Understanding GMI in Gludiary

What GMI Is and How It Is Calculated

GMI stands for Glucose Management Indicator, a measure introduced by a 2018 study led by Dr. Richard Bergenstal that converts an average glucose value into a percentage on the same scale as A1C (also written HbA1c), the lab measure that reflects your average blood glucose over roughly the past two to three months. GMI was developed to give people who log glucose frequently a same-scale approximation of A1C between lab tests, without a blood draw.

The published formula is GMI (%) = 3.31 + 0.02392 × average glucose (mg/dL). If you log in mmol/L, multiply your average by 18 to get mg/dL first, then apply the same formula. Gludiary applies this formula to the average of the readings you have logged. For example, an average of about 154 mg/dL produces a GMI of roughly 7.0%, and an average near 126 mg/dL produces a GMI of roughly 6.3%. Because it is built from your own log, your GMI updates as you add readings.

When GMI Can Mislead

The honest limitation of any GMI is that it is only as representative as the readings behind it. GMI was validated using continuous glucose monitor data, but a fingerstick log captures individual moments rather than continuous 24-hour glucose. That means the number can be skewed in several ways:

• Too few readings: an average built from only a handful of entries is not reliable.
• Biased timing: if you mostly test when you expect a good number (or a bad one), your average, and your GMI, leans that way.
• Missing highs or lows: readings you never take cannot be averaged in, so overnight or post-meal excursions may be invisible.

There are also medical reasons a lab A1C itself can differ from average glucose: certain anaemias, haemoglobin variants, pregnancy, recent transfusions and kidney disease among them, and GMI can diverge from a lab A1C for those same reasons, plus the inherent gap between fingerstick sampling and continuous monitoring. The takeaway is not to distrust the number, but to read it as a rough, moving indicator that is most useful when your logging is frequent and even-handed across the day.

It Does Not Replace a Lab A1C Test

This is the point that matters most, so it is worth stating plainly: Gludiary's GMI is an estimate and does not replace a laboratory A1C test ordered by your doctor. The lab test is the standard your care team relies on for diagnosis and for tracking long-term control, and no app calculation should be used in its place.

So what is GMI good for? It is a helpful, motivating indicator between lab tests, a way to see roughly where your logged average sits and whether it is trending in the direction you and your doctor want. Think of it as a companion to your appointments, not a substitute for them. When you get a lab result, comparing it with your in-app GMI can even tell you something useful: a large gap may mean your logging is not capturing your full glucose picture. General A1C targets exist (many adults aim for under 7%, but individual goals differ and some are higher or lower), and your personal target is set by your doctor.

This guide is for general information only and is not medical advice. Rely on your laboratory A1C and your doctor's guidance for diagnosis, targets and treatment decisions.