30 CGM and diabetes terms, each explained in plain English in a few sentences. Everything here is educational: definitions, not medical advice, and never dosing guidance.
A1C (HbA1c)
A blood test that reflects your average glucose over roughly the past three months, reported as a percentage (or in mmol/mol in many countries). It is the long-standing clinical reference for glucose management, and modern guidelines read it together with time in range. Convert it to everyday glucose numbers with our A1C calculator.
Ambulatory Glucose Profile (AGP)
A standardised one-page report that overlays about two weeks of CGM data onto a single 24-hour picture, showing your median glucose and the spread around it hour by hour. Clinics use it to spot patterns such as overnight drift or post-meal spikes at a glance.
Automated insulin delivery (AID)
Systems, sometimes called closed loop or hybrid closed loop, that connect a CGM to an insulin pump so the pump can adjust delivery automatically based on sensor readings. They are regulated medical devices configured with your care team. Sugar Sense is a monitoring companion and is not part of any AID loop.
Calibration
Entering a fingerstick meter value so a sensor can align its readings with blood glucose. Most current sensors are factory calibrated and need no routine fingersticks, though some still accept an optional calibration when readings look off.
CGM (continuous glucose monitor)
A small wearable sensor that measures glucose around the clock, typically every one to five minutes, and streams the readings to a phone or reader. It replaces most routine fingersticks and adds trend information a single meter reading cannot give. New to sensors? Start with our plain-English CGM guide.
Coefficient of variation (CV)
A percentage that describes how much your glucose swings relative to its average. The international consensus considers a CV of 36% or less "stable"; above that, lows become more likely. Two people can share the same average glucose with very different CVs, which is why variability metrics matter.
Compression low
A false low reading caused by pressing on the sensor, most often by sleeping on the arm that wears it. The pressure temporarily squeezes fluid away from the sensor filament, so the value dives and then recovers once the pressure is released. A surprise overnight low that snaps back within half an hour is often a compression low, but treat any low as real if you feel symptoms.
Dawn phenomenon
An early-morning glucose rise, typically between about 4 and 8 a.m., driven by the hormones that prepare the body to wake up. It is common in both type 1 and type 2 diabetes. CGM graphs make it easy to see whether your mornings follow this pattern.
Dexcom Share
Dexcom's built-in sharing service: the sensor wearer's phone uploads readings to Dexcom's servers so apps and followers can receive them remotely. Sugar Sense connects to a Dexcom account through Share; our Dexcom setup and troubleshooting guide walks through it step by step.
Estimated average glucose (eAG)
An A1C percentage translated into the same units your meter or CGM uses (mg/dL or mmol/L), via a formula from the ADAG study. An A1C of 7% corresponds to an eAG of about 154 mg/dL (8.6 mmol/L). Our A1C calculator converts in both directions.
Glucose management indicator (GMI)
An A1C-style percentage estimated purely from your CGM average glucose, useful between lab tests. It often differs from lab A1C by a few tenths of a percent because red blood cell lifespan varies between people. Estimate yours from a CGM average with our A1C and GMI calculator.
Glucose variability
How much your glucose moves around its average, captured by metrics such as standard deviation and the coefficient of variation. Lower variability generally means fewer lows and steadier days, which is why it is worth watching alongside averages and time in range.
Hyperglycemia (high glucose)
Glucose above the target range, commonly defined for CGM statistics as above 180 mg/dL (10.0 mmol/L), with above 250 mg/dL (13.9 mmol/L) counted as very high. Persistent highs deserve a conversation with your care team.
Hypoglycemia (low glucose)
Glucose below the target range, commonly defined as below 70 mg/dL (3.9 mmol/L), with below 54 mg/dL (3.0 mmol/L) treated as urgent. Lows can develop quickly, which is why real-time and predictive alerts matter; see why real-time glucose alerts matter.
Interstitial fluid
The thin layer of fluid between cells just under the skin, which is what CGM sensors actually measure. Glucose reaches it a few minutes after blood, which is the root of sensor lag and of small differences between sensor and fingerstick values.
LibreLinkUp
Abbott's follower service for FreeStyle Libre sensors: the wearer's Libre app uploads readings, and LibreLinkUp accounts can receive them remotely. Sugar Sense connects to Libre sensors through a LibreLinkUp invitation; our FreeStyle Libre guide covers the setup end to end.
MARD
Mean absolute relative difference, the headline accuracy statistic for CGM sensors: the average percentage gap between sensor readings and laboratory reference values. Lower is better; current sensors typically publish MARD values around 8 to 10%.
mg/dL
Milligrams per decilitre, the glucose unit used in the United States and a number of other countries. It measures the weight of glucose in a volume of blood. One mmol/L equals about 18 mg/dL; switch between the two with our blood sugar unit converter.
mmol/L
Millimoles per litre, the glucose unit used in the UK, Canada, Australia and most of Europe. It counts glucose molecules rather than weighing them. Divide mg/dL by 18 to get mmol/L, or use our converter with a printable chart.
Nightscout
An open-source, self-hosted platform ("We Are Not Waiting") that stores your CGM data on your own site and makes it available to apps and browsers anywhere. Sugar Sense connects to a Nightscout site with its URL and a read-only token; see our Nightscout setup guide.
Predictive low alert
An alert that fires before a low happens, by projecting the current trend a short way into the future, in contrast to a reactive alert that fires only once glucose has already crossed the line. Sugar Sense's heading-low alert is this kind of forecast, giving you time to act early.
Remote monitoring (following)
Letting chosen family members or caregivers see your glucose and receive your alerts on their own phones in real time. It is how parents watch children overnight and how partners share the load; our caregiver's guide explains how to set it up well.
Sensor lag
The few minutes by which sensor readings trail blood glucose, because sensors measure interstitial fluid. Lag is most noticeable when glucose changes fast, which is why a fingerstick and a sensor can disagree during a rapid rise or fall while agreeing at steady state.
Sensor warm-up
The waiting period after inserting a new sensor, typically 30 minutes to 2 hours depending on the model, during which the sensor settles into the tissue and gives no readings. Readings in the first day can also run slightly noisier than the rest of the wear.
Target range
The glucose band you aim to stay inside. CGM statistics use 70 to 180 mg/dL (3.9 to 10.0 mmol/L) as the standard range, with a tighter 63 to 140 mg/dL band during pregnancy. Personal targets are set with your care team and can differ from the statistical range.
Time Above Range (TAR)
The share of the day spent above 180 mg/dL (10.0 mmol/L). The consensus goal for most adults is under 25%, with under 5% above 250 mg/dL. It pairs with time in range to show where the out-of-range time actually goes.
Time Below Range (TBR)
The share of the day spent below 70 mg/dL (3.9 mmol/L). The consensus goal for most adults is under 4%, and under 1% below 54 mg/dL. Because lows are the more dangerous side, TBR is the number many clinicians look at first.
Time in Range (TIR)
The share of the day spent inside the target range, the headline CGM metric. The consensus goal for most adults is more than 70%, which is about 16 hours 48 minutes a day. Turn your percentage into hours and an approximate A1C with our Time in Range calculator, or read the full story in Time in Range explained.
Trend arrows
The arrows next to a CGM reading that show where glucose is heading and how fast: steady, rising or falling, gently or rapidly. They turn a single number into a direction, which changes how you respond to it. Our guide to reading glucose trend arrows covers each one.
Urgent low (very low)
Glucose below 54 mg/dL (3.0 mmol/L), the level consensus guidelines flag as clinically significant hypoglycemia that needs immediate attention. Alerts for this band are the ones worth keeping loud; Sugar Sense treats urgent-low alerts as its highest priority notifications.
Put the numbers to work
Three free tools pair with this glossary: the blood sugar unit converter, the A1C calculator and the Time in Range calculator.
This tool is for education only. It is not medical advice, it does not replace laboratory testing, and it must never be used for insulin dosing or other treatment decisions. Always work with your healthcare team. See our full medical disclaimer.
