Insulin Resistance: What It Is and How Doctors Measure It

Maybe you read online that insulin resistance is behind weight gain, tiredness, or cravings. Maybe your clinician said your labs "suggest insulin resistance". You may wonder why no one has ordered a test called "insulin resistance". This guide explains what it is, why it is hard to measure, and what clinicians use instead.

What insulin does

Insulin is a hormone made by the pancreas. After you eat, glucose (sugar) enters your blood. Insulin helps move that glucose into your muscles, fat, and liver, where it is used or stored [1].

What insulin resistance means

In insulin resistance, your muscles, fat, and liver do not respond well to insulin [1]. Glucose has a harder time getting into cells. The pancreas makes more insulin to keep up.

For a long time, this extra insulin keeps blood sugar normal. Over time, the pancreas may not keep up. Blood sugar rises, first into the prediabetes range and later into type 2 diabetes [1].

What raises the risk

Insulin resistance is linked to [1]:

• Extra body fat, especially around the belly and in the liver
• Low physical activity
• Family history and genetics
• Older age
• Some medicines, such as steroids and some antipsychotics
• Poor sleep and sleep apnea
• Conditions such as polycystic ovary syndrome (PCOS)

Signs you might notice

Insulin resistance usually has no symptoms. Some people have:

• Dark, velvety patches of skin on the neck, armpits, or groin (acanthosis nigricans) [1]
• Skin tags
• A large waist size

What your doctor looks at

Why there is no routine test

The most accurate measure is the clamp test, which infuses insulin and glucose for hours in a research lab. It is not used in normal care.

HOMA-IR is a formula that estimates insulin resistance from fasting glucose and fasting insulin [2]. It was developed for research, and it works best for comparing groups of people [2]. Insulin tests are not standardized well between labs, so the same blood can give different numbers. For these reasons, HOMA-IR and fasting insulin are not part of routine care in most guidelines.

What clinicians use instead

Clinicians look for a pattern of results that often comes with insulin resistance. This pattern is called metabolic syndrome. A joint statement from several international groups, including the American Heart Association and the National Heart, Lung, and Blood Institute, defines metabolic syndrome as having 3 or more of these 5 findings [3]:

• Large waist size, using cutoffs that differ by population and country. In Canada and the US, common cutoffs are 102 cm (40 inches) or more for men and 88 cm (35 inches) or more for women.
• Triglycerides of 1.7 mmol/L (150 mg/dL) or higher, or treatment for high triglycerides
• HDL cholesterol below 1.0 mmol/L (40 mg/dL) in men or below 1.3 mmol/L (50 mg/dL) in women, or treatment for low HDL
• Blood pressure of 130/85 or higher, or treatment for high blood pressure
• Fasting glucose of 5.6 mmol/L (100 mg/dL) or higher, or treatment for high glucose

Diabetes Canada also describes metabolic syndrome and uses similar criteria [4]. Lower waist cutoffs are used for some groups, such as people of South Asian, Chinese, or Japanese background [3].

Other clues

• A1C or fasting glucose in the prediabetes range
• Fatty liver on ultrasound or raised liver tests
• A high ratio of triglycerides to HDL cholesterol
• A history of gestational diabetes or PCOS

What helps

Insulin resistance responds well to lifestyle changes.

• Physical activity. Muscles take up glucose during and after exercise, even with less insulin. Both aerobic exercise and strength training help.
• Weight loss if you have extra weight. In the Diabetes Prevention Program, about 7% weight loss plus 150 minutes of activity a week cut the chance of type 2 diabetes by 58% [5].
• Eating patterns that you can keep up, with fewer sugary drinks and highly processed foods.
• Better sleep and treatment of sleep apnea.
• Not smoking.

Medicines such as metformin can improve insulin sensitivity. They are used for diabetes and sometimes for prediabetes or PCOS. Talk to your clinician or pharmacist before you start any medicine.

Linked conditions

Insulin resistance often appears together with other conditions. If you have one, your clinician may check for the others:

• Prediabetes and type 2 diabetes
• High blood pressure
• High triglycerides and low HDL cholesterol
• Fatty liver disease (MASLD)
• Polycystic ovary syndrome (PCOS)
• A history of gestational diabetes
• Sleep apnea

These conditions share many of the same root causes. The same lifestyle changes help all of them.

Questions to ask your clinician

• Do my test results suggest insulin resistance or metabolic syndrome?
• What are my A1C, fasting glucose, triglycerides, and HDL?
• What is my waist size, and what cutoff applies to me?
• Would a fasting insulin test change my care?
• Should I be checked for fatty liver or sleep apnea?
• What type and amount of activity would help me most?
• How often should my blood sugar be checked?

When to get care quickly

Insulin resistance is not an emergency. Get medical care soon if you have strong thirst, frequent urination, blurred vision, or weight loss without trying. These can be signs of diabetes.

Bottom line

Insulin resistance means your body needs extra insulin to keep blood sugar normal. There is no standard routine test, so clinicians look at waist size, blood pressure, triglycerides, HDL, and glucose. Activity and weight loss are the most effective ways to improve it.

Primary AI can show you the guideline and study sources behind this topic in plain language, so you can bring better questions to your appointment.