Hemoglobin A1c (HbA1c)
HbA1c reflects the fraction of hemoglobin with glucose attached and estimates average blood sugar over the prior two to three months. It is the standard test for diagnosing and monitoring diabetes, with values below 5.7 percent considered normal, 5.7 to 6.4 prediabetic, and 6.5 or higher diabetic. Anemia and hemoglobin variants can distort the result.
Units: %; some labs report mmol/mol (mmol/mol = (% − 2.15) × 10.929). Check the units on your report before comparing to any range here.
Optimal range: who says what
Institutions, researchers and practitioners draw the line in different places. Each position is listed with who holds it and, where a document states it, a link. How we verify ranges.
- Institution or study<5.7% normal; 5.7-6.4% prediabetesADA Standards of Care
- Institution or study5.0-5.4% (lowest-risk reference band)ARIC cohort (Selvin et al. 2010, N Engl J Med)Against 5.0-5.4%, values of 5.5-5.9% carried 1.86 times the diabetes risk and 1.23 times the coronary heart disease risk in adults without diabetes
- Named practitioner<5.5%Dr. Mark Hyman · Blood Tests to Ask Your Doctor ForDisclosure: Hyman co-founded Function Health, which appears in our blood-test comparisons.
- Named practitioner4.6-5.3%Chris Kresser · When Your 'Normal' Blood Sugar Isn't Normal (Part 2)
- Named practitioner5.0-5.4%Life Extension · Lab Testing Protocol (Suggested Optimal Ranges)Disclosure: Life Extension sells lab panels that appear in our blood-test comparisons.
- Lab reference intervalNormal: <5.7%, Prediabetes: 5.7-6.4%, Diabetes: ≥6.5%What a lab report flags against. A lab interval is not an optimal target.
Practitioner targets are individual positions, often tighter than guideline ranges. Each was checked against its article before publishing.
21 of 21 itemized panels
Metabolic Health / Glucose
What is Hemoglobin A1c (HbA1c)?
HbA1c (hemoglobin A1c or glycated hemoglobin) measures the percentage of hemoglobin proteins in red blood cells that have glucose molecules attached (glycated). Because red blood cells live ~90-120 days, HbA1c reflects average blood glucose over the past 2-3 months. Unlike fasting glucose (a single snapshot), HbA1c captures long-term glycemic control and is the gold standard for diagnosing and monitoring diabetes. HbA1c ≥6.5% = diabetes; 5.7-6.4% = prediabetes; <5.7% = normal (per ADA guidelines).
The ADA's normal range (below 5.7%) spans real differences in risk. In the ARIC cohort, adults with HbA1c of 5.5-5.9% had 1.86 times the diabetes risk and 1.23 times the coronary heart disease risk of those at 5.0-5.4% (Selvin 2010). A systematic review found 5-year diabetes incidence of 9-25% at 5.5-6.0%, versus under 9% at 5.0-5.5% (Zhang 2010). Lower is not always better: all-cause mortality followed a J-shaped curve in ARIC, and in the Health and Retirement Study it was lowest at 5.4% and rose significantly below 5.0% in adults without diabetes (Li 2019).
HbA1c also reflects glycation, the non-enzymatic binding of glucose to proteins. Among older adults in the Adult Changes in Thought study, higher average glucose over five years was associated with higher dementia risk, including in people without diabetes (hazard ratio 1.18 for an average of 115 versus 100 mg/dL; Crane 2013).
Why HbA1c Matters for Longevity
- Diabetes diagnosis and monitoring: Under ADA criteria, HbA1c of 6.5% or higher (confirmed on repeat testing) indicates diabetes and 5.7-6.4% indicates prediabetes. HbA1c needs no fasting and reflects roughly the past 2-3 months. Treatment goals for people with diabetes are set individually.
- Cardiovascular disease: In ARIC, HbA1c of 6.0-6.4% carried 1.78 times the coronary heart disease risk of 5.0-5.4%, and HbA1c predicted risk better than fasting glucose (Selvin 2010).
- Diabetes prevention: Progression from prediabetes can be slowed. In the Diabetes Prevention Program, a lifestyle program cut progression to diabetes by 58% and metformin by 31% (Knowler 2002).
- Microvascular complications: In people with diabetes, years of high HbA1c drive retinopathy, kidney disease, and neuropathy.
- Cognitive decline: Higher average glucose is associated with higher dementia risk even without diabetes (Crane 2013).
Interpretation bands (curated, PMID-backed)
Holder: OptimizeBiomarkers editorial synthesis of: Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults (Selvin et al., 2010); Glycated Hemoglobin and All-Cause and Cause-Specific Mortality Among Adults With and Without Diabetes (Li et al., 2019); HbA1c and Risks of All-Cause and Cause-Specific Death in Subjects without Known Diabetes: A Dose-Response Meta-Analysis of Prospective Cohort Studies (Zhong et al., 2016). No single paper sets these cutoffs; for attributed targets see who says what.
Lowest-risk band (cohort data)5.0-5.4%▼
- Reference band with the lowest diabetes and coronary risk in ARIC (Selvin 2010)
- In adults without diabetes in the Health and Retirement Study, all-cause mortality was lowest at 5.4% (Li 2019)
High-normal5.5-5.6%▼
- Below the ADA prediabetes cutoff
- In ARIC, 5.5-5.9% carried 1.86 times the diabetes risk of 5.0-5.4%
Low<5.0%▼
- In adults without diabetes, mortality rose below 5.0% in the Health and Retirement Study (Li 2019)
- Very low values can also reflect anemia, blood loss, or overtreatment with diabetes drugs
Prediabetes (ADA)5.7-6.4%▼
- ADA prediabetes range
- 6.5% or higher on repeat testing indicates diabetes
- Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults.
- Glycated Hemoglobin and All-Cause and Cause-Specific Mortality Among Adults With and Without Diabetes.
- HbA1c and Risks of All-Cause and Cause-Specific Death in Subjects without Known Diabetes: A Dose-Response Meta-Analysis of Prospective Cohort Studies.
What raises or lowers Hemoglobin A1c
Causes of high Hemoglobin A1c
- Type 2 diabetes: Insulin resistance + progressive beta cell failure. Caused by obesity, sedentary lifestyle, high-carb diet, genetics. Affects 10-12% of US adults.
- Type 1 diabetes: Autoimmune destruction of pancreatic beta cells. No insulin production. Typically diagnosed in childhood/adolescence but can occur at any age (LADA = latent autoimmune diabetes in adults).
- Prediabetes: Impaired fasting glucose (100-125 mg/dL) or impaired glucose tolerance. HbA1c 5.7-6.4%. Affects 35% of US adults.
- Obesity and metabolic syndrome: Visceral fat drives insulin resistance and hyperglycemia.
- Sedentary lifestyle: Physical inactivity worsens insulin resistance.
- Genetics: Family history of diabetes increases risk. Certain ethnicities (South Asian, Hispanic, African American, Native American) higher risk.
- Gestational diabetes: Develops during pregnancy, resolves postpartum. It raises the risk of type 2 diabetes later in life.
- PCOS: Insulin resistance in 70-80% of PCOS cases contributes to hyperglycemia.
- Medications: Glucocorticoids (prednisone), atypical antipsychotics (olanzapine), protease inhibitors (HIV meds).
- Pancreatic disease: Chronic pancreatitis, pancreatic cancer, cystic fibrosis destroy beta cells.
Causes of low Hemoglobin A1c
- Type 1 diabetes with excessive insulin: Over-treatment causes frequent hypoglycemia, driving HbA1c too low (<4.5%).
- Type 2 diabetes with excessive sulfonylureas or insulin: Risk of hypoglycemia if HbA1c <5.5% while on these medications.
- Hemolytic anemia or rapid RBC turnover: Shortened RBC lifespan means less time for glycation, falsely lowering HbA1c. Check fructosamine or continuous glucose monitoring (CGM).
- Chronic kidney disease: Uremia can interfere with HbA1c assay (usually falsely lowers it).
- Recent blood transfusion: Transfused RBCs haven't been exposed to patient's glucose, falsely lowering HbA1c.
Symptoms when Hemoglobin A1c is high or low
When high
Symptoms of hyperglycemia and diabetes (HbA1c >6.5%):
- Polyuria (frequent urination, especially at night)
- Polydipsia (excessive thirst)
- Polyphagia (increased hunger despite eating)
- Unexplained weight loss (type 1 or advanced type 2)
- Fatigue, low energy
- Blurred vision (glucose-induced lens swelling)
- Slow wound healing
- Frequent infections (yeast infections, UTIs, skin infections)
- Neuropathy: Tingling, numbness in hands/feet
- Erectile dysfunction (men)
HbA1c 5.7-6.4% = prediabetes (often asymptomatic). HbA1c ≥6.5% = diabetes (symptoms develop gradually).
When low
- HbA1c rarely goes too low unless over-treated with insulin or sulfonylureas (causing hypoglycemia).
- Hypoglycemia symptoms (blood glucose <70 mg/dL, can occur if HbA1c driven too low with medications):
- Shakiness, tremors
- Sweating, palpitations
- Hunger, irritability
- Confusion, difficulty concentrating
- Dizziness, weakness
- Blurred vision, headache
- If severe (<50 mg/dL): Seizures, loss of consciousness, death (rare)
HbA1c <4.0% may indicate over-treatment with insulin or sulfonylureas, risking dangerous hypoglycemia. In the ARIC cohort, death from any cause was also higher at the low end of HbA1c (Selvin 2010).
How to move Hemoglobin A1c
Effect sizes (how much something moves the marker) appear only where the paper cited under the item states them. Talk to your clinician before starting or changing any medication or supplement.
Low-Carb or Ketogenic Diet (Most Effective)
- Restrict carbohydrates to <100 g/day (low-carb) or <50 g/day (keto). Eliminates postprandial glucose spikes, lowers average glucose, depletes glycogen stores.
- Evidence: Low-carbohydrate diets lower HbA1c in people with prediabetes and diabetes, with most of the effect in the first 3-6 months. More effective than low-fat diets.
- Focus: Eliminate processed carbs (bread, pasta, rice, sugar, sugary drinks). Prioritize vegetables, protein, healthy fats.
Intermittent Fasting and Time-Restricted Eating
- 16:8 intermittent fasting (fast 16 hours, eat within 8-hour window) or alternate-day fasting lowers average glucose and improves insulin sensitivity.
- Time-restricted eating has lowered HbA1c modestly in some trials in prediabetes.
- Mechanism: Extended fasting depletes liver glycogen, enhances fat oxidation, reduces insulin resistance.
Weight Loss (5-10% Body Weight)
- Even modest weight loss (5-10% of body weight) significantly lowers HbA1c. Larger weight loss brings larger HbA1c reductions.
- Visceral fat loss improves insulin sensitivity and reduces hepatic glucose production.
- Combine calorie deficit with resistance training to preserve muscle mass.
Exercise (Resistance + Aerobic)
- Resistance training: Builds muscle, which is metabolically active and glucose-hungry. Increases GLUT4 receptors, improving glucose uptake. 3-4x/week.
- Aerobic exercise: 150 min/week moderate-intensity (brisk walking, cycling) or 75 min/week vigorous (running, HIIT). Lowers HbA1c.
- Post-meal walks: 10-15 min walk after meals blunts the post-meal glucose rise.
Medications (if HbA1c ≥6.5% or prediabetes not responding to lifestyle)
- Metformin: 1000-2000 mg/day. First-line for type 2 diabetes and prediabetes. Reduces hepatic glucose production, improves insulin sensitivity. Lowers HbA1c.
- GLP-1 agonists (semaglutide, liraglutide): 0.5-2.4 mg/week (injectable). Large HbA1c reductions and weight loss; some agents have shown cardiovascular benefit. Expensive but highly effective.
- SGLT2 inhibitors (empagliflozin, dapagliflozin): 10-25 mg/day. Increase urinary glucose excretion. Lower HbA1c and reduce heart failure and kidney disease events.
- Insulin: Required for type 1 diabetes and advanced type 2. Titrate to the HbA1c goal your clinician sets; the ADA Standards of Care use <7% for many adults with diabetes.
When to retest
- Baseline: Check HbA1c if risk factors for prediabetes/diabetes: overweight/obesity, family history, age >45, PCOS, gestational diabetes history, sedentary lifestyle.
- Annual screening: For everyone ≥45 years old. For younger adults if overweight + 1 risk factor (family history, hypertension, dyslipidemia, PCOS).
- Every 3 months if diabetic: Monitor glycemic control and adjust medications. Your clinician sets the target.
- After lifestyle intervention: Retest 3 months after starting low-carb diet, intermittent fasting, exercise, weight loss.
- If prediabetic (5.7-6.4%): Retest every 6-12 months while implementing lifestyle changes to prevent progression to diabetes.
- No fasting required: HbA1c can be tested any time of day, regardless of meals (major convenience advantage over fasting glucose).
Scientific Evidence
HbA1c and Diabetes Diagnosis
Under American Diabetes Association criteria, an HbA1c of 6.5% or higher is one of the criteria for diagnosing diabetes, and 5.7-6.4% defines prediabetes. Whether HbA1c is an adequate diagnostic tool for prediabetes is still debated, and results can disagree with glucose-based tests.
Source: Definitions (and Current Controversies) of Diabetes and Prediabetes.
HbA1c Predicts Diabetes and Heart Disease
In 11,092 ARIC adults without diabetes, compared with an HbA1c of 5.0-5.4%, values of 5.5-5.9% carried 1.86 times the risk of diagnosed diabetes and 1.23 times the risk of coronary heart disease; 6.0-6.4% carried 4.48 and 1.78 times. Death from any cause followed a J-shaped curve, higher at both ends.
Source: Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults.
HbA1c and Future Diabetes
A systematic review of 16 studies found 5-year diabetes incidence of 25-50% at HbA1c 6.0-6.5% and 9-25% at 5.5-6.0%. Between 5.0% and 5.5% incidence was higher than below 5.0%, but under 9% over 5 years.
Source: A1C level and future risk of diabetes: a systematic review.
Preventing Diabetes in Prediabetes
The Diabetes Prevention Program randomized 3,234 adults with raised glucose to placebo, metformin, or a lifestyle program targeting 7% weight loss and 150 minutes of activity per week. Over 2.8 years, the lifestyle program cut diabetes incidence by 58% and metformin by 31%.
Source: Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin.
Glucose and Dementia Risk
In 2,067 older adults in the Adult Changes in Thought study, higher average glucose over the prior 5 years was associated with higher dementia risk, including in people without diabetes: an average glucose of 115 versus 100 mg/dL carried a hazard ratio of 1.18.
Which Providers Test Hemoglobin A1c (HbA1c)?
Cheapest: Oura Health Panels at $99/year. Most comprehensive: Function Health, 160+ biomarkers for $365/year.
21 panels that include it, cheapest first
| Provider | Annual Cost | Total Biomarkers | $/Biomarker |
|---|---|---|---|
| $99 | 50 | $1.98 | |
| $190 | 100+ | $1.90 | |
| $250 | 65 | $3.85 | |
| $297 | 100+ | $2.97 | |
 Labcorp OnDemand | $338 | 50+ | $6.76 |
 Superpower | $349 | 100+ | $3.49 |
| $349 | 75+ | $4.65 | |
 WHOOP Advanced Labs | $349 | 65 | $5.37 |
 Function Health | $365 | 160+ | $2.28 |
| $365 | 100+ | $3.65 | |
| $375 | 108 | $3.47 | |
| $449 | 83 | $5.41 | |
| $495 | 80+ | $6.19 | |
| $499 | 100+ | $4.99 | |
| $700 | 138 | $5.07 | |
| $829 | 54 | $15.35 | |
| $895 | 100+ | $8.95 | |
| $996 | 59 | $16.88 | |
| $1188 | 70+ | $16.97 | |
| $1198 | 40+ | $29.95 | |
| $1950 | 130+ | $15.00 |
$/Biomarker is annual cost divided by the panel's advertised biomarker count, not the price of this one test. We track 23 blood test providers (32 plans); 21 of those plans are itemized marker by marker. Compare all of them.
11 providers not itemized in our matrix
We have not itemized these marker by marker (some sell tests one at a time), so this page cannot say whether they offer Hemoglobin A1c (HbA1c). Check with them directly.
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Experts discussing Hemoglobin A1c (HbA1c)
Podcast episodes where clinicians and researchers cover this marker in depth. Curated by hand; an episode is listed only when the marker is a substantial topic, not a passing mention.
- Dr. Casey Means: Transform Your Health by Improving Metabolism & Blood Sugar RegulationDisclosure: Huberman Lab has been sponsored by Function Health, which appears in our blood-test comparisons.
- Check These Biomarkers on Your Next Blood Test
- Episode 385: Carnivore Diet and Dr. Baker's Blood Work
- Your Lab Tests Are Normal But You Feel Sick: What Your Doctor Is MissingDisclosure: Hyman co-founded Function Health, which appears in our blood-test comparisons.
- Are You Pre-Diabetic? Know Your NumbersDisclosure: Hyman co-founded Function Health, which appears in our blood-test comparisons.
- How Insulin Resistance Drives Fatty Liver, Cognitive Issues, and Metabolic SyndromeDisclosure: Hyman co-founded Function Health, which appears in our blood-test comparisons.
Frequently Asked Questions
What is the optimal range for Hemoglobin A1c (HbA1c)?
Published positions differ: <5.7% normal; 5.7-6.4% prediabetes (ADA Standards of Care); 5.0-5.4% (lowest-risk reference band) (ARIC cohort (Selvin et al. 2010, N Engl J Med)). Named practitioners target: <5.5% (Dr. Mark Hyman); 4.6-5.3% (Chris Kresser); 5.0-5.4% (Life Extension). Lab reference interval: Normal: <5.7%, Prediabetes: 5.7-6.4%, Diabetes: ≥6.5%. That is what a lab report flags against, not an optimal target.
Which blood test providers include Hemoglobin A1c (HbA1c)?
21 of the 21 blood testing panels we itemize marker by marker include Hemoglobin A1c (HbA1c) in their panels. This biomarker is widely available across major providers.
Related: YouBoost rates lifestyle and supplement interventions by evidence; HRV Zone tracks recovery trends.
Medical Disclaimer
This information is for educational purposes only and is not medical advice. Always consult with a qualified healthcare provider about your specific health needs.
Last reviewed Sep 23, 2026 · First published Sep 30, 2025