Foundations — Part 9

Measuring T1D Success

There are dozens of metrics you could track. Tracking too many, too soon, is a reliable route to confusion. This page focuses on three measures that are easy to know, easy to revisit, and together explain most of what matters day to day.

The three core measures

“What gets measured gets managed.”

In diabetes, measuring everything is a reliable way to manage nothing — except burnout.

The three measures worth focusing on are:

Time in range — percentage of time between 3.9–10.0 mmol/L (70–180 mg/dL).
HbA1c — reported as mmol/mol or %; a blunt tool, but useful when interpreted in context.
Total daily insulin dose — units per kilogram per day (U/kg); often overlooked, yet it reveals a great deal about physiology and insulin sensitivity.

Two other measures matter enormously — blood lipids (particularly ApoB, or non-HDL / LDL cholesterol as alternatives) and blood pressure. GNL is working on dedicated guides for how to think about these properly. Hard numbers without context can create more confusion than clarity in an area with a lot of noise and conflicting advice. To be notified when those guides are published, subscribe to the GNL Weekly Brief.

1. Time in range (3.9–10.0 mmol/L or 70–180 mg/dL)

Time in range is a measure you will have encountered throughout the Foundations guide. Here is the current international consensus on glucose targets.

Consensus CGM targets showing recommended percentages for time in range, time below range (level 1 and 2), and time above range (level 1 and 2).

70% time in range is a solid, realistic first milestone. With Dynamic Glucose Management, 70% is the starting point — not the ceiling.

The table below helps explore what different TIR targets might mean in terms of effort and attention. It is worth picking a target that feels genuinely achievable rather than aspirationally unrealistic.

Trade-off graphic showing that higher time in range is associated with better outcomes but also with increasing effort and attention required.

To reach a higher TIR, the high alert threshold needs to be set accordingly — and the GAME strategy for stopping highs becomes important. Improving by around 5% every few weeks tends to be more sustainable than a dramatic overnight change.

2. HbA1c (mmol/mol or %)

HbA1c measures how much glucose has become attached to red blood cells. Higher HbA1c reflects higher average glucose over roughly the last three months.

Diagram illustrating HbA1c as glucose molecules attached to red blood cells, reflecting average glucose over approximately three months.

The landmark DCCT trial showed that the risk of microvascular complications tends to rise as HbA1c increases. HbA1c is a useful predictor of long-term risk — though it is a blunt tool when used in isolation.

DCCT study figure showing that higher HbA1c associates with progressively higher risk of microvascular complications in type 1 diabetes.

A widely-used headline goal is HbA1c ≤ 48 mmol/mol (6.5%). Keeping time in range above around 80% makes this target very achievable for many people.

Important caveat: in some people — particularly those with certain haemoglobin variants or darker skin tones — HbA1c can run higher (or lower) than time in range would predict. If this applies to you, this explanation of why the relationship isn’t always straightforward is worth reading.

3. Total daily insulin dose (U/kg)

Total daily dose tells you a great deal about insulin sensitivity and underlying resistance. The adult range is broad: roughly 0.4 to 1.0 U/kg, and in some cases up to 2.0 U/kg.

Illustrative examples of typical ranges:

A 75 kg adult often uses 30–75 units/day (upper range up to ~150 units).
A 60 kg adult often uses 24–60 units/day (upper range up to ~120 units).

In adults, doses tend to distribute roughly as follows:

0.4–0.5 U/kg — insulin sensitive (~10% of people with T1D)
0.5–0.7 U/kg — some insulin resistance (~30%)
0.7–1.0 U/kg — significant insulin resistance (~50%)
More than 1.0 U/kg — high insulin resistance (~10%)

In children aged 1–12, the same broad range applies. During puberty (roughly ages 12–18), insulin needs often rise due to hormonal changes — see the relevant puberty and insulin requirements data:

0.4–0.6 U/kg — insulin sensitive (~10%)
0.6–0.8 U/kg — resistance emerging (~30%)
0.8–1.2 U/kg — significant resistance (~50%)
More than 1.2 U/kg — high resistance (~10%)

If you find your dose sits in the higher ranges, this is common — around half of people with T1D fall into the significant resistance category. The Insulin resistance in T1D guide covers practical approaches.

The smart play here is to improve from where you are now, rather than comparing yourself to the most insulin-sensitive end of the range:

If currently above 1.0 U/kg, moving below 1.0 U/kg (while maintaining glucose control) is a meaningful improvement.
If around 0.7 U/kg, getting to 0.6 U/kg while holding glucose steady is serious progress.

Important: do not sacrifice glucose control just to reduce insulin dose. Lower insulin with higher glucose is not a good trade. Improving insulin sensitivity only matters if you maintain or improve control at the same time.

If insulin resistance is your main barrier, this guide covers how to work on it systematically: Overcoming insulin resistance in T1D.

What this means in practice

Focus on time in range, HbA1c, and total daily insulin dose first — these three measures are easy to know, easy to revisit, and explain most of what matters day to day.
70% TIR is a good starting milestone. With Dynamic Glucose Management, it is achievable for most people — and improvable from there.
HbA1c is a useful long-term signal but has limitations, especially in people with certain haemoglobin variants.
Total daily insulin dose per kilogram reveals where you sit on the insulin sensitivity spectrum — and gives a target for incremental improvement.
Improve gradually rather than making dramatic changes. Sustainable progress compounds over time.

This content is for educational exploration only. It describes average responses and general principles. It is not medical advice and cannot replace individual clinical guidance from your diabetes care team.

Congratulations — you’ve completed the Foundations guide

You have built a strong conceptual foundation. The next step is applying it.

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