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SIGN decision support

Glucose metrics

Optimising glycaemic control in people with type 1 diabetes (SIGN 170)
Healthcare Improvement Scotland

Use the Ambulatory Glucose Profile (AGP) to guide glycaemic management

 

Applies to adults, children, and young people

The AGP may be used to guide glycaemic management of people with diabetes. Assessment should be based on a number of further measures, for example Glucose Management Indicator (GMI), Time in Range (TIR), frequency of severe hypoglycaemia.

 

 

 

 

Applies to adults, children, and young people

When using the AGP, a systematic approach to interpreting CGM data is recommended:

  1. Review the overall glycaemic status (eg, GMI, average glucose)
  2. Check Time Below Range (TBR), TIR, and Time Above Range (TAR) statistics, focusing on hypoglycaemia (TBR) first. If the TBR statistics are above the cutpoint for the clinical scenario (ie, for most people with type 1 diabetes >4% <3.9 mmol/L; >1% <3.0 mmol/L), the visit should focus on this issue. Otherwise, move on to the TIR and TAR statistics.
  3. Review the 24-hour glucose profile to identify the time(s) and magnitude(s) of the problem identified.
  4. Review treatment regimen and adjust as needed.

 

 

 

 

Applies to adults, children, and young people

The two metrics, %TIR and %TBR, should be used as a starting point for the assessment of glycaemic control and as the basis for therapy and lifestyle adjustment. Particular emphasis on reducing %TBR is warranted when the percentages of CGM values falling below 3.0 mmol/L or 3.9 mmol/L are close to or exceed targets.

 

 

 

Applies to adults, children, and young people

Continuous glucose monitoring metrics derived from continuous glucose monitor use over the most recent 14 days (or longer for patients with more glycaemic variability), including time in range (3.9–10 mmol/L), time below target (<3.9 mmol/L and <3.0 mmol/L), and time above target (>10 mmol/L), are recommended to be used in conjunction with HbA1c whenever possible.

 

 

 

 

Ambulatory Glucose Profile (AGP) is a report summarising CGM data over multiple days of wear and is available from all CGM devices and the linked reporting tools. These reports allow a standardised summary of key information consisting of some or all of the following: data completeness, glucose level statistics (eg, hypoglycaemia, hyperglycaemia and TIR), glucose profile based on a “summary day” (also named the AGP), glucose management indicator (GMI) and daily glucose profiles.

A UK Best Practice Guide on Glucose Metrics can be found at Time in range: A best practice guide for UK diabetes healthcare professionals in the context of the COVID‐19 global pandemic. We support the guidance that ‘%TIR should be used in conjunction with AGP data for a fuller picture of glycaemic health and as a basis for managing therapy and making treatment decisions’. It is important that clinicians appreciate that %TIR is not a surrogate for HbA1c and has a clinical utility that is different from HbA1c, since %TIR reflects the combined influence of glucose exposure and the degree of glycaemic variability.

 

Time in ranges: targets for people with type 1 diabetes.
Time in ranges: targets for people with type 1 diabetes. TAR, time above range; TIR, time in range

Source: Wilmot EG, Lumb A, Hammond P, Murphy HR, Scott E, Gibb FW, et al. Time in range: A best practice guide for UK diabetes healthcare professionals in the context of the COVID-19 global pandemic. Diabet Med. 2021 Jan;38(1):e14433. https://doi.org/10.1111/dme.14433

 

The review of AGP data in the clinic should be guided by the issues brought to the consultation by the person with diabetes as these will need to be dealt with before they will be ready to discuss the AGP.

 

HbA1c measurement and targets

 

Applies to adults

Measure HbA1c every 3-6 months in adults with type 1 diabetes who are not using CGM technologies that can estimate HbA1c.

Measure HbA1c at least every 12 months in adults with type 1 diabetes who are using CGM technologies that can estimate HbA1c.

 

 

 

Applies to children and young people

Measure HbA1c every 3-6 months in children and young people with type 1 diabetes who are not using CGM technologies that can estimate HbA1c.

Measure HbA1c at least every 12 months in children and young people with type 1 diabetes who are using CGM technologies that can estimate HbA1c.

 

 

 

Applies to adults

Agree an individualised HbA1c target with each adult with type 1 diabetes. Take into account factors such as their daily activities, aspirations, likelihood of complications, comorbidities, occupation and history of hypoglycaemia.

 

 

 

Applies to children and young people

Agree an individualised lowest achievable HbA1c target with each child or young person with type 1 diabetes and their families or carers. Take into account factors such as their daily activities, individual life goals, complications, comorbidities and the risk of hypoglycaemia.

 

 

 

Regular monitoring of HbA1c can help individuals optimise their glycaemic control, however, with the increasing use of CGM there is less need for laboratory HbA1c testing. As is highlighted in the ambulatory glucose profile recommendations, Glucose Management Indicator can provide a reasonable estimate of overall glucose control over a short period (5 days to 3 months) of time and can be used as an effective alternate biomarker for assessment of glucose exposure.

It is important to support a holistic approach to agreeing individualised HbA1c targets. In some instances a tighter control of HbA1c may be desirable such as when planning pregnancy or while pregnant. In other instances it may be more appropriate to set a higher HbA1c, particularly if there are concerns around hypoglycaemia or other factors such as frailty.  Clinicians should also be mindful that fixed HbA1c targets for the whole population (eg <53 mmol/mol) may be unrealistic for many people and become unhelpful as they set the individual to fail.

It is also worth noting that although HbA1c is a more abstract and hard‐to‐visualise measure of individual glycaemic control, it remains the gold standard for understanding population‐based risks for developing macrovascular and microvascular complications.

 

Applies to adults

Ensure that aiming for an HbA1c target is not accompanied by problematic hypoglycaemia in adults with type 1 diabetes.

 

 

 

Ensuring individuals have access to structured education is important as it has been shown to help to protect from hypoglycaemia whilst optimising glycaemic control. There is evidence that real-time CGM reduces hypoglycaemia with or without adjunctive use of insulin pump compared with intermittently-scanned CGM with or without use of an insulin pump.