Three delays, not one
When people talk about “CGM delay” they often mean different things. Between the glucose in your blood and the number on a follower’s screen or your watch, there are three separate steps, and each one adds time:
| Step | What happens | Typical effect |
|---|---|---|
| 1. Your body | Glucose moves from blood into the fluid under your skin | Several minutes, more when glucose moves fast |
| 2. Sensor and phone | The sensor reads at intervals and sends to your phone app | Up to one interval: 1 to 5 minutes depending on the sensor |
| 3. Sharing service | Your phone app uploads to the maker’s cloud, others read it there | Usually short, sometimes several minutes |
1. Your body: from blood to fluid
A CGM doesn’t sit in a blood vessel. Its filament sits in the fluid between your cells, just under the skin, and measures the glucose there. Glucose has to travel from your blood into that fluid, so the fluid follows blood glucose with a lag usually described as somewhere between 5 and 15 minutes.
When glucose is steady you hardly notice. When it moves fast, after a meal or during a hard workout, the lag shows: the sensor may still be reporting where you were a few minutes ago. That’s also why a CGM and a fingerstick can disagree at those moments.
2. Your sensor and your phone
Sensors don’t send a continuous stream. They send a reading at regular intervals to the sensor maker’s app on your phone. Dexcom G6 and G7 send one every five minutes. FreeStyle Libre 3 updates your phone every minute. Other sensors have their own rhythm, and a Nightscout site shows whatever its uploader sends.
So on top of the body’s lag, the latest reading can be up to one interval old before your phone even has it.
3. The sharing service
To reach anyone or anything beyond your phone (a follower, a watch app, Ando) each reading goes through the sensor maker’s cloud: Dexcom Share, LibreLinkUp, CareLink or Medtrum EasyFollow. Your phone app uploads it, the service publishes it, and followers read it from there.
Most of the time this takes a few seconds to a couple of minutes. It takes longer when your phone is offline or in low-power mode, when the sensor app has been closed in the background, or when the service itself is busy. Those are the moments followers notice a delay.
Keep your sensor app installed and signed in, allow it to run in the background, and keep your phone online. The setup guides for Dexcom Share and LibreLinkUp list the usual culprits.
How fresh the glucose in Ando is
Ando reads your glucose from the sharing service, so it inherits the three delays above. On top of them:
- With Live on, Ando checks for a new reading about every five minutes and sends it to your lock screen, Dynamic Island, watch or Android notification as soon as it arrives. If the reading isn’t published yet, it checks again within seconds.
- When you open the app, Ando fetches your latest readings straight away.
- In the background, Ando keeps your history up to date about every hour, so your workouts, nights and weekly wrap fill in even when you don’t open it.
Live always shows when the reading was taken, so you never mistake an old number for a new one.
When readings stop
If no new readings arrive for a while, the cause is almost always upstream: the phone is off or offline, the sensor is warming up or has ended, the sensor app was signed out, or the sharing service is having a moment. Ando shows a notice in the app if your glucose stops arriving, with the usual fixes for your sensor.
Once the connection is back, readings that reached the cloud in the meantime fill in on your timeline. Read more in glucose at night about gaps on the overnight line.
Questions people ask
How long is the Dexcom Share delay?
There are two parts. The sensor itself reads glucose in the fluid under your skin, which trails blood glucose by several minutes, and it sends a reading every five minutes. Then the Dexcom app uploads each reading to Dexcom Share, which adds its own delay, usually short but sometimes several minutes when the service is busy or your phone is offline.
Why is LibreLinkUp behind my Libre app?
LibreLinkUp only sees a reading after your Libre app has uploaded it to Abbott’s cloud. If your phone is offline, the Libre app is closed in the background or the cloud is slow to publish, the follower view falls behind the sensor app.
Is Ando real time?
Close to it. When Live is on, Ando checks your sensor’s cloud for a new reading about every five minutes and sends it to your lock screen and watch as soon as it arrives. Each update shows when the reading was taken.
Does Ando work if my phone is off?
Your sensor’s own app sends readings to the cloud from your phone. If the phone is off or offline, no new readings reach the cloud, so Ando cannot see them either until the connection is back.
Why does my CGM differ from a finger prick?
A fingerstick measures glucose in your blood right now; a CGM measures it in the fluid under your skin, a few minutes behind. When glucose is moving quickly, after a meal or during exercise, the two drift apart. Sensor makers advise a fingerstick check when a reading does not match how you feel.