Traditional biomarkers like your blood glucose/blood sugar can help to indicate how healthy you are. But they don’t always capture the full picture of your metabolic health. That’s why most medical professionals use more advanced blood sugar-related measurements, like insulin levels and A1C, to assess health and chronic disease risk.
That said, these two measures aren’t equally useful. As research would show us, they’re not always reliable when evaluating metabolic or cardiovascular health.
Below, I’m breaking down what it means to measure your insulin vs A1C, including which one is more valuable to metabolic health.
Insulin
Insulin is a hormone that your pancreas makes to help your cells absorb blood glucose (sugar) to use as energy or store for later. If you don’t make enough (e.g. if you have type 1 diabetes), or if your cells become resistant, glucose builds up in the bloodstream. This can ultimately lead to metabolic dysfunction and chronic illnesses like type 2 diabetes.
You can learn more about insulin resistance here.
How to measure insulin
One of the most common measures of insulin is a fasting insulin test. This typically requires a blood draw or finger prick.
An elevated insulin level is an indicator of developing insulin resistance, which can be more completely assessed in a few way.
Other lab tests, like an Oral Glucose Tolerance Test (or OGTT), are better at detecting glucose dysregulation than measuring insulin resistance.
A more accurate measure is known as the Homeostasis Model Assessment of Insulin Resistance, or HOMA-IR. Not only is it one of the most validated assessments of insulin resistance, but it combines multiple measures (like your fasting plasma glucose and fasting plasma insulin levels) to calculate a score between 1 and 5. Anything less than 1 means you’re very insulin sensitive. Anything higher than a 2.8 may indicate significant insulin resistance.
But another, even more reliable test is the Lipoprotein Insulin Resistance Score (LPIR). Instead of measuring glucose or insulin directly, LPIR examines the size and concentration of cholesterol-carrying particles. These typically change when your cells become resistant to insulin, which means you may be able to detect insulin resistance somewhat earlier than traditional glucose tests. The lower the score (down to 0), the more insulin sensitive you are. The higher your score, typically a 100 max, indicates you’re insulin resistant.
You can learn more about the advanced lipid measurements your doctor doesn’t know about here.
What abnormal insulin readings tell you
High levels of insulin or signs of insulin resistance typically mean you’re suffering from hyperinsulinemia. This can eventually progress to much worse chronic diseases, including Alzheimer’s, which is widely regarded as type 3 diabetes.
Interestingly, we also have quite a bit of information showing that insulin resistance is a stronger risk factor for heart disease than your A1C. But we’ll get into this later on.
In the meantime, you’re welcome to check out this guide explaining the earliest signs of insulin resistance.
A1C
A1C, sometimes called an HbA1c, measures your average blood sugar levels over the past three months. That’s because most red blood cells live about three months, and a blood draw can help detect glucose attached to the hemoglobin in your red blood cells.
Your A1C can give you a better long-term picture of blood sugar control than your average fingerprick test or CGM number. But it doesn’t necessarily determine whether or not you’re insulin resistant, as we’ll explore below.
How to measure A1C
You can order an A1C test from your primary care provider at any time, usually without needing a 12-hour fast. You’ll give blood via a finger prick or a typical full-panel blood draw. Then, technicians will analyze the percentage of your hemoglobin that has glucose attached to it, expressed as a percentage.
A ‘normal’ A1C is typically at or below 5.6%, while prediabetes is 5.7% to 6.4%. Most medical professionals diagnose diabetes at 6.5% or higher.
What abnormal A1C readings tell you
As mentioned, a high A1C above 5.6% typically means you have diabetes or prediabetes. It also means you may be suffering from insulin resistance, although this test can’t necessarily confirm that on its own.
You should also keep in mind that CGMs can’t always accurately assess your A1C. Most are only designed to measure daily blood sugar trends, after all, and not necessarily long-term trends.
But does a high A1C mean you’re destined for heart disease? Not necessarily.
Let’s take a closer look.
A1C vs insulin test for measuring metabolic health
While traditional medical professionals may see your A1C as a gold standard of metabolic health, the truth is that it’s quite variable depending on the day.
One study found that “there are a variety of clinical scenarios that may result in falsely elevated or falsely lowered A1C values.”
This is because:
- Many lab tests allow for a ± percentage in both directions. First, you should know that A1C tests have a very wide range of accepted accuracy. Here’s how one VA.gov medical resource page describes this: “The A1C result is reported as a percentage. Like many lab tests, the A1C can vary by plus or minus 0.5%. This means you should consider an A1C result within a range. For example, an A1C of 7%, reflects a range of 6.5% to 7.5%.” Now, think about how this could affect you if you have a reading of 5.6. This means you could be within a normal range. Or you could be prediabetic.
- There is variance between labwork providers. Federal law accommodates up to 8% variation in lab readings (according to 2025 CLIA Acceptance Variance for Proficiency Testing). So even if you get a 5.8 A1C result from Quest, for example, LabCorp might send back a 5.336 A1C. Your Quest reading would indicate diabetes, but your LabCorp reading would not.
- Many different factors can raise or lower your A1C. Apart from blood sugar, your A1C may be falsely elevated if you consume alcohol or opioids, are iron-deficient, or take large amounts of vitamin C before certain tests. In contrast, you may have falsely lowered A1C readings if you’re pregnant, suffer from hemolytic anemia, or take large amounts of vitamin E.
- There may be racial and ethnic differences in the average glucose value. For example, Caucasians may have lower absolute A1C readings than other ethnicities. Scientists aren’t completely sure why these differences exist.
To be fair, we also know that insulin tests can be widely variable depending on the type you order. A fasting insulin test can range widely, for example. Stress, sleep, and even what you ate the night before can have a significant impact on your readings.
You should also know that insulin is secreted in pulses and has a very short half-life (roughly five minutes or less). This means some insulin measurements can be prone to error. It also suggests that a single day of results is not enough to make accurate judgments about your health.
At the end of the day, both insulin and A1C can indicate changes to your metabolic health. But if you had to choose one measure, I’d say start with your insulin measurements first.
For the best possible measurements, I would recommend a three-point measure:
- Fasting insulin (under eight for best results)
- HOMA-IR and/or LPIR to check for insulin resistance
- CRP and myeloperoxidase to check for inflammation
These make for an excellent baseline when used together. But they can be stronger still when combined with other data points in an advanced lab panel.
I provide several recommendations for blood tests to try, along with other resources, on my website. I also have resources explaining how to interpret your lab results. Or, if you don’t want to interpret them yourself, explore how I can help at ifixhearts.com/talk.
