In the latter part of 2019, a cluster of unexplained pneumonia cases were reported in Wuhan, China. In less than a year, SARS-CoV-2 has infected over 27 million people and claimed more than 800,000 deaths worldwide. Diabetes is a highly prevalent chronic metabolic disease, and recent reports have suggested a possible existence of COVID-19 related new-onset diabetes. Hyperglycemia induces an inflammatory state in the body, which coupled with coronavirus associated immune response is a possible explanation for clinical worsening of patients. We present a summary and pooled analysis of available evidence to ascertain the relationship between hyperglycemia in undiagnosed diabetics and outcomes of COVID-19 disease. Our results showed that hyperglycemia in non-diabetics was associated with higher risk of severe/critical illness (OR 1.837 (95% CI 1.368-2.465, P < 0.001) and mortality (2.822, 95% CI 1.587-5.019, P < 0.001) compared with those with normal values of blood glucose. The management of hyperglycemia in COVID-19 poses significant challenges in clinical practice, and the need to develop strategies for optimal glucose control in these patients cannot be overlooked.