 16, 22–24). This may increase susceptibility to postoperative complications like surgical site infections, delirium and postoperative pneumonia, necessitating readmission. For example, Tang et al. analyzed 600 geriatric patients with hip fractures and revealed admission hyperglycemia in elderly hip fracture patients increases the risk of postoperative pneumonia more than those with normal glucose levels (OR = 2.090, 95% CI: 1.135-3.846, p = 0.016) (25). Anderson et al. demonstrated patients with blood glucose levels of 200 mg/dL or higher upon hospital admission were significantly more likely to develop deep surgical site infections in orthopaedic trauma patients (26). Windmann observed hyperglycemia was significantly associated with postoperative delirium in a prospective observational study. (OR 3.86 [CI 95% 1.13, 39.49], P=0.044) (27).

Secondly, admission hyperglycemia may be indicative of undiagnosed diabetes or poor long-term glycemic control in known diabetic patients. Sustained hyperglycemia can promote endothelial dysfunction and microvascular damage through mechanisms like advanced glycation end-product accumulation and protein kinase C activation (28–31). This macro- and microvascular dysfunction can exacerbate tissue hypoxia and ischemic injury, worsening prognosis.

Lastly, hyperglycemia induces a prothrombotic state by increasing platelet aggregation, plaque rupture risk, and impairing fibrinolysis (32, 33). Hypercoagulability coupled with endothelial injury significantly increases the risk of thromboembolic events like deep vein thrombosis and pulmonary embolism after major orthopedic surgery (34). For example, Yao et al. analyzed 217 patients with femoral neck fractures and found patients with admission hyperglycemia demonstrate a higher incidence of developing deep vein thrombosis (OR 3.03, 95% CI 0.77-11.87) (34).

Interestingly, the association between admission glucose and 30-day readmission differed between diabetics and non-diabetics in this study. The inflexion point for increased readmission odds was lower for non-diabetics compared to diabetics (5.80 mmol/L for the non-diabetic group and 8.70 mmol/L for the diabetes group). This corroborates that acute stress-induced hyperglycemia poses a greater risk in non-diabetics. In contrast, chronically elevated glucose in diabetics exerts a more gradual dose-dependent effect on outcomes. Bellis found that outcomes for patients with stress-induced hyperglycemia are worse than for patients with hyperglycemia who have diabetes in a study of acute coronary syndrome (35). Prospective studies are needed to clarify the causal relationships and mechanisms.

The interactions between admission hyperglycemia and hypoalbuminemia/renal dysfunction suggest these comorbidities exacerbate hyperglycemia’s effects. The interaction with hypoalbuminemia, indicating malnutrition, may exacerbate hyperglycemia’s deleterious effects (36, 37). Malnutrition impairs immunity and wound healing, while hyperglycemia induces glucotoxicity and oxidative stress. Their synergistic adverse effects on recovery may partly explain higher readmission rates when both factors are present. Additionally, the interaction between hyperglycemia and elevated blood urea nitrogen, indicating renal dysfunction, may amplify hyperglycemia’s impact. Nephropathy can reduce drug clearance and cause fluid/electrolyte imbalances, compounding hyperglycemia’s risks (38, 39). This interplay may increase readmission likelihood when both factors occur. In addition, relevant literature indicates that analyzing multiple subgroups may lead to false positive findings (40).

The significant interactions found between admission hyperglycemia and serum albumin as well as blood urea nitrogen warrant further discussion. Prospective studies examining their combined versus isolated impacts are needed to clarify the causal relationships and mechanisms. A better understanding of these synergistic risks will inform the management of complex patients.

Cardiovascular disease is highly prevalent in elderly hip fracture patients and an important contributor to postoperative complications and mortality. Conditions like coronary artery disease, heart failure, arrhythmias, broken heart syndrome and Takotsubo cardiomyopathy can exacerbate tissue hypoxia, limit mobility, and predispose patients to thromboembolic events, delirium and cardiac complications after major surgery (41). Acute hyperglycemia further amplifies cardiovascular risk through mechanisms like sympathoadrenal activation, oxidative stress, inflammation, and hypercoagulability (32). The synergistic adverse effects of cardiovascular disease and hyperglycemia on recovery likely contribute to higher 30-day readmission rates when both factors coexist in hip fracture patients. Managing cardiovascular comorbidities through beta blockers, statins and anticoagulation while controlling hyperglycemia may help attenuate readmissions. Future studies should examine whether optimizing cardiovascular status and glycemic control in the perioperative period improves outcomes compared to routine care.

This study has several strengths. The sample size was adequately powered to detect significant associations between hyperglycemia status and 30-day readmission. Confounding was rigorously accounted for through multivariate regression and propensity score matching. The dose-response relationship analysis visualized the relationship between admission hyperglycemia and 30-day readmission. Several limitations should also be acknowledged. The single-center retrospective design precludes establishing causality. Further prospective studies are needed to confirm these findings in other cohorts and determine causative treatments. Data was lacking on medications, surgical complications beyond 30 days, and causes for readmission. Residual confounding from unmeasured factors may still exist despite adjustment. Additionally, while this study suggests potential interventions like routine glucose testing and perioperative glycemic control, the lack of a cost-effectiveness analysis of these strategies limits the practical applicability and clinical recommendations. Future studies should investigate the cost-effectiveness of intensive perioperative glucose management protocols compared to routine care.

In conclusion, this study provides evidence that admission hyperglycemia independently predicts increased 30-day readmission risk after hip fracture surgery in the elderly. Routine glucose testing upon admission and perioperative glycemic control through insulin protocols may help attenuate short-term readmissions. Our findings warrant future longitudinal studies to define optimal glycemic targets across the perioperative period. A cost-effectiveness analysis of intensive glucose management strategies is also needed. Ultimately, an evidence-based approach incorporating admission glucose status into risk stratification models could help improve the quality of care and outcomes for this vulnerable patient population.

All the data used and analyzed during the current study are available from the corresponding author upon reasonable request.

The studies involving humans were approved by the Ethics Committee of Dandong Central Hospital (No. DDZX-202211013). The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation was not required from the participants or the participants’ legal guardians/next of kin in accordance with the national legislation and institutional requirements.

RH: Conceptualization, Investigation, Writing – review & editing. WT: Data curation, Supervision, Writing – original draft. XN: Conceptualization, Investigation, Writing – original draft. WY: Conceptualization, Investigation, Writing – original draft. WW: Methodology, Writing – original draft. QL: Project administration, Writing – original draft. WD: Project administration, Writing – original draft.