How to Test for Insulin Resistance. What to Ask For and What the Numbers Mean.

The Insulin Resistance Atherosclerosis Study (IRAS) found that fasting insulin was the strongest single predictor of type 2 diabetes onset in the prediabetic window, outperforming fasting glucose even in people who would go on to develop the disease (Haffner et al., Arch Intern Med, 1997). The standard lab panel your doctor orders does not include fasting insulin. This is a gap with consequences.

Fasting glucose appears on every standard metabolic panel. It measures the result of insulin’s work. What it does not measure is whether insulin is working harder than it should be to maintain that result. A man with a fasting glucose of 90 can be in the middle of an active insulin resistance process and have no idea, because the number looks clean. His pancreas is compensating for tissue resistance by producing more insulin, and the compensation is holding. For now.

The test that reveals this is fasting insulin. Here is what it measures, why it matters to your heart, how to get it, and how to read the result.

The Mechanism

To understand why fasting glucose misses insulin resistance, you need to understand what happens during the compensated phase.

Insulin resistance begins at the level of muscle, liver, and fat cells. These cells start responding less efficiently to insulin signals. Glucose uptake slows. The pancreatic beta cells detect elevated blood glucose and respond by producing more insulin to force the job through. In a person with healthy beta cell reserve, this compensation works. Blood glucose returns to the normal range. Fasting glucose the next morning looks fine.

This compensated state can persist for five to ten years. During this entire window, fasting glucose may remain below 100 mg/dL. It reads as normal on the standard panel. Meanwhile, insulin levels are elevated, and that elevation is doing measurable damage.

Chronically elevated insulin drives a specific set of physiological changes that matter for cardiovascular risk. First, insulin promotes sodium retention in the kidney, which raises blood pressure. Second, hyperinsulinemia stimulates the liver to overproduce very low-density lipoprotein (VLDL), which translates to elevated triglycerides and an atherogenic lipid pattern even when LDL cholesterol appears normal. Third, high insulin promotes visceral fat storage, particularly around the abdomen and the organs, which sustains the resistance in a reinforcing cycle. Fourth, elevated insulin increases low-grade systemic inflammation, raising C-reactive protein.

The compensation eventually fails. Beta cells that have been producing excess insulin for years accumulate stress. Their capacity declines. When compensation starts to break down, fasting glucose begins to rise, HbA1c climbs, and the diagnosis of prediabetes or type 2 diabetes follows. By that point, the atherogenic process has been running for years. The glucose number finally became abnormal, but the vascular clock started ticking long before.

Fasting insulin catches the compensation phase directly. It does not wait for the compensation to fail. A man with fasting glucose of 92 and fasting insulin of 18 uIU/mL has a very different metabolic picture than a man with the same glucose and a fasting insulin of 5. Fasting glucose cannot make that distinction. Fasting insulin can.

What the Evidence Shows

The cardiovascular implications of hyperinsulinemia were established before the specific insulin resistance tests became widely discussed.

The Helsinki Policemen Study (Pyorala et al.) followed men over 22 years and found that men in the highest fasting insulin quartile had a 2.2-fold greater cardiovascular event rate compared to those in the lowest quartile, independent of blood pressure, lipids, smoking, and body weight. The elevated insulin came before the cardiovascular events. It was not a marker of existing disease. It was a precursor. 4 / Promising

The IRAS study (Haffner et al., Arch Intern Med, 1997) specifically examined which early measures predicted progression to type 2 diabetes. Fasting insulin predicted it better than fasting glucose in the prediabetic window, because it was measuring the mechanism rather than the downstream result. 4 / Promising

The triglyceride-to-HDL ratio as a proxy for insulin resistance was examined by McLaughlin et al. (J Clin Endocrinol Metab, 2003), who found it correlated with insulin sensitivity measured by gold-standard clamp studies. Gaziano et al. (Circulation, 1997) showed that a high triglyceride-to-HDL ratio was independently associated with myocardial infarction risk. A ratio above 3.0 in mg/dL units, or above 1.5 in mmol/L, should prompt testing for insulin resistance. 3 / Early

The mechanism connecting hyperinsulinemia to ApoB is direct. Insulin normally suppresses hepatic VLDL production. When cells become insulin resistant, this suppression fails. The liver continues overproducing VLDL regardless of insulin signaling. The result is elevated triglycerides, low HDL, and an increase in small dense LDL particles, all of which raise ApoB. This is why a man can have an LDL of 100 mg/dL, which looks acceptable, while carrying an ApoB load that reflects substantially more atherogenic particle burden. Fasting insulin is part of interpreting that discordance. 4 / Promising

For the oral glucose tolerance test: adding insulin measurements at 30 and 120 minutes reveals postprandial hyperinsulinemia before fasting values change. A man who has normal fasting insulin but whose insulin spikes to 150 uIU/mL at 30 minutes and remains elevated at 120 minutes has established insulin resistance that is not visible in a fasting draw. The 2-hour OGTT with insulin is not commonly ordered but is available at most reference labs and provides the most complete staging of the process. This level of testing is most relevant for men with strong family history, significant central obesity, or discordant results from other tests. 4 / Promising

The Tests, What They Measure, and How to Read Them

Fasting insulin. This is the most clinically useful single addition to standard metabolic testing for a man who believes he is metabolically fine and has a normal fasting glucose.

The standard reference range on most US lab reports extends to 25 uIU/mL. This range reflects where the general population falls, not where metabolic health sits. Below 7 uIU/mL represents good insulin sensitivity in a metabolically healthy person. Between 7 and 10 is borderline, worth monitoring and worth addressing behavioral inputs. Above 10 with normal fasting glucose indicates active compensated resistance. Above 15 is consistent with established moderate-to-severe resistance. Above 25 indicates severe resistance and is often accompanied by other metabolic abnormalities.

The test requires an overnight fast of at least 8 hours. It is drawn from the same blood tube as any standard morning lab. No additional preparation is needed beyond the standard fasting requirement. 4 / Promising

HOMA-IR (Homeostatic Model Assessment of Insulin Resistance). HOMA-IR is calculated from two values you may already have or can get in a single fasting draw: fasting insulin and fasting glucose.

The formula:

If glucose is in mmol/L: HOMA-IR = (Fasting Insulin in uIU/mL x Fasting Glucose in mmol/L) / 22.5

If glucose is in mg/dL: HOMA-IR = (Fasting Insulin in uIU/mL x Fasting Glucose in mg/dL) / 405

A HOMA-IR above 1.9 is generally considered borderline. Above 2.9 is consistent with significant insulin resistance. Above 5.0 is consistent with severe resistance or overt metabolic syndrome. You can calculate this yourself with any calculator. 4 / Promising

HbA1c with fasting glucose. These two tests together reveal pattern discordance that neither alone captures. A fasting glucose of 92 mg/dL looks normal. An HbA1c of 5.8% looks borderline but not alarming. Together they indicate that the 90-day average blood glucose is higher than the single fasting draw suggests, meaning postprandial glucose regulation is deteriorating even while fasting values appear controlled. In a man with these values plus a fasting insulin above 12, the case for intervention is clear. 4 / Promising

Triglyceride-to-HDL ratio. This is available from any standard lipid panel you already have. Divide your fasting triglycerides by your HDL cholesterol, both in the same units (mg/dL for most US labs). A ratio above 3.0 in mg/dL is associated with insulin resistance in population data (McLaughlin et al., JCEM, 2003; Gaziano et al., Circulation, 1997). It is not a substitute for fasting insulin but is the most accessible first signal that insulin testing is warranted. A man with a triglyceride-to-HDL ratio of 4.2 and a fasting glucose of 94 should be getting fasting insulin. 3 / Early

Oral glucose tolerance test with insulin measurements. The OGTT with insulin levels drawn at fasting, 30 minutes, and 120 minutes post-glucose load is the most complete staging tool available outside of research settings. It reveals postprandial hyperinsulinemia before fasting values rise, which is an earlier signal. It requires 2 hours in a lab, is less convenient, and is not the starting point for most men. It is the appropriate next step when fasting values are borderline or discordant results from other tests suggest the fasting draw is undercalling the problem. 4 / Promising

Interpretation Table

A man with a fasting insulin of 18 and a HOMA-IR of 3.6 is not prediabetic by fasting glucose criteria. He may have a fasting glucose of 91. The compensation is working. What this number tells him is that his pancreas is producing roughly three times the insulin it should need to maintain that glucose level, and that the downstream effects of that excess insulin are already in motion.

How to Order These Tests

Through your physician. The two-sentence script: “I want to add fasting insulin to my morning labs. My triglycerides are [X] and I want to understand whether my glucose regulation pattern has changed.”

If the physician asks for context: “I understand fasting glucose can be normal for years while insulin resistance is developing. Fasting insulin and HOMA-IR catch it earlier, and I want the full picture.”

Most physicians will comply. Fasting insulin is a standard reference laboratory test, not an unusual request. It is the omission from the standard panel that is unusual, not the test itself.

If your physician declines and you want the information: order it directly.

Without a physician. Fasting insulin is available through direct-to-consumer lab access in most US states without a physician order.

Quest Diagnostics offers Insulin, Fasting (test code 30765) through its consumer platform at approximately $20 to $25. LabCorp offers fasting insulin through its Labcorp Patient platform at approximately $15 to $20. Function Health includes fasting insulin and fasting glucose together in its baseline metabolic panel. Rupa Health and Marek Health also provide access.

Total cost for fasting glucose plus fasting insulin together through a DTC platform is typically $30 to $50. You can calculate HOMA-IR yourself from the results. Bring the calculation to your next physician visit with the raw lab values.

The waist circumference signal. Before you order any labs, measure your waist at the level of your navel, relaxed, after exhaling. Above 40 inches in a man is a reliable physical sign of visceral adiposity and a strong prompt to get fasting insulin. It is not a diagnostic criterion, but it is the most accessible free screening signal available and it takes 20 seconds.

What to Do This Week

1. Pull your most recent lipid panel and calculate your triglyceride-to-HDL ratio. Divide fasting triglycerides by HDL cholesterol. If the result is above 3.0 in mg/dL, put fasting insulin on the list for your next lab draw.

2. Find your most recent HbA1c if one was ordered. If it is 5.5 or above with a fasting glucose below 100, the pattern is worth investigating with fasting insulin. The two numbers are telling different parts of the same story.

3. At your next morning lab draw, ask your physician to add fasting insulin. The test requires the same fasting prep and the same blood draw as any standard morning metabolic panel. One additional tube. The words to use: “I want fasting insulin added to my labs today.”

4. If you prefer not to wait for a physician visit, order fasting insulin and fasting glucose through Quest or LabCorp directly. Calculate HOMA-IR from the formula above. A result above 2.9 is worth a direct conversation with your physician.

5. If your HOMA-IR comes back above 3.0, ask your physician about ApoB. A man with established insulin resistance who is relying on LDL alone to assess cardiovascular risk is missing the atherogenic particle load driven by excess hepatic VLDL production. ApoB gives the actual count.

The standard metabolic panel was designed to detect disease. Insulin resistance in the compensated phase is not yet disease by most formal diagnostic criteria. It is the process that precedes the disease by years. The test that detects the process requires asking. That is the only barrier between you and knowing.

The Signal Check is fifteen questions mapping the cardiovascular risk pattern across the physiological domains most commonly missed in standard screenings. It produces a specific starting point for your next clinical conversation.