Time in Range vs. HbA1C

If you have Diabetes, your visit to the Doctor has always had a blood test called an HbA1C linked to it. The number that we seem to think defines our diabetes management success!

An HbA1C test has been the main assessment tool we use to see if diabetes is well managed or uncontrolled and therefore showing a high risk for complications. The aim for most people is to maintain an HbA1C <7.0%. (This may differ based on your age and other factors, so check with your healthcare professional what your personal target is).

An HbA1C is an indication of your average blood sugar levels the past 3months . An HbA1C of <7.0% indicates that your average blood sugar levels that you measure daily range around <8.6mmol/L.

The challenge with an HbA1C is that it is exactly that: an average. This means it takes extremely high blood glucose levels and frequent hypoglycemic levels and evens them out to a nice looking average as an HbA1C.

Some limitations of an HbA1C test:

  • It shows no information about acute glycaemic excursions - episodes of very high or low blood sugar levels.

  • It fails to identify the frequency of intra- and interday glucose variations.

  • It’s result is impacted by the following: anamia, hemoglobinopathies, iron deficiency and pregnancy.

See the image to the left for a more visual explanation of some of the limitations of just using an HbA1C to assess diabetes. All three scenarios have an HbA1C result that looks healthy - on further assessment with tools such as Continuous Glucose Monitoring (CGM), we find daily levels that tell a different story:

Continuous glucose monitoring (CGM) systems have become more accessible to people in the past few years. CGM systems continually monitor glucose in the blood through an external device attached to the body that then give real-time updates via an app on your phone or a separate scanning device.

This allows people to immediately observe changes in their blood sugar levels and allows them to then make immediate treatment or lifestyle changes based on what they see. It also allows people to see patterns in their blood sugar levels of hypo- and hyperglycemia and make the appropriate changes.

The three CGM systems currently available in South Africa are:

  • Abbott Freestyle Libre Flash Glucose Monitoring System

  • Dexcom G6

  • Medtronic Guardian 4

CGM Limitations:

  • It needs to be actively used in order to be effective.

  • It can induce anxiety in some people.

  • Can have accuracy limitations when your sugar levels are changing rapidly as it monitors changes in interstitial fluid which is delayed by a few minutes to blood sugar levels.

Interpreting all the extra information we get to see from CGM is important. We don’t want to have access to all this information and insight and do nothing with it!

This has lead to a new range of targets for analyzing CGM data:





TIR is the percentage of the time that a person spends with their blood sugar levels in a target range. The target range will differ sometimes so it is always good to check yours with your healthcare provider, but generally guidelines suggest a range of 3.9 - 10mmol/L.

Each range has specific targets based on categories of people living with diabetes.

Below are the recommended ranges based on specific categories:

If you are using a CGM system, find the category you fall into and discuss your Time In Range target with you health care professionals.

Use the data to see how food and exercise influence sugar levels as well as stress or sickness or changes in your daily routines.

Discuss your CGM download with your healthcare team and look at patterns and identify adjustments to be made and goals to be set. The data from your CGM should be used together with you HbA1C to provide a more comprehensive picture.

In conclusion, it is not about using only an HbA1C result, or only your CGM download data to assess your diabetes health, but rather the complimentary benefit of using them both together!

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