What is insulin resistance?
Start with insulin. Insulin is a hormone — a hormone is just a chemical messenger that travels in your blood. When you eat, sugar (called glucose) goes into your blood. Insulin is the messenger that knocks on the door of your cells and tells them to open up and let that sugar in, where it is used for energy.
Insulin resistance is when your cells stop answering the knock as well as they should. The door is sticky. So your body does the obvious thing: it sends more messengers. The pancreas, the organ that makes insulin, pumps out extra to force the doors open and keep your blood sugar normal.
Here is the catch. For a long time this can work. Your blood sugar can look completely fine because all that extra insulin is quietly doing the heavy lifting. The resistance is already there, but it is hidden. Over time, if the pancreas can no longer keep up, blood sugar starts to drift upward — and that is the path toward prediabetes and type 2 diabetes. Catching the pattern early is the whole point of testing.
Which blood markers show it?
There is no single "insulin resistance test." Instead, a clinician orders a small group of blood markers and reads them as a set. Each one tells a slightly different part of the story.
The usual core is: fasting glucose (your blood sugar after not eating), HbA1c (your average blood sugar over the past few months), and fasting insulin (how much insulin your body is making at rest). From the glucose and insulin numbers, a clinician can also work out a number called HOMA-IR, which we will explain below. Many panels add two everyday cholesterol numbers — triglycerides and HDL — because the ratio between them is a useful side clue.
Almost all of these are drawn "fasting," meaning after about 8 to 12 hours with no food and only water. That is because eating temporarily spikes both sugar and insulin, which would muddy the baseline reading. One important note before we go further: the exact "normal" numbers below are reference ranges, and reference ranges differ from one laboratory to another depending on the machine and method they use. The figures here are common reference points, not hard universal lines. Your own lab report will print its own ranges, and a clinician interprets your result against those.
| Marker | Typical normal | Suggests insulin resistance |
|---|---|---|
| Fasting glucose | <100 mg/dL | 100–125 (prediabetes); ≥126 (diabetes) |
| HbA1c | <5.7% | 5.7–6.4% (prediabetes); ≥6.5% (diabetes) |
| Fasting insulin | No standardized cutoff | Use your lab's own range |
| HOMA-IR | ≈1 | ≈2.0–3.5+ (varies by sex/age) |
| Triglyceride/HDL ratio | Below cutoff | ≥≈2.5 (women) / 2.8 (men) |
| TyG index | Below cutoff | ≥≈4.65 |
What do fasting glucose and HbA1c mean?
Fasting glucose is the simplest one. It is your blood sugar level after not eating, captured at a single moment. Think of it as a snapshot.
The American Diabetes Association, a leading clinical group, sets widely used reference points for it. A fasting glucose below 100 milligrams per deciliter (mg/dL) is considered normal. A reading of 100 to 125 mg/dL falls in the prediabetes range. A reading of 126 mg/dL or higher, confirmed on more than one occasion, meets the line for diabetes.
HbA1c — say it "H-B-A-one-C," and it is also written A1C — is the longer view. Sugar in your blood naturally sticks to a protein inside your red blood cells, and those cells live for a few months. So the amount of sugar stuck to them tells you the average blood sugar over roughly the past two to three months. If fasting glucose is a snapshot, HbA1c is more like a time-lapse.
The same group sets these reference points for HbA1c: below 5.7 percent is normal, 5.7 to 6.4 percent is the prediabetes range, and 6.5 percent or higher meets the line for diabetes. Reading the two together is powerful. A one-off high fasting glucose with a normal HbA1c might just be a stressful morning; a high fasting glucose with a high HbA1c suggests a sustained pattern worth acting on.
What is fasting insulin and HOMA-IR?
This is the marker that catches insulin resistance early, and it is the one a basic checkup often skips. Fasting glucose and HbA1c both measure sugar. Fasting insulin measures the messenger itself — how much insulin your body is making just to keep that sugar normal.
Remember the hidden phase from earlier. In early insulin resistance, the pancreas works overtime, so your sugar numbers can still look perfect while your insulin number is quietly running high. Measuring insulin directly is how you can spot that the body is straining before the sugar ever budges. There is an honest limitation here, though: the lab tests used to measure insulin are not standardized across the industry, so a "normal" fasting insulin range genuinely varies from one lab to the next more than most markers do. Treat any single insulin cut-off you read online with caution, and lean on your lab's own range and your clinician.
HOMA-IR is a way to combine the glucose and insulin readings into one tidy number. The name is a mouthful — it stands for Homeostatic Model Assessment of Insulin Resistance — but the idea is simple: it estimates how hard your body is having to work to manage its blood sugar. It is not a separate blood draw; it is calculated from the fasting glucose and fasting insulin you already have. In US units the math is: fasting insulin multiplied by fasting glucose, then divided by 405. A perfectly normal, easy-running system sits near a value of 1.
What counts as "high" is genuinely fuzzy, so be wary of confident-sounding thresholds. One large study of Spanish adults found the dividing line landed somewhere between about 2 and 3.5 depending on how it was defined, and that it shifted with sex and age. That is exactly why HOMA-IR is a screening clue, not a verdict — a number that tells a clinician where to look, not a diagnosis on its own.
What about the triglyceride/HDL ratio?
There is one more clue that often comes free, because it uses two numbers already on a standard cholesterol panel. Triglycerides are a type of fat in your blood. HDL is the so-called "good" cholesterol. The triglyceride/HDL ratio is simply one divided by the other.
Why does a fat ratio say anything about insulin? Because insulin resistance tends to push triglycerides up and HDL down at the same time, so a high ratio can be an indirect fingerprint of it. A 2024 systematic review pooling 32 studies and nearly 50,000 people put the average dividing line at roughly 2.5 for women and 2.8 for men — close to the commonly cited 2.5-to-3.0 range. But, importantly, those lines are not one-size-fits-all. The same review is clear that the ratio works better in some groups than others; it is notably less reliable in people of African ancestry, where lower cut-offs (around 2.0, or even lower in some groups) may fit better. It is a helpful supporting clue, not a stand-alone test.
What is the triglyceride-glucose (TyG) index?
There is one more screening number worth knowing about, because it has a real advantage: it needs no insulin test at all. It is called the TyG index, which simply stands for the triglyceride-glucose index. Like the triglyceride/HDL ratio, it is built from cheap, everyday numbers — in this case your fasting triglycerides and your fasting glucose — so almost any standard blood panel already contains the raw ingredients.
The math is a little technical (it multiplies fasting triglycerides by fasting glucose and then takes a logarithm to keep the number manageable), but the idea behind it is simple. When the body is insulin resistant, both blood sugar and blood fats tend to run a touch high, so a number that combines the two can act as a stand-in for how hard the system is working. The TyG index was proposed for exactly this reason: the direct insulin test is expensive and, in many places, not available, so researchers looked for a way to flag insulin resistance using tests that every lab can run.
How well does it work? In the original study of about 748 apparently healthy adults, the researchers compared the TyG index against an insulin-based measure and found that a cut-off around a value of 4.65 caught most people with insulin resistance — a sensitivity of about 84 percent — but was less good at ruling it out, with a specificity closer to 45 percent. In plain words: a high TyG index is a reasonable flag to look closer, but a "normal" one does not firmly clear you, and the exact threshold shifts between studies and populations.
So the TyG index sits in the same bucket as the triglyceride/HDL ratio: a convenient, no-extra-cost screening clue, useful precisely because it skips the unstandardized insulin test, but never a diagnosis on its own. It points a clinician toward a closer look; it does not replace the fuller picture.
How is this read in context?
Here is the part that matters most, so read it twice: not one of these numbers means much on its own. A clinician reads them as a pattern, alongside things a lab value cannot see — your weight trend, blood pressure, family history, medicines, even how you slept and what you ate the day before the draw.
It also helps to see how the markers line up over the natural course of things. Early on, fasting glucose and HbA1c can stay normal while fasting insulin (and a HOMA-IR built from it) runs high — the hidden, compensated phase. If the strain continues and the pancreas can no longer keep pace, fasting glucose and HbA1c begin to drift up into the prediabetes range and beyond. Surrogate clues like the triglyceride/HDL ratio or the TyG index may flag the pattern somewhere along the way. No single one of these is the whole story; their value is in how they move together.
A normal fasting glucose with a high fasting insulin tells a very different story than a high glucose with a low insulin. A borderline HOMA-IR in a healthy, active person may mean nothing; the same number in someone with rising blood pressure and a climbing waistline may mean a lot. That judgment is exactly what a licensed clinician is trained for.
So please treat everything here as education, not medical advice. Do not diagnose yourself from a single printout, and do not change anything you are doing based on one number. Reference ranges vary by lab, the insulin test in particular is not standardized, and the meaning lives in the full picture. Bring your results to a clinician and let them connect the dots.
Keeping track of these markers with PeptidePanel
If you and your clinician are watching these markers over time, the hard part is rarely the single test — it is keeping the history straight. One result is a snapshot. The real signal is the trend across three, six, and twelve months, and that is easy to lose in a folder of PDFs.
PeptidePanel is a simple tracking tool for exactly that. You enter your lab values — fasting glucose, fasting insulin, HbA1c, and the rest — and it charts them over time so the trend is visible at a glance. It does not diagnose, prescribe, or sell any medicine or supplement, and it is not a substitute for your clinician. It is just the organized notebook that makes your next appointment more useful.