There's a gap in standard metabolic screening that affects a significant number of women — and the people most affected usually don't know it exists until something else goes wrong. The test is simple, inexpensive, and available at any standard lab. It just doesn't get ordered.
Here's what fasting insulin actually measures, why the standard reference range is misleading, and what the research says about the window between optimal and flagged.
What Fasting Insulin Actually Measures
Glucose and insulin are not the same number. Most standard metabolic panels include a fasting glucose test — and if that number looks normal, the conversation about metabolic health usually ends there. But glucose is a lagging indicator. By the time it starts to climb, insulin has often been elevated for years.[1]
Here's why: insulin is the hormone your pancreas releases to move glucose from your bloodstream into your cells. When cells become resistant to insulin's signal — a process that develops gradually in response to diet, stress, sleep disruption, and other factors — the pancreas compensates by producing more insulin to achieve the same effect. Blood glucose stays normal. Insulin climbs. And nothing gets flagged.
This state — elevated insulin with normal glucose — is called hyperinsulinemia. It can persist for years before glucose becomes abnormal. A 2023 paper in Frontiers in Clinical Diabetes and Healthcare described it as "an early biomarker of metabolic dysfunction" that precedes type 2 diabetes and is independently associated with cardiovascular disease, cognitive decline, and metabolic syndrome.[2]
Hyperinsulinemia Precedes Glucose Dysregulation by Years
A 5-year longitudinal study published in Cardiovascular Diabetology found that elevated fasting insulin was a significant predictor of future metabolic syndrome — independent of fasting glucose. Participants with high insulin but normal glucose were substantially more likely to develop full metabolic syndrome by the end of the follow-up period than those with low insulin.[1]
Sung KC et al., Cardiovascular Diabetology, 2011The 17-Point Gap
Standard lab reference ranges for fasting insulin typically mark anything below 25 μIU/mL as normal. Some labs use an upper limit of 20 or even 30. The functional medicine community, informed by a growing body of metabolic research, considers optimal fasting insulin to be below 8 μIU/mL — and ideally closer to 5 or 6 in someone with good metabolic health.
That's a gap of 17 points or more between what clinicians consider optimal and what standard labs will flag as abnormal. A person with a fasting insulin of 22 μIU/mL would receive no comment on their lab results — and no follow-up — under most standard screening protocols.
Values in μIU/mL. Standard lab upper limits range from 20–30 depending on the lab. Functional medicine optimal is typically cited as below 8 μIU/mL. The window between the two represents years of potential metabolic drift with no clinical intervention.
Why It Matters Even When You Feel "Fine"
Hyperinsulinemia is largely silent in its early stages. Most people won't notice a number on a panel they've never seen. But the downstream effects of chronically elevated insulin are not invisible — they show up as symptoms that are frequently dismissed, attributed to stress or aging, or left unaddressed.
None of these symptoms will prompt a fasting insulin order on a standard panel. They're non-specific — they fit dozens of diagnoses, or no diagnosis at all. That's exactly the problem. When the most informative early marker isn't being checked, the symptoms that point to it don't connect.
Insulin resistance is a process, not an event. By the time glucose shifts, the metabolic environment that drives it has often been in place for years — visible in a number that was never ordered.
Synthesis of metabolic research literatureWhy This Particularly Affects Women
Women are disproportionately affected by the gap in fasting insulin screening for several reasons. First, PCOS — which affects an estimated 8–13% of women of reproductive age — is strongly associated with insulin resistance, yet insulin levels are not part of standard PCOS diagnostic criteria.[3] Many women with PCOS have been told their metabolic markers look fine because glucose was never abnormal.
Second, the hormonal shifts of perimenopause substantially alter insulin sensitivity. Declining estrogen affects how cells respond to insulin signaling, making the perimenopausal window a particularly high-risk period for developing insulin resistance — and a period when metabolic screening is rarely updated to reflect that increased risk.[4]
Research published in the Journal of Clinical Endocrinology & Metabolism found that insulin sensitivity declines significantly during the menopause transition — independent of changes in body weight. Women moving through perimenopause who have never had metabolic concerns may find their insulin picture changing without any corresponding change in fasting glucose.[4]
How to Get This Number
Fasting insulin is not an exotic test. It's available at every standard lab — Quest, LabCorp, and most hospital systems offer it. The challenge is simply getting it ordered.
Most primary care physicians won't add it without a specific request, because it isn't part of standard metabolic panel protocols. Functional medicine practitioners routinely include it. Direct-to-consumer lab services also offer it, typically for under $30, without a physician order.
- Fasting insulin — specify this by name, as it won't appear on a standard CMP or BMP
- Fasting glucose — for context alongside the insulin number
- HOMA-IR — a calculated ratio derived from fasting insulin and glucose that estimates insulin resistance severity
- Hemoglobin A1c — a 90-day average of blood sugar that captures glucose trends over time
- Triglycerides — often elevated in hyperinsulinemia even when other markers look normal
The combination of fasting insulin, fasting glucose, and HOMA-IR gives a far more complete picture of metabolic function than glucose alone. If you've been told your metabolic health looks fine but still feel off, this set of markers is worth the conversation.
The Bottom Line
Standard screening is designed to catch disease — not to optimize function or catch the early conditions that precede it. Fasting insulin sits in the gap between the two: a well-validated, inexpensive marker that tells you something meaningful about metabolic health years before anything gets flagged.
The gap between optimal and "normal" is 17 points. That's a long window where nothing gets said and nothing gets done. Knowing the number doesn't guarantee intervention — but it does give you something to work with. And most people who ask for this test have never been offered one.
References
- 1Sung KC et al. Elevated fasting insulin predicts the future incidence of metabolic syndrome: a 5-year follow-up study. Cardiovascular Diabetology. 2011;10:108. doi:10.1186/1475-2840-10-108
- 2Vaidya RA et al. Hyperinsulinemia: an early biomarker of metabolic dysfunction. Frontiers in Clinical Diabetes and Healthcare. 2023;4:1159664. doi:10.3389/fcdhc.2023.1159664
- 3Bozdag G et al. The prevalence and phenotypic features of polycystic ovary syndrome: a systematic review and meta-analysis. Human Reproduction. 2016;31(12):2841–2855. PMID: 27664216
- 4Mauvais-Jarvis F et al. The role of estrogens in control of energy balance and glucose homeostasis. Endocrine Reviews. 2013;34(3):309–338. PMID: 23460719
- 5Zhang X et al. Fasting insulin, insulin resistance, and risk of cardiovascular or all-cause mortality in non-diabetic adults: a meta-analysis. Bioscience Reports. 2017;37(5). doi:10.1042/BSR20170947
- 6Reaven GM. Banting Lecture 1988. Role of insulin resistance in human disease. Diabetes. 1988;37(12):1595–1607. Foundational paper establishing insulin resistance as an independent cardiovascular and metabolic risk factor. PMID: 3056758
This article is for educational and informational purposes only. Nothing in this article constitutes medical advice, a diagnosis, or a treatment recommendation. Always consult a qualified healthcare provider before requesting specific tests or making changes to your health protocol. BioRefined does not diagnose, treat, or prescribe.