Diabetes Mellitus and In-Hospital Outcomes in Hospitalized COVID-19 Patients: A Single-Center Eastern European Cohort Study (2020–2024)

<i>Background and Objectives</i>: Diabetes mellitus (DM) has been consistently linked to severe coronavirus disease 2019 (COVID-19) and adverse outcomes; however, the extent to which DM independently predicts mortality and cardiovascular complications in real-world hospitalized cohorts remains debated, particularly in Eastern Europe. This study aimed to evaluate the impact of DM on cardiovascular complications and in-hospital outcomes among adults hospitalized with SARS-CoV-2 infection. <i>Materials and Methods</i>: We conducted a single-center retrospective observational cohort study including consecutive adult patients hospitalized with laboratory-confirmed SARS-CoV-2 infection between March 2020 and December 2024 at the "Victor Babeș" Clinical Hospital of Infectious Diseases and Pneumophthisiology, Timișoara, Romania. DM status (type 1, type 2, or newly diagnosed diabetes) was defined using structured dataset fields. The primary outcome was in-hospital all-cause mortality. Secondary outcomes included ICU admission, length of stay, pulmonary embolism (PE) on CT pulmonary angiography (CTPA), and a composite of in-hospital cardiovascular/thromboembolic complications. Multivariable logistic regression models adjusted for clinically relevant covariates (age, sex, BMI, vaccination status, hypertension, ischemic heart disease, atrial fibrillation, prior ischemic stroke, and admission creatinine). <i>Results</i>: A total of 395 patients were included; 98 (24.8%) had DM. Diabetic patients exhibited a high cardiometabolic burden (arterial hypertension: 83.7% vs. 77.4%, <i>p</i> = 0.242) and higher admission renal markers (urea: 55.6 [41.0-79.1] vs. 48.6 [39.2-68.0] mg/dL, <i>p</i> = 0.047; creatinine: 1.04 [0.76-1.52] vs. 0.88 [0.59-1.33] mg/dL, <i>p</i> = 0.008). In-hospital mortality was numerically higher in DM (9.2% vs. 6.7%, <i>p</i> = 0.560), as was ICU admission (7.1% vs. 4.7%, <i>p</i> = 0.503), without statistical significance. PE on CTPA occurred in 13.3% of DM vs. 11.4% of non-DM patients (<i>p</i> = 0.763). In univariable analysis, DM was not significantly associated with mortality (OR 1.40, 95% CI 0.62-3.19; <i>p</i> = 0.422) or ICU admission (OR 1.55, 95% CI 0.61-3.97; <i>p</i> = 0.356). After multivariable adjustment, DM remained not independently associated with mortality (adjusted OR 1.09, 95% CI 0.42-2.83; <i>p</i> = 0.854) or ICU admission (adjusted OR 1.19, 95% CI 0.42-3.36; <i>p</i> = 0.747). <i>Conclusions</i>: In this real-world Eastern European cohort of hospitalized adults with SARS-CoV-2 infection, diabetes mellitus was common and associated with significantly worse renal function at admission, but it was not statistically associated with in-hospital mortality or ICU admission after multivariable adjustment; however, the limited number of events and low events-per-variable raise concerns about model stability and potential false-negative findings. These findings support a risk-marker model in which adverse COVID-19 outcomes in diabetic patients are driven primarily by clustered vulnerability and organ dysfunction rather than diabetes status alone.