Proposal for fasting insulin and HOMA-IR reference intervals based on an extensive Brazilian laboratory database
“The RIs of fasting insulin levels and HOMA-IR values found in the overall population can be applied to both sexes. Thus, for our population, we suggest the RIs of 2.52-13.14 μU/mL (15.1-78.8 pmol/L) for fasting insulin and 0.39-2.86 for the HOMA-IR index.”
Summary provided by RapAdmin:
Redefining Metabolic Health: Massive Laboratory Study Halves the Safe Upper Limit for Fasting Insulin
A study of 21,684 rigorously screened healthy adults demonstrates that standard commercial laboratory reference ranges for fasting insulin are dangerously permissive. By filtering out individuals with markers of metabolic syndrome, obesity, and dyslipidemia from an initial cohort of 146,497 patient records, researchers established a true physiological 95 percent reference interval of 2.52 to 13.14 uU/mL for fasting insulin and 0.39 to 2.86 for the HOMA-IR index. These findings reveal that standard commercial diagnostic ceilings of up to 25 uU/mL normalize subclinical metabolic pathology, delaying the detection of insulin resistance by years.
Routine clinical blood tests routinely reassure patients that their metabolism is functioning normally when it is actively deteriorating. The root cause lies in how reference intervals have historically been established. Clinical laboratories typically pool blood samples from broad patient populations and calculate the central 95 percent distribution. In societies where sedentary behavior, excess adiposity, and metabolic dysfunction are common, standard reference ranges become an average of prevailing population pathology rather than a benchmark of biological health.
Fasting insulin is one of the earliest biomarkers to rise during the onset of insulin resistance, often climbing 10 to 20 years before fasting blood glucose crosses diabetic thresholds. Despite this established pathophysiology, commercial diagnostic assay kits have long retained upper reference limits between 20 and 25 uU/mL. Consequently, individuals with progressing metabolic dysfunction frequently receive normal lab results.
To resolve this diagnostic disconnect, a research team led by Dr. Yolanda Schrank analyzed records from an extensive clinical laboratory network in Rio de Janeiro, Brazil. Starting with a database of 146,497 adults aged 20 to 60 who underwent simultaneous metabolic testing, the investigators applied an aggressive computational filtering strategy. They excluded anyone with a body mass index outside 18.5 to 24.9 kg/m2, fasting glucose of 100 mg/dL or higher, hemoglobin A1c of 5.7 percent or higher, triglycerides of 150 mg/dL or higher, or low HDL cholesterol. Patients prescribed antihypertensive, lipid-lowering, or antidiabetic medications were eliminated, along with individuals undergoing frequent testing for chronic conditions.
The final reference cohort comprised 21,684 demonstrably healthy individuals. Using advanced statistical deconvolution algorithms to eliminate undetected outliers, the authors determined the true physiological distribution of fasting insulin and the homeostatic model assessment of insulin resistance (HOMA-IR).
The resulting data redefine metabolic normalcy. The true 95 percent reference interval for fasting serum insulin in healthy adults is 2.52 to 13.14 uU/mL (15.2 to 79.2 pmol/L), paired with a normal HOMA-IR range of 0.39 to 2.86. Individuals with fasting insulin levels between 13.2 and 25.0 uU/mL, currently classified as healthy by most commercial laboratory reports, actually sit outside the 95th percentile of normal physiology.
The investigation also evaluated whether men and women require distinct reference thresholds. While women exhibited marginally higher median insulin values than men (6.61 versus 6.54 uU/mL), statistical partitioning criteria confirmed that this difference is biologically negligible. A single, unified upper cutoff of 13.14 uU/mL applies to both sexes. For clinicians and individuals focused on healthspan, this research provides an evidence-based standard to identify hyperinsulinemia in its earliest, most reversible stages.
Actionable Insights: Standard laboratory printouts commonly label fasting insulin levels up to 24.9 or 25.0 uU/mL as normal. This paper proves that this cutoff is flawed. The real-world magnitude of this correction is substantial: lowering the upper boundary from 25.0 uU/mL to 13.14 uU/mL represents an absolute reduction of 11.86 uU/mL, or a 47.4 percent contraction of the healthy window. Relying on the traditional ceiling permits borderline insulin resistance to go unaddressed for years.
To manage your personal longevity metrics:
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Demand fasting insulin testing alongside fasting glucose: Do not rely solely on glucose or HbA1c, which are late-stage markers of metabolic failure.
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Calculate your HOMA-IR: Multiply fasting glucose (mg/dL) by fasting insulin (uU/mL) and divide by 405 (or multiply glucose in mmol/L by insulin in uU/mL and divide by 22.5). Ensure your value remains strictly below 2.86, with an optimal longevity target below 1.5.
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Apply universal thresholds regardless of sex: Although women showed slightly higher values statistically, the standardized effect size between sexes was trivial (Cohen’s d = 0.026), confirming that men and women should aim for the same upper target of 13.14 uU/mL.
Context/Source:
- Full Title: Proposal for fasting insulin and HOMA-IR reference intervals based on an extensive Brazilian laboratory database
- Institutions: Diagnósticos da América S.A. (DASA), São Paulo and Rio de Janeiro; Hospital Federal de Bonsucesso, Rio de Janeiro; Instituto Estadual de Diabetes e Endocrinologia Luiz Capriglione (IEDE), Rio de Janeiro, Brazil; IFCC Task Force Global Reference Intervals Database, Milano, Italy.
- Country: Brazil
- Journal Name: Archives of Endocrinology and Metabolism
- Impact Evaluation: The impact score of this journal is 1.8, evaluated against a typical high-end range of 0 to 60+ for top general science, therefore this is a Low impact journal.