Hemoglobin A1c (HbA1c or A1c for short) is the most commonly used blood test to measure blood sugar levels for people with diabetes. High HbA1c levels are linked to serious long-term complications for people living with all types of diabetes. In a recent study of 7,337 patients with COVID-19, 952 people had type 2 diabetes. Researchers found that even a 0.8% difference in A1c level made a big difference in their COVID-related health outcomes. One group had A1c levels above a healthy range. This poorly controlled group did much worse than the well-controlled group with a lower average A1c. Compared to well-controlled groups, poorly controlled groups had higher rates of in-hospital death (1.1% vs 11%, respectively) and heart injury (1.4% vs 9.9%). Poorly controlled groups also had higher rates of other serious complications. High blood sugar levels impair the immune system, putting people at greater risk from any infection. Patients with diabetes are more likely to experience worse outcomes if they develop COVID-19. This study demonstrates what others have shown in the past: that even small improvements in blood sugar can significantly reduce diabetes-related risk.