What is it about?
Continuous glucose monitors (CGMs) provide scores like 'Time in Range' (TIR) to measure diabetes control. We argue that chasing a perfect score can be dangerous, an example of Goodhart's Law: when a measure becomes a target, it's no longer a good measure. This focus can lead to harmful behaviors that improve metrics but hide dangers like excessive insulin dosing resulting in frequent, sharp drops in blood sugar. We show a real-world case where a "perfect" 100% TIR report concealed 21 hypoglycemic events, as they were too brief for standard metrics to properly flag them.
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Why is it important?
As CGM use becomes standard, understanding its limitations is vital for safety. This article warns that focusing only on metrics can be misleading and can encourage a shift in practice. We urge clinicians and patients to look beyond summary statistics and review the full glucose patterns behind the numbers. This holistic view can uncover hidden risks, leading to safer and more sustainable diabetes management by helping to prevent dangerous hypoglycemic events and long-term complications.
Perspectives
As a person living with type 1 diabetes, this work is intensely personal. The clinical case presented in the article, which shows "perfect" metrics alongside significant glycemic instability, is from on my own CGM report. I realised that in my pursuit of flawless metrics, I had adopted a pathological management style, characterized by excessive insulin boluses resulting in frequent, sharp drops in glucose. The perfect summary statistics gave me and my healthcare providers a false sense of security. It was only when I began to develop premature complications that I realised my glucose management could paradoxically be the root of the problem. My hope is that this work encourages others to look beyond the summary numbers and have critical conversations about what the data truly represents, prioritizing long-term health over numerical perfection.
Dr Robert Richardson
Read the Original
This page is a summary of: Goodhart’s Law in Diabetes Care: The Hidden Drawbacks of Overoptimizing CGM Metrics, Diabetes Care, September 2025, American Diabetes Association,
DOI: 10.2337/dc25-1985.
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