Switching from intermittently scanned continuous glucose monitoring (isCGM) to real-time continuous glucose monitoring (rtCGM) led to more time in range and fewer episodes of severe hypoglycemia, an industry-funded trial of Belgian patients with type 1 diabetes found. The unblinded study included 254 adult patients who had used isCGM for at least six months. Half switched to a rtCGM system for six months. The primary outcome, time with blood glucose levels between 3.9 and 10.0 mmol/L (70 to 180 mg/dL), was significantly higher with rtCGM (59.6% vs. 51.9%).
In patients with type 1 diabetes who were already familiar with isCGM, the ALERTT1 trial showed that the more complete information provided by rtCGM technology improved glycemic control and reduced time in clinically significant hypoglycemia compared with isCGM. rtCGM had additional continuous data updated every 5 minutes and alarms that likely led to the improved outcomes.
Although enhanced rtCGM data did not improve HbA1c by much, the increase in time in range led to approximately 99 more min/d in range. The magnitude of this improvement in glycemic control is, however, small and may not be expected to affect risks for diabetes complications. Similarly, the reduced time in hypoglycemia translated to only about 5 fewer min/d. How much this would affect a given patient is unknown, but it was accompanied by reduced worry. The reduction in severe hypoglycemia is perhaps the most gratifying result and seems to support the benefit of alarms as any reduction in this outcome is an opportunity to avoid immediate catastrophe.
Given that the study population started with relatively good HbA1c control (7.4%) and time in hypoglycemia was already at or near goals, there was little room for improvement. The incremental improvement with rtCGM vs. isCGM in patients who are naive to technology, have worse initial glycemic control, or have more frequent hypoglycemia is uncertain. The initial improvements in glycemic control and hypoglycemia from either technology would be of greater benefit than the incremental difference of rtCGM over isCGM.
Clinicians can use these results to reassure patients that good glycemic control can be achieved with either device. A deciding factor for choosing rtCGM over isCGM may be reduced severe hypoglycemia, best offered to patients who have excessive hypoglycemia, continue to have severe hypoglycemia despite using isCGM, or are at greater risk for hypoglycemia unawareness and serious consequences.
The trial results are timely but may become less applicable as isCGM devices are being updated to include alerts, which is a key feature for protection from severe hypoglycemia. Further research comparing rtCGM with updated isCGM technology is needed to inform future clinical decision making.