“The Number Said I Was Fine”: When a Dexcom CGM Gives a Wrong Reading

Medical device guides · 13 min read · Published 10 November 2026 · Reviewed 10 November 2026 · Next review May 2027

By Dr Rosemary Listing, PhD (Law) · Medical negligence lawyer since 2014 · Of Counsel, Peter Evans & Associates

If a CGM reading let you or your child down, I want you to know that trusting it was reasonable. These devices are prescribed so that people can rely on them. Your questions about what went wrong are entirely fair.

This guide covers how CGMs work, when to double-check, recalls, what to keep as evidence, who may be responsible, and how the law looks at it.

Start with your question

• How does a Dexcom CGM work?
• What if my Dexcom reading doesn’t match my symptoms?
• Have Dexcom sensors been recalled in Australia?
• What should I keep if my CGM was wrong?
• Who is responsible if a CGM gives a wrong reading?
• How do I report a faulty CGM?
• Could this be negligence or a product claim?

How a CGM works

A continuous glucose monitor uses a small sensor placed just under the skin, usually on the tummy or the back of the arm, that measures glucose around the clock and sends readings to a reader or phone. Sensors are replaced every 7 to 14 days depending on the device.¹ Even with a CGM, you will still sometimes need a finger-prick test.¹

Approved places to wear a sensor differ between models and ages. Follow the instructions for your device, and ask your diabetes educator if you are unsure.

Training and advice

When a CGM is started, you should be shown how to insert it, read it, set alarms and respond to them, and when to check with a finger prick instead. healthdirect suggests asking your diabetes educator when you should finger-prick.¹

Questions to ask your diabetes team

• When should I check with a finger prick instead of trusting the CGM?
• What alarm settings are right for me or my child?
• Where can I wear the sensor?
• What should I do if the sensor fails or the readings seem wrong?

When the number doesn’t match how you feel

Diabetes WA advises that if readings are missing or don’t match the signs and symptoms you are experiencing, you should always check with a finger prick before making insulin or food decisions.² healthdirect also recommends checking readings when glucose is low or very high.¹

Low glucose: worth checking, or emergency

Recalls and alerts

In May 2026, the National Diabetes Services Scheme reported a TGA market alert about two Dexcom G7 sensor batches supplied through unofficial channels. They had been set aside for disposal in the United States after testing found possible incomplete sterilisation and a risk of failure, and were reportedly stolen and resold. NDSS-supplied sensors were not affected.³ Recalls are listed by the Therapeutic Goods Administration.

What to keep

• The sensor itself, its applicator and packaging, with the lot number
• Screenshots or an export of the app data around the event
• Finger-prick readings and meter memory
• Ambulance and hospital records
• Where you bought the sensor

Reporting a problem

Tell the manufacturer, your diabetes team and the TGA. Reports help identify faulty batches. Diabetes WA notes manufacturers will often replace a sensor that fails early,² but if harm occurred, ask that the sensor be kept or returned for testing rather than simply replaced.

Who may be responsible

A wrong reading can raise two different questions. One is about the device: was the sensor defective? That is a question about the manufacturer or supplier. The other is about care: were you properly trained, was your hypo plan clear, and did doctors or nurses rely on a CGM reading when your symptoms said otherwise? In hospital, for example, a reading that doesn’t match a patient’s condition should prompt a blood test. Our medication, drug and device harm page explains how product and care claims differ.

What to look for in the records

Your records are often where the story becomes clear. You have a right to access your own health information. In NSW the Health Records and Information Privacy Act 2002 covers both public and private providers, and the Information and Privacy Commission explains how to ask.⁴ Our step-by-step guide to getting your medical records in Australia walks you through it.

How the law looks at it

A wrong CGM reading is not automatically anyone’s fault. Sensors are not perfect, and there is a known difference between sensor and blood readings. The legal questions depend on the cause: whether the device was defective, whether the care and training you received met the standard expected, and whether either caused harm.

A claim usually turns on three questions: whether the care fell below what peers would widely accept as competent practice (section 5O of the Civil Liability Act 2002 (NSW))⁵, whether that shortfall probably caused harm you wouldn't otherwise have had (Tabet v Gett)⁶, and, where it matters, whether you were told the material risks first (Rogers v Whitaker)⁷⁸. Our guide to how a medical negligence claim works explains each one in plain terms.

In a CGM case, the questions might be: were you trained in when to check with a finger prick? Did your hypo plan cover a mismatch between symptoms and readings? In hospital, did staff check a blood glucose when the CGM didn’t match your condition? Separately, was the sensor faulty or from a recalled batch?

In plain terms, the question is whether proper training, a blood check, or a sensor that worked as it should would probably have avoided the severe low or high.

For a CGM, the relevant information is usually about its limits and when not to rely on it alone.

Who can claim, and when

The person harmed can claim. A claim for a child is usually brought by a parent on the child’s behalf. In NSW, time usually runs from when you knew, or ought to have known, enough to claim, not from the treatment itself, and courts can sometimes extend it, so an old injury may still count. See time limits in NSW or other states, and ask early.

More: complaint or claim? · how a claim is paid for · what a claim can cover

In my practice

In device files, I often find that the device and the care are tangled together. A family assumes the sensor failed; the records show nobody explained when to double-check. Or a hospital team trusts a reading on the screen over a confused patient in front of them. Keeping the sensor and the data matters, because without them it is very hard to tell which it was.

Both things can be true

Your CGM may have made life much better, and it may still have failed on the night it mattered. Your diabetes team may have been supportive, and the training may still have missed something important.

The bigger picture

CGMs are now widely subsidised in Australia, which means more people rely on them every day. You can check a practitioner’s registration on the Ahpra public register,⁹ and complaints about care in NSW can go to the Health Care Complaints Commission.¹⁰

See also our guides to pacemaker failure and the Exactech knee recall.

Support

You don't have to work through this alone. These services can help:

• Lifeline, 24-hour crisis support: 13 11 14 (listed on healthdirect's helplines page)¹¹
• Beyond Blue, anxiety and depression support: 1300 22 4636
• Medicare Mental Health, help finding mental health support: 1800 595 212
• healthdirect, 24-hour nurse advice: 1800 022 222
• Health Care Complaints Commission (NSW): 1800 043 159

A mother on a bathroom floor, staring at a screen that said everything was fine, now knows what to keep and what to ask. You deserve those answers too.

With care,
Rosemary

Frequently asked questions