When patients think about diabetes or metabolic health, they usually think of blood sugar. That is understandable: glucose is one of the measurements we commonly use to assess how the body manages sugar.
But glucose doesn’t tell the whole story.
Your body may sometimes be working considerably harder to keep your blood glucose within its expected range. One hormone involved is insulin. This means looking at glucose alone may not always show the full metabolic picture.
What happens after you eat?
When we eat carbohydrates, the body breaks them down into glucose, which enters the bloodstream. In response, the pancreas releases insulin. Insulin helps glucose move from the bloodstream into cells, where cells can use it for energy.
In a healthy system, this process works very efficiently. But when cells become less responsive to insulin, the body may compensate by producing more. This is where insulin resistance becomes important.
Can glucose still be normal?
Yes. In the early stages of insulin resistance, the pancreas may compensate by producing more insulin. As a result, someone’s glucose may remain within the expected range while their body relies on higher insulin levels to achieve it.
I often describe this to patients as looking not only at the outcome, but at how hard the body has to work to achieve it. Eventually, if the pancreas can no longer compensate sufficiently, glucose levels may begin to rise. This is one pathway through which prediabetes and type 2 diabetes can develop.
You can’t diagnose insulin resistance from one number alone. However, it can be an important part of the bigger picture of someone’s metabolic health.
It is associated with conditions and risk factors including type 2 diabetes, metabolic syndrome, obesity and polycystic ovary syndrome (PCOS). Importantly, insulin resistance may not cause obvious symptoms.
Some patients investigate their metabolic health because of symptoms such as persistent fatigue, weight changes, increased hunger, or other concerns. Others have no symptoms but may have risk factors such as a family history of type 2 diabetes.
None of these symptoms automatically mean someone has insulin resistance, which is why appropriate assessment matters.
Fasting glucose & fasting insulin are not the same thing
This is one area patients can understandably find confusing. A fasting glucose measurement tells us how much glucose is present in the blood after fasting. A fasting insulin measurement tells us how much insulin is circulating while you are fasting. Together, these measurements can provide information that one measurement alone cannot.
Another calculation you may encounter is HOMA-IR, which uses fasting insulin and fasting glucose measurements to estimate insulin resistance.
Should everyone have their insulin tested?
Not necessarily. More testing is not automatically better medicine. Whether a fasting insulin measurement is useful depends on the individual, their medical history, symptoms, risk factors and what question we are trying to answer.
Blood tests are most useful when you have a reason to do them and when you interpret the results in context.
If you are specifically concerned about diabetes, established tests can investigate and diagnose it, and your clinician can advise which investigations are appropriate.
What if my fasting insulin is high?
A higher fasting insulin result may indicate insulin resistance, but it shouldn’t be interpreted on its own.
We may need to consider your glucose result and other markers alongside factors such as your medical history, medications, family history, weight, blood pressure and cholesterol. Most importantly, a high fasting insulin result does not automatically mean you have diabetes. It needs to be put into context.
Looking beyond a single number
One difficulty with health testing is that it’s easy to focus on whether an individual result is simply labelled “normal” or “abnormal”. As a doctor, I am usually more interested in the wider picture.
What was the reason for testing? What are the other results showing? Are there relevant symptoms or risk factors? Has something changed over time?
When we approach metabolic health this way, blood tests become much more useful than isolated numbers on a laboratory report.
If you would like to investigate your insulin and glucose levels, City Walk-In Clinic offers a dedicated fasting insulin blood test, which includes fasting glucose and HOMA-IR.
Medically reviewed by Dr Kate Soffer, General Practitioner
