Posted on March 13, 2025 - 3:32 am by Ali Chappell

How to Ask Your Doctor to Test Your Insulin Levels

Most doctors don’t routinely test insulin levels, which is why insulin resistance often goes undiagnosed for years—even decades. Instead, they focus on blood sugar and A1c, which only tell part of the story. Your blood sugar could be completely normal while your insulin is sky-high, silently driving weight gain, hormone imbalances, and chronic disease.

If you suspect insulin resistance, getting your fasting insulin tested is one of the most valuable things you can do for your health. C-peptide can also be tested as an additional marker of insulin production. But since most doctors aren’t in the habit of ordering these tests, you may need to ask for them directly. Here’s how to approach the conversation with confidence.

Why Doctors Don’t Usually Test Insulin

Many healthcare providers overlook insulin and c-peptide testing for a few reasons:

It’s not part of standard practice guidelines. Historically, insulin measurements varied widely between labs, making results unreliable. Thankfully, testing has improved and is now much more consistent, but many doctors still don’t include insulin in routine lab work.
They rely on blood sugar and A1c. Since diabetes is diagnosed based on high blood sugar, many doctors don’t think to check insulin, even though insulin resistance starts long before blood sugar rises.
They weren’t trained to detect insulin resistance early. Medical education has historically focused on treating type 2 diabetes after it develops, rather than identifying and addressing insulin resistance beforehand. They may not know how to interpret the results.
Insurance doesn’t always cover it. Some providers hesitate to order tests they think won’t be reimbursed, even though fasting insulin and c-peptide are simple and relatively inexpensive tests.

This is why being proactive and requesting the test yourself is so important.

How to Ask for an Insulin Test

When talking to your doctor, here’s a straightforward way to make the request:

“I’d like to check my fasting insulin levels to assess my metabolic health. I understand that blood sugar and A1c don’t always show the full picture, and I want to catch any signs of insulin resistance early. Could you order a fasting insulin test for me?”

For a more comprehensive look at how your body is handling glucose and insulin, ask for a 1-hour or 2-hour insulin test with an oral glucose tolerance test (OGTT):

“I’d like to check both fasting insulin and how my body responds to glucose. Could we do an oral glucose tolerance test with insulin measurements at fasting and 2-hours post-glucose?”

This test provides a clearer picture of how your body is processing sugar and whether you are overproducing insulin in response to a glucose load, which is very common in patients with PCOS.

Understanding Insulin and C-Peptide Tests

There are different ways to measure insulin function, and each test provides unique insights into metabolic health.

Fasting Insulin

Measures the amount of insulin in your blood after an overnight fast.
Helps assess baseline insulin levels and detect early insulin resistance.
Ideal fasting insulin should be below 8 mIU/mL.
Can sometimes be normal in young individuals, even if they are insulin resistant. This is because the liver is able to clear the insulin out of the blood overnight. If this is the case, an oral glucose tolerance test with insulin should be performed.

Oral Glucose Tolerance Test with Insulin

Measures insulin levels before and 1 or 2 hours after consuming a glucose drink.
Helps determine how much insulin your body secretes in response to sugar.
A normal 2-hour insulin level should be below 50 mIU/mL.
High levels suggest hyperinsulinemia, a sign of insulin resistance that often develops long before blood sugar rises. It is very common for patients with PCOS to have high insulin levels after consuming the glucose drink.
Since this test requires more time and preparation, it’s best reserved as a secondary option if fasting insulin doesn’t provide clear answers.

C-Peptide

A marker of how much insulin your body is making.
It is not cleared by the liver, making it a useful test for younger patients who may have normal fasting insulin levels but still be insulin resistant.
Is more expensive to test and cannot be tested using at-home kits.

Most doctors only check blood sugar and A1c, which don’t reveal insulin resistance in its early stages. By testing insulin, you can catch metabolic dysfunction years before blood sugar becomes a problem.

What to Do If Your Doctor Refuses

If your doctor pushes back, try these responses:

“I understand that this isn’t a standard test, but I’d still like to check my fasting insulin for my own knowledge. Can we add it to my routine labs?”
“I know blood sugar and A1c are important, but I also want to see what my insulin levels are. Since insulin resistance can develop long before blood sugar rises, I’d like to be proactive.”
“I’d be happy to pay out of pocket if insurance doesn’t cover it. I just want to get a better understanding of my metabolic health.”

If your doctor still refuses, find a new doctor. You can purchase this test online through Quest Diagnostics or by purchasing a Lilli Metabolic Testing Kit.

How to Interpret Your Insulin Results

One of the biggest challenges of getting an insulin test is that most doctors don’t know how to interpret the results properly. There is no standardized reference range for insulin, and some labs consider levels as high as 30 mIU/mL to be “normal”—which is outrageously high.

For optimal metabolic health:

Fasting insulin should be below 8 mIU/mL (ideally between 3-8 mIU/mL).
A 2-hour insulin should be below 50 mIU/mL.

If your doctor doesn’t know how to interpret the results, that’s okay! You can enter your test results into the Lilli App for a full interpretation and to track changes over time.

How Often Should I Be Testing?

When starting a Low Insulin Lifestyle, you may want to test your insulin levels every other month until they normalize. This helps you track your progress and see how your lifestyle changes are impacting your insulin resistance.

Once your levels are in the normal range (fasting insulin below 8 mIU/mL and 2-hour insulin below 50 mIU/mL), it’s a good idea to continue monitoring at least once a year. Insulin resistance can creep back over time, especially with age, changes in diet, stress, or activity levels, so occasional testing ensures you stay on top of your metabolic health.

The Bottom Line

Asking your doctor to test your insulin is one of the most proactive things you can do for your health. Since insulin resistance often goes undetected until blood sugar rises, catching it early allows you to take action before serious health issues develop. If your doctor is unfamiliar with insulin testing or hesitant to order it, don’t be afraid to advocate for yourself or seek out independent testing options. Your metabolic health is worth it!