Background <p>Elevated blood sugar levels, including diabetes mellitus (DM) or hyperglycemia at the time of hospital admission, are key risk factors for adverse outcomes in COVID-19 patients.</p> Objective <p>The following study aims to establish a correlation between the glycemic gap, patients with pre-existing diabetes mellitus, and adverse outcomes from COVID-19. It also examines the correlation of biomarkers, such as D-dimer, serum ferritin, C-reactive protein (CRP), blood urea nitrogen (BUN), and serum creatinine, with disease severity.</p> Methods <p>In this prospective cohort study, 200 COVID-19 patients with pre-existing diabetes mellitus were included. Patients under the age of 18, those who presented with hypoglycemia on admission, diabetic ketoacidosis, or who were receiving corticosteroid treatment were excluded. The data were analyzed through descriptive and inferential statistical methods, which included numerical and categorical variables such as mean, standard deviation (S.D.), frequencies, and percentages. The data were analyzed to determine the relationship of variables.</p> Results <p>The present study found that an increased glycemic gap in patients is significantly associated with poor outcomes of COVID-19. Also, the study’s biomarkers D-dimer, serum ferritin, CRP, and BUN have been considerably correlated with disease severity.</p> Conclusion <p>These results contribute to the existing knowledge on the glycemic gap in COVID-19 outcomes and provide helpful insights into patient management and therapeutic approaches.</p>