How Do I Read an AGP Report From My CGM?

An AGP (ambulatory glucose profile) report takes every day your CGM recorded and collapses them onto one 24-hour clock. The middle line is your median glucose at each time of day; the dark band around it holds the middle half of your readings at that time and the light band holds 90% of them. Read it by looking for where the line rises and where the bands widen, then check time in range, GMI and variability for the summary numbers.

How do I read an AGP report from my CGM?

Start at the left edge, midnight, and move right. You are not looking at one day; you are looking at how several days overlapped.

• The solid middle line is your median. At each time of day, half your sensor readings were above it and half below it.
• The dark band around it is your 25th to 75th percentile. It holds the middle half of your readings at that time.
• The light band is your 5th to 95th percentile. It holds 90% of your readings, excluding the rare extremes.
• A narrow band at a time of day means your readings were similar; a wide band means they were not.

The common mistake is to read the light band as the whole range. It excludes the extreme 5% on each side.

The median tells you what your body usually does. The bands tell you how confident you should be in that median.

The median line: why it is not an average day

The median is a 50th percentile, not a mean. If one night the sensor reads 40 for 20 minutes because you slept on it, a mean at that hour would move. The median barely moves, because it just picks the middle sorted value. That is why AGP reports are built on percentiles rather than averages.

In practice, look at the time the median starts to rise after a meal. If breakfast is at 08:00 and the median peaks at 08:40, that is a typical post-meal peak. If the median does not peak until 09:30 or later, that is a slow rise. If it starts up at 08:05 and is already high by 08:15, that meal hits quickly. Peak height is still information, but a repeatable pattern is more actionable than a one-off peak. Note whether the bands around the peak are tight or wide.

The dark and light bands: your day-to-day consistency

The two bands answer the follow-up question people often skip: is this pattern stable?

• Dark band, 25th to 75th percentile: half of your readings at this time sit inside this band.
• Light band, 5th to 95th percentile: 90% of your readings at this time sit inside this band.
• Outside the light band: the 10% most extreme readings. These may be real or sensor artifacts.

A wide light band at 16:00 but a narrow one at 08:00 suggests your afternoons vary more than your mornings. That can come from different snack timing, stress, training or sleep. The AGP itself will not tell you why; it just tells you where to ask the question.

What is a normal time in range without diabetes?

Time in range on a standard AGP usually means the percentage of readings between 70 and 180 mg/dL (3.9 to 10.0 mmol/L). That band was set by consensus for people with diabetes, and the common goal is more than 70% of time inside it.

For someone without diabetes, the evidence points to a tighter usual range. One multicentre study in adults without diabetes (Shah et al. 2019) found about 96% of time between 70 and 140 mg/dL (3.9 to 7.8 mmol/L). Another large community cohort study (Spartano et al. 2024) reported about 3 hours a day above 140 mg/dL. Sensors differ, first-day readings are less reliable, and people differ. Treat these numbers as context, not a pass mark.

If your report shows less time in the tighter band, check whether the excursions line up with meals you already suspect. It is not automatically abnormal.

What is GMI and what does variability mean?

GMI is the Glucose Management Indicator. It estimates the A1C that would usually go with your average sensor glucose. The formula is: GMI = 3.31 + 0.02392 × average glucose in mg/dL (Bergenstal et al. 2018). It is most dependable with at least 14 days of sensor wear. It is not a measured A1C, and red blood cell lifespan or other conditions can push a lab A1C away from GMI.

Variability is how much your glucose swings around that average. Two people with the same mean glucose can have different AGP shapes: one flat, one spiky. Most AGP reports show the coefficient of variation, or CV. The international consensus on time in range set a CV below 36% as a target for people with diabetes. If you do not have diabetes, use it as a trend rather than a target. A wide outer band on the AGP is the visual version of high variability.

Why do I see lows at night?

Short, sharp overnight dips that recover by themselves are often compression lows. When you lie on the sensor, pressure on the tissue around it drops the reading fast and it recovers when you roll over. It is not your blood glucose doing that. The AGP light band may dip dramatically at 03:00 on some days but not others.

If the dip is narrow and recovers as soon as you move, treat it as probable sensor pressure. If you feel unwell, or you see lows you cannot explain, check with a finger-prick meter and talk to a doctor.

What to do next

The report only gets useful when you can see your own numbers. If you already wear a sensor, drop your LibreView, Dexcom Clarity, Stelo, Lingo or SiBionics export into the free report at https://healthosx.com/glucose and it will draw your AGP, time in range, GMI and biggest rises in the browser, no account. If you do not wear one, a month of HealthOS Sensor is $70, no membership, at https://healthosx.com/glucose/sensor.