The One Lab Test That Catches Metabolic Problems Before Your Doctor Will
By Missy Zammichieli, DNP, APRN, FNP-BC
A lot of patients come to me after their annual physical and say the same thing. “My doctor said everything looks good.” And then I run a full panel and find their fasting insulin is 18, 22, sometimes higher. Their blood sugar is technically normal. Their A1C is fine. But their insulin is working overtime to keep it that way, and nobody told them.
That’s the problem with standard screening. It catches diabetes. It doesn’t catch the 10 to 15 years of metabolic dysfunction that happen before diabetes shows up on a basic lab panel.
What fasting insulin actually tells you
So your body uses insulin to move sugar out of your blood and into your cells. When everything’s working well, it doesn’t take much insulin to do that job. But when your cells start becoming resistant to insulin, usually from excess visceral fat, chronic inflammation, poor sleep, high stress, things like that, your pancreas has to produce more and more insulin to get the same result.
Your blood sugar stays normal because your pancreas is compensating. But the insulin level is climbing. That’s the part your doctor isn’t checking.
By the time blood sugar or A1C actually goes out of range, you’ve likely had insulin resistance for years. I used to think that if someone’s fasting glucose was fine, they were probably fine metabolically. I don’t think that anymore. I’ve seen too many patients with a fasting glucose of 92 and a fasting insulin of 24. That’s not fine. That’s a pancreas running at redline.
What I look for in my practice
I run fasting insulin on almost every patient now, regardless of what their glucose looks like. Here’s what the numbers tell me:
Fasting insulin under 5 is optimal. Between 5 and 8, I’m not worried but I’m watching. Above 10, we’re having a conversation about what’s driving it. Above 15, we’re making changes. And I see a lot of people walking around above 15 who’ve been told they’re healthy because their glucose is 95 and their A1C is 5.4.
I pair this with a full metabolic panel that includes glucose, A1C, and insulin together. Looking at glucose without insulin is like checking the oil light without checking the oil level. The light might not be on yet, but that doesn’t mean you’re not running low.
Why this matters before things go wrong
Insulin resistance doesn’t just lead to diabetes. It’s connected to weight gain that won’t respond to diet and exercise, elevated triglycerides, fatty liver, increased cardiovascular risk, hormonal disruption, things like that. In women, high insulin can drive testosterone up and contribute to PCOS symptoms. In men, it can tank testosterone and accelerate visceral fat storage.
One example I see constantly. A patient comes in frustrated because they’ve been training four or five days a week, eating well, and they can’t lose the belly fat. Their doctor has never checked insulin. We run it, it’s 19. We address the insulin resistance through dietary changes, sometimes medication, and suddenly their body starts responding to the work they’re already putting in.
The difference between optimal and normal lab ranges matters here more than almost anywhere else. A fasting insulin of 14 is “in range” at most labs. It’s not optimal by any stretch, and I’d argue it represents early metabolic dysfunction that should be addressed, not ignored.
What to do with this information
Ask your doctor to add fasting insulin to your next blood draw. It’s inexpensive and most labs can run it. If they push back, that tells you something about how they think about prevention versus disease management.
If your fasting insulin is elevated, the basics matter. Reducing processed carbohydrates, strength training, improving sleep quality, and managing stress all improve insulin sensitivity. But you can’t fix what you don’t measure. And right now, most people have no idea where their insulin sits because nobody’s checking.
I’d rather catch this at a fasting insulin of 14 and make adjustments than wait until someone’s A1C crosses 6.5 and we’re talking about diabetes medication. By that point, the damage has been accumulating for a decade. We should be intervening much earlier. And it starts with running the right test.
Missy Zammichieli, DNP, APRN, FNP-BC, is the Medical Director at Moonshot Medical and Performance in Park Ridge, IL, where she specializes in hormone optimization, metabolic health, and data-driven preventive care.
