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Module 2 of 3 · Insulin Resistance & Prediabetes 101

What Your Labs Are Telling You

LaVera J. Forbes, PhD, MS, CHN

About 25 minutesUses the Lab Markers Calculator and Worksheet

Please note: This course is educational. It does not diagnose or treat any condition, and it does not replace your medical care. Use your numbers to start a conversation with your doctor, not to diagnose yourself.

Grab the lab report and waist measurement from Module 1. This is where you find out what your numbers are really saying.

The standard ranges

These are the ranges your doctor most likely uses. They come from NIDDK, part of the National Institutes of Health.

Test	Normal	Prediabetes	Diabetes
HbA1c	Below 5.7%	5.7–6.4%	6.5% or higher
Fasting glucose	Below 100 mg/dL	100–125 mg/dL	126 mg/dL or higher
2-hour glucose test*	Below 140 mg/dL	140–199 mg/dL	200 mg/dL or higher

*The 2-hour glucose test (oral glucose tolerance test) is an official diagnostic test, but it's used less often in routine checkups.

"Normal" is not the same as optimal

Standard ranges are designed to catch disease once it's there. A functional approach asks where your body is heading. Mrs. D.'s glucose and HbA1c were both normal. They just weren't telling the whole story.

Glucose shows the result. Fasting insulin shows the effort behind it. To see that effort, you need a few more numbers. Most are inexpensive and often covered by insurance, and you may already have some of them.

Marker	What it tells you	How to get it
Fasting insulin	How hard your pancreas is working to keep glucose normal. It often rises years before glucose does. (Tabák et al., 2009)	Ask for it. It's usually not on a standard panel.
HOMA-IR	An insulin resistance score from fasting glucose and fasting insulin.	Use the calculator or worksheet.
TyG index	An insulin resistance score from fasting triglycerides and glucose.	Calculate it from labs you likely already have.
Triglyceride-to-HDL ratio	A higher ratio has been linked to insulin resistance and heart disease.	Divide triglycerides by HDL from your cholesterol panel.
hs-CRP	Low-grade inflammation, which feeds insulin resistance.	Ask your doctor to add it.
Waist measurement	Fat around your organs, which drives insulin resistance more than total weight.	A tape measure at home.

Functional optimal ranges

Some standard lab ranges, like the one for fasting insulin, are based on averages from a population where metabolic problems are very common. So "normal" can still mean "on the way to trouble." Functional optimal ranges aim for what a healthy body looks like, so you can spot changes years earlier.

Marker	Standard "normal"	Functional optimal	Why it matters
HbA1c	Below 5.7%	4.6–5.2%	Research suggests heart disease risk may begin to rise even in the upper 5% range, below the diabetes range.
Fasting glucose	Below 100 mg/dL	72–86 mg/dL	Glucose that keeps running above the mid-80s can mean your pancreas is already working harder.
Fasting insulin	Many labs allow up to 20–25 µIU/mL	2–5 µIU/mL	Low insulin keeps your body flexible, able to burn stored fat instead of staying in storage mode.
HOMA-IR	No official range	Under 1.0	A score above 1.0 can be an early sign that your pancreas is working overtime, long before glucose rises.
Triglyceride-to-HDL ratio	No official range; researchers have flagged insulin resistance at about 3	Under 1.0	In research, this ratio was one of the strongest predictors of heart attack risk.

After a meal, a healthy body keeps glucose well below 140 mg/dL with a small, short rise in insulin. Both come back close to fasting levels within about two hours.

Functional optimal ranges are goals many functional medicine practitioners use. They are not official diagnostic criteria, and research is still catching up on some of them. Use them as targets to discuss with your care team, not as a diagnosis.

Your quick win: run your numbers

Calculate your markers

Example values Replace them with your own fasting results.

Fasting glucose (mg/dL) Fasting insulin (µU/mL) Fasting triglycerides (mg/dL) HDL cholesterol (mg/dL) Waist (inches) Sex

–HOMA-IR

–TyG index

–Triglyceride-to-HDL ratio

–Waist vs US cut-point

The usual US waist cut-points are 35 inches for women and 40 inches for men. Some groups, including Asian Americans, tend to develop problems at smaller waist sizes.

This calculator does not diagnose anything, and your numbers stay in your browser. Bring them to your doctor and track them over time.

Prefer paper? Download the printable Lab Markers Worksheet (PDF)

Use fasting results from the same blood test, in US units (mg/dL).

1. HOMA-IR (needs fasting insulin)
HOMA-IR = glucose × insulin ÷ 405
Example: glucose 104, insulin 12. 104 × 12 ÷ 405 = 3.08.

HOMA-IR score	What it suggests
Under 1.0	Functional optimal insulin sensitivity
1.0–1.9	Above the functional optimal range; early changes may be starting
2.0–2.9	Early insulin resistance
3.0 or higher	Significant insulin resistance

Research studies use different HOMA-IR cut-offs depending on the population, so treat these as a guide, not a diagnosis.

2. TyG index
TyG = ln(triglycerides × glucose ÷ 2)
Example: triglycerides 160, glucose 104. 160 × 104 ÷ 2 = 8,320. ln(8,320) = 9.03.
("ln" is the natural log. On most phones, turn the calculator sideways to find the ln button.)

3. Triglyceride-to-HDL ratio
TG/HDL = triglycerides ÷ HDL
Example: triglycerides 160, HDL 45. 160 ÷ 45 = 3.6. The functional optimal goal is under 1.0.

This is the easiest place to start. If you have a cholesterol panel, you can do this one today.

4. Waist
Measure at the level of your navel, standing relaxed, after you breathe out.

	Common US cut-point
Women	35 inches or more
Men	40 inches or more

Some groups, including Asian Americans, tend to develop problems at smaller waist sizes.

Where am I on the path?

Use this as a rough guide to bring to your doctor. It is not a diagnosis.

What your numbers show	What it may suggest
Glucose and HbA1c normal, but fasting insulin, HOMA-IR, TG/HDL, or waist above the optimal range	Possible insulin resistance with blood sugar still holding steady. This is the most responsive stage.
Fasting glucose 100–125 mg/dL or HbA1c 5.7–6.4%	Prediabetes by the NIDDK definition, very often with insulin resistance underneath.
Prediabetes-range glucose or HbA1c and high insulin markers	Both. Your pancreas is working hard, and blood sugar has started to rise. Still very responsive to change.
Fasting glucose 126+ mg/dL or HbA1c 6.5%+	In the diabetes range. Please talk with your doctor promptly.
Everything in the optimal range	Wonderful. Keep tracking the trend.

How to use these numbers: labs and studies use different cut-offs, and none are agreed on for adults over 50. Share your numbers with your doctor, retest the same markers in 3 to 6 months, and watch which way they move. Your own trend tells you the most.

Thin outside, fat inside

You don't have to be overweight to have insulin resistance. Some people carry fat deep around their organs while their weight looks perfectly normal. BMI can't see where fat sits. Remember, Mrs. D.'s BMI was 22. If you were told you have prediabetes and you're not overweight, this course is still for you.

Speak up for yourself

If your doctor says you don't need a fasting insulin test, it's okay to ask again. Insist upon it, kindly and clearly. It's your body and your data, and you deserve the full picture.

Key idea

Glucose shows the result. Fasting insulin shows the effort. Ask for both, and track them over time.

Try This Week

Use the calculator or worksheet to work out your triglyceride-to-HDL ratio and TyG index.Call your doctor's office and ask to add fasting insulin and hs-CRP to your next blood test.Start a simple log: date, waist, and any lab results. (The worksheet has a tracking log.)

Check your understanding

Sources for this module

NIDDK. Diabetes Tests & Diagnosis. https://www.niddk.nih.gov/health-information/diabetes/overview/tests-diagnosis
NIDDK. Insulin Resistance & Prediabetes. https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/prediabetes-insulin-resistance
Matthews DR, et al. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia. 1985;28(7):412-419.
McLaughlin T, et al. Use of metabolic markers to identify overweight individuals who are insulin resistant. Ann Intern Med. 2003;139(10):802-809.
Zheng Z, et al. TyG index as a biomarker of insulin resistance. Front Pharmacol. 2026;17:1787130.
Ding C, et al. Metabolically obese normal-weight individuals. Am J Physiol Endocrinol Metab. 2018;314(5):E494-E502.
Shoelson SE, Lee J, Goldfine AB. Inflammation and insulin resistance. J Clin Invest. 2006;116(7):1793-1801.
Selvin E, et al. Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults. N Engl J Med. 2010;362(9):800-811.
Gaziano JM, et al. Fasting triglycerides, high-density lipoprotein, and risk of myocardial infarction. Circulation. 1997;96(8):2520-2525.
Tabák AG, Jokela M, Akbaraly TN, et al. Trajectories of glycaemia, insulin sensitivity, and insulin secretion before diagnosis of type 2 diabetes: an analysis from the Whitehall II study. Lancet. 2009;373(9682):2215-2221. doi:10.1016/S0140-6736(09)60619-X. PMID: 19515410.