Time in Range Theory

Researchers globally have been reviewing the ‘time in range’ theory as a more accurate predictor of future possible complications from Type 1 Diabetes. This coupled with Continuous Glucose Monitors (CGM) make the monitoring of the time in range so much easier for those diagnosed.

In 2017 in the United States, leading diabetes organisations issued a concensus statement defining health outcomes beyond HbA1c. The following sections have been taken from the study:

An individual whose blood glucose levels rarely extend beyond the thresholds defined for hypo- and hyperglycemia is less likely to be subject to the short-term or long-term effects experienced by those with frequent excursions beyond one or both thresholds. It is also evident that if the intent of a given intervention is to safely manage blood glucose but the intervention does not reliably maintain blood glucose within safe levels, then the intervention should not be considered effective.

The time in range outcome is distinguished from traditional HbA1c testing in several ways. Time in range captures fluctuations in glucose levels continuously, whereas HbA1ctesting is done at static points in time, usually months apart. Furthermore, time in range is more specific and sensitive than traditional HbA1c testing; for example, a treatment that addresses acute instances of hypo- or hyperglycemia may be detected in a time in range assessment but not necessarily in an HbA1c assessment. As a percentage, time in range is also more likely to be comparable across patients than HbA1c values, which are more likely to have patient-specific variations in significance. Finally, time in range may be more likely than HbA1c levels to correlate with PROs, such as quality of life, because the outcome is more representative of the whole patient experience. 

At least one study has demonstrated the direct clinical relevance of time in range correlating to positive overall outcomes. This prospective inpatient study evaluated 227 patients (100 with type 2 diabetes and 127 without diabetes) post–cardiac surgery to assess glucose control. For the purposes of this study, time in range was defined as being time in the range of 108–146 mg/dL (6.0–8.1 mmol/L). Patients received insulin to target glucose concentrations within that range. The results of the study showed that post–cardiac surgery patients with 80% of time within a range of 108–146 mg/dL (6.0–8.1 mmol/L) had better outcomes, with or without diabetes, compared with patients with less than 80%. While the factors influencing inpatient recovery are varied, the study suggests a correlation between positive outcomes and time in range. Other research has indicated a link between a high percentage of time in range with recovery of glucose counterregulation and hypoglycemia symptom recognition in patients with type 1 diabetes following intrahepatic islet transplantation.

More commonly, time in range has been adopted by researchers evaluating the precision and effectiveness of emerging glucose monitoring and automated insulin delivery technologies. None of these studies relate time in range to any long-term diabetes outcomes, as these studies are of short duration. In one example, researchers compared a wearable, bihormonal, automated device to an insulin pump for 5 days over a 96-h period in 52 adults and adolescents with type 1 diabetes. Researchers measured the percent time in range by the hour, and the desired glucose range was defined as 70–180 mg/dL (3.9–10.0 mmol/L). They demonstrated that the bihormonal device was able to keep patients within a range of 70–180 mg/dL (3.9–10.0 mmol/L) for more time than the insulin pump, concluding that this device was a more effective means of managing blood glucose.



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