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Does COVID-19 Cause New-Onset Diabetes or Unmask Pre-Existing Diabetes?

Background: Many cases of newly diagnosed diabetes were reported in association with coronavirus 2019 (COVID-19) caused by the severe acute respiratory syndrome-associated coronavirus-2 (SARS-CoV-2). Objective: To clarify whether COVID-19 triggers new diabetes or unmask pre-existing undiagnosed diabetes. Methods: PubMed search of literature up to February 3, 2021. Search terms included diabetes, COVID-19, diagnosis, hemoglobin A1c (HbA1c), diabetic ketoacidosis, diabetes ketoacidosis, pancreatitis. Case reports, case series, retrospective studies, reviews, and pertinent in-vitro investigations were reviewed. Results: Retrospective studies and case series suggest that COVID-19 can worsen diabetes control and precipitate hyperglycemic crises in patients admitted to the hospital. Majority of these patients had pre-existing undiagnosed type 2 diabetes as reflected by elevated HbA1c levels on admission. Many patients presenting with hyperglycemia and normal HbA1c levels may have transient stress hyperglycemia. This group of patients are misclassified as new-onset diabetes despite lack of patient follow-up after discharge. Only one case report of possible new-onset diabetes described a patient with pre-diabetes who progressed to severe diabetes 6 weeks following COVID-19 pneumonia. Mechanisms of worsening glycemic control by COVID-19 infection include increased release of cytokines and insulin counter-regulatory hormones. Binding of SARS-CoV-2 to pancreatic β-cells and their subsequent destruction by the virus as another mechanism requires further studies. Conclusion: COVID-19 infection commonly unmasks pre-existing diabetes. Follow-up of patients presenting with new-onset hyperglycemia after hospital discharge is essential to distinguish between stress hyperglycemia and new-onset diabetes.