Impact of Diabetes on COVID-19 Mortality and Hospital Outcomes, a Global Perspective: An ONTOP Systematic Review and Meta-Analysis

Background: To date, COVID-19 has claimed 4.9 million lives. Diabetes has been identified as an independent risk factor of serious outcomes in people with COVID-19 infection. Whether that holds true across world regions uniformly has not been previously assessed.Methods: This study offers the first ONTOP systematic review and meta-analysis to analyse the collective and geographically stratified mortality, ICU admission, ventilation requirement, illness severity and discharge rate among patients with diabetes. Five databases were searched from inception to 30 th of August 2021. Prospective and retrospective cohort studies, reporting the association between diabetes and one or more COVID-19 hospitalization outcomes, were included. This meta-analysis was registered on PROSPERO, CRD42021278579.Findings: Overall, 158 observational studies were included, with a total of 270212 of participants, median age 59 [53-65 IQR] of who 56.5 % were male. A total of 22 studies originated from EU, 90 from Far East, 16 from Middle East, and 30 from America. Data were synthesised with mixed heterogeneity across outcomes. Pooled results highlighted that patients with diabetes were at a higher risk of COVID-19-related mortality, OR 1.87 [95%CI 1.61, 2.17]. ICU admissions were increased across all studies for patients with diabetes, OR 1.59 [95%CI 1.15, 2.18], a result that was mainly skewed by Far East-originating studies, OR 1.94 [95%CI 1.51, 2.49]. Ventilation requirements were also increased amongst patients with diabetes worldwide, OR 1.44 [95%CI 1.20, 1.73] as well as their presentation with severe or critical condition, OR 2.88 [95%CI 2.29, 3.63]. HbA1C levels under < 70 mmol and metformin use constituted protective factors in view of COVID-19 mortality, while the inverse was true for concurrent insulin use.Interpretation: Whilst diabetes constitutes a poor prognosticator for various COVID-19 infection outcomes, variability across world regions is significant and may skew overall trends.Registration Details: This meta-analysis was registered on PROSPERO, CRD42021278579.Funding Information: No funding was received for the presented work.Declaration of Interests: The authors have no conflict of interest to declare.