Association Between Long-Term Glycemic Control and Clinical Outcomes in Patients With Diabetes Mellitus Hospitalized for Lower Respiratory Tract Infections: A Retrospective Cohort Study.

Abstract

Introduction: Diabetes mellitus (DM) increases susceptibility to lower respiratory tract infections (LRTIs) and is associated with higher rates of complications and mortality. Although poor glycemic control is known to increase infection risk, it is unclear whether long-term glycemic status influences outcomes once an LRTI occurs. This study examined whether hemoglobin A1c (HbA1c) predicts clinical outcomes in adults with DM hospitalized for LRTI.

Methods: This retrospective, single-center observational study was conducted at Kantonsspital Baselland, Switzerland, and included adult patients with Type 1 and Type 2 DM hospitalized for LRTI between January 2023 and December 2024. Data were extracted from the hospital's electronic medical records system. Long-term glycemic control was assessed by HbA1c values. Outcomes included length of hospital stay (LOHS), readmission, and mortality at 30 and 180 days. Associations were evaluated using multivariable regression models adjusted for age, sex, and number of chronic comorbidities.

Results: A total of 389 patients were included, with a median age of 79 years (IQR 72-84) and 41.1% female. Multimorbidity was highly prevalent, with 76.9% of patients having ≥ 5 chronic conditions. The median HbA1c was 7.2%. The most frequent LRTI admission diagnosis was pneumonia (53.5%), followed by COVID-19 (25.2%) and COPD exacerbation (17.0%). The median LOHS was 8 days (IQR 5-12). Mortality was 5.7% in hospital, 7.5% at 30 days, and 18.2% at 180 days after admission. Rehospitalization occurred in 13.4% of patients within 30 days and 36.7% within 180 days after discharge. Higher HbA1c was modestly associated with longer LOHS (IRR 1.058, p = 0.004) but not with readmission or mortality at any time point.

Conclusion: Patients with DM hospitalized for LRTI are typically elderly, multimorbid, and experience high readmission and mortality rates. Long-term glycemic control showed an association with slightly prolonged hospital stay but no association with mortality or readmission. These findings indicate limited prognostic value of HbA1c in the acute LRTI setting and highlight the dominant role of age, sex, and multimorbidity. These findings are primarily applicable to frail, elderly patients with multimorbidity and should be interpreted cautiously in other populations. Prospective studies should investigate the impact of short-term glycemic control and structured inpatient diabetes management on outcomes.