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Longevity Library · Lab reference

Written by Daniel Tagge, MD
Updated October 7, 2026
Reviewed October 10, 2026
22 sources · Measured in %

System: Metabolism & Metabolomics

Hemoglobin A1cHbA1c · A1C · Glycated hemoglobin · Glycohemoglobin

In the long cohorts, adults whose hemoglobin A1c sat between 5.0 and about 5.4 percent had the lowest risk of later diabetes and coronary disease; risk rose step by step from 5.5 upward, well inside the laboratory's normal range, and below 5.0 all-cause mortality was higher rather than lower. No trial has tested a target inside the normal range.

Hemoglobin A1c is the share of your hemoglobin that has glucose attached, a weighted average of blood sugar over about three months. Laboratories call anything under 5.7 percent normal. The cohorts put the lowest-risk group at 5.0 to about 5.4, show diabetes and heart risk climbing from 5.5, and find a puzzling excess of deaths below 5.0.

01 · The scale

Where the laboratory range and the evidence sit.

Risk of later diabetes and of coronary disease rose step by step from about 5.5 percent upward in long cohorts, with 5.0 to under 5.5 as the low-risk reference group. Below 5.0, all-cause mortality was higher, not lower, in the same cohorts. No trial has tested a target inside the normal range.

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  1. Common laboratory reference range

    4 to 5.6 % · Typical US laboratories; ADA 2025

  2. Prediabetes

    5.7 to 6.4 % · ADA 2025

  3. Diabetes, on two abnormal results

    6.5 and above % · ADA 2025

  4. Higher all-cause mortality below 5.0 in cohorts

    4 to 4.9 % · Selvin 2010; Cavero-Redondo 2017

  5. Reference group with the lowest diabetes and coronary risk

    5 to 5.4 % · Selvin 2010; Zhang 2010

  6. Diabetes incidence 9 to 25 percent over five years; coronary risk 23 percent higher

    5.5 to 5.9 % · Zhang 2010; Selvin 2010

  7. Diabetes incidence 25 to 50 percent over five years; coronary risk 78 percent higher

    6 to 6.4 % · Zhang 2010; Selvin 2010

  8. Treatment goal for many adults with diabetes: under 7

    6.5 and above % · ADA 2025; KDIGO 2022

  • Laboratory range
  • Evidence supports
  • Guideline goal or unstudied
  • Higher risk in studies
Scale in %. US laboratories report A1c as a percentage of hemoglobin (NGSP units). Many other countries report IFCC units: mmol/mol = (percent minus 2.15) x 10.929, so 5.4 percent is about 36 mmol/mol, 5.7 is about 39 and 6.5 is 48. Bands show where studies found something, not a recommendation for any one person.

02 · What it is

What Hemoglobin A1c measures.

Glucose attaches to hemoglobin inside red blood cells for as long as the cell lives, so the percentage of glycated hemoglobin tracks average blood glucose over the preceding three months. In 507 people measured with continuous monitoring and seven-point fingerstick profiles for three months, average glucose in mg/dL was about 28.7 x A1c minus 46.7, which makes a 5.4 percent A1c roughly 108 mg/dL, a 5.7 roughly 117 and a 6.5 roughly 140.1Grade B

The American Diabetes Association uses A1c to diagnose: 6.5 percent or higher is diabetes, 5.7 to 6.4 is prediabetes, and the test must be run on an assay certified by the National Glycohemoglobin Standardization Program. Without unmistakable high blood sugar, a diagnosis requires two abnormal results, from two tests or from one test on two occasions.2Grade A

A1c is a red-cell measurement as much as a glucose one. In a labeling study of 6 people with diabetes and 6 without, the mean age of circulating red cells ranged from 38 to 60 days among the healthy controls, enough to produce clinically important differences in A1c at the same average glucose. Genetic analysis finds the same thing at population scale: variants that change red-cell indices move A1c independently of glucose.3,4Grade B

03 · The laboratory range

What a laboratory calls normal.

About 4.0 to 5.6 percent, with 5.7 to 6.4 flagged as prediabetes and 6.5 or higher as diabetes, on an NGSP-certified assay.

Unlike most laboratory ranges, the upper limit printed for A1c is not a statistical interval drawn from healthy people. It is the American Diabetes Association's prediabetes threshold of 5.7 percent, chosen as a risk cutoff, and the diabetes threshold of 6.5 percent above it.2Grade A

The normal distribution shifts upward with age. In 2,473 Framingham Offspring and 3,270 NHANES participants without diabetes, A1c rose by about 0.010 to 0.014 percentage points per year, and the 97.5th percentile moved from 5.6 percent (NHANES) and 6.0 percent (Framingham) in people under 40 to 6.2 and 6.6 in people 70 and older. The shift persisted after excluding anyone with impaired fasting or post-load glucose, so it is not explained by hidden prediabetes.5Grade C

A1c is one of the steadier blood tests. When 685 NHANES III participants without diagnosed diabetes were retested about two weeks later, the within-person variation was 3.6 percent for A1c, against 5.7 percent for fasting glucose and 16.7 percent for the two-hour glucose tolerance value. At an A1c of 5.5 that is about 0.2 percentage points of noise, so a one-tenth change between draws is not a change in you.6Grade B

04 · The evidence

What the studies support.

In 11,092 Black and white adults without diabetes or cardiovascular disease in the Atherosclerosis Risk in Communities study, measured in 1990 to 1992 and followed for a median of about 14 years, the hazard of diagnosed diabetes compared with an A1c of 5.0 to under 5.5 was 0.52 below 5.0, 1.86 at 5.5 to under 6.0, 4.48 at 6.0 to under 6.5 and 16.47 at 6.5 or higher. For coronary heart disease the corresponding hazards were 0.96, 1.23, 1.78 and 1.95, with stroke similar, all after adjustment for the usual risk factors and still significant after adjusting for fasting glucose. These are associations in a cohort, not proof that the A1c itself causes the events.7Grade B

Death from any cause followed a J-shaped curve in the same cohort: people below 5.0 percent had a significantly higher risk of dying than those at 5.0 to under 5.5, and the excess persisted after excluding people with anemia, adjusting for hematocrit and red-cell volume, and dropping deaths in the first three years. The authors call for study of the low-normal state and of non-glucose determinants of A1c.7Grade B

A systematic review of 16 studies found annual diabetes incidence ranging from 0.1 percent at an A1c under 5.0 to 54.1 percent at 6.1 or higher. Across the seven studies with fine categories, five-year incidence was under 9 percent at 5.0 to 5.5, 9 to 25 percent at 5.5 to 6.0, and 25 to 50 percent at 6.0 to 6.5, rising steeply across the whole span from 5.0 to 6.5.8Grade B

In the EPIC-Norfolk cohort of 4,662 men and 5,570 women aged 45 to 79, followed from 1995 to 1997 until 2003, the relationship between A1c and both cardiovascular events (806) and deaths (521) was continuous through the whole distribution, with the lowest rates below 5 percent. Each percentage point of A1c carried a relative risk of death of 1.24 in men and 1.28 in women, and 1.26 after excluding anyone with known diabetes, an A1c of 7 or more, or prior cardiovascular disease. Seventy-two percent of the deaths occurred in people with an A1c between 5 and 6.9, not in the 4 percent of the sample with diabetes.9Grade B

Pooling individual records from 73 prospective studies and 294,998 people without known diabetes or cardiovascular disease, followed for a median of 9.9 years with 20,840 cardiovascular events, the Emerging Risk Factors Collaboration also found an approximately J-shaped association between A1c and cardiovascular risk after adjustment for conventional risk factors. Adding A1c to a model that already held those risk factors improved its discrimination only slightly (C-index change 0.0018), so A1c describes risk rather than reclassifying it.10Grade A

A meta-analysis of 46 observational studies reached the same shape from the other direction: among people without diabetes, all-cause mortality was 74 percent higher above 6.0 percent and 19 percent higher below 5.0 than in the middle, and the authors placed the lowest-mortality span at 5.0 to 6.0. In people with diabetes the corresponding span was 6.0 to 8.0.11Grade B

The eye and kidney damage that defined the diagnostic cutoffs rises without a threshold. In 11,357 ARIC participants followed for a median of 14 years, an A1c of 5.7 to 6.4 carried a hazard of chronic kidney disease of 1.12 and 6.5 or higher 1.39, compared with under 5.7, with odds of moderate or severe retinopathy of 1.42 and 2.91. The investigators tested formally for thresholds and found none.12Grade B

Genetics argues that part of the association is causal. Using 50 A1c-associated variants against 60,801 coronary cases and 123,504 controls, replicated in 18,915 cases and 455,971 controls from UK Biobank, each genetically determined percentage point of A1c carried 1.61 times the odds of coronary disease. The variants that act through glucose carried 2.23 times the odds; the variants that act through red cells carried 1.30 times, so even the non-glucose part of A1c tracked heart risk.4Grade B

05 · What moves it

The levers with evidence behind them.

What is listed here has been tested. The size of each effect, and the size of the study, are in the sentence, so a small effect reads as a small effect.

  • A structured lifestyle program

    lowers the chance of progressing to diabetes

    In the Diabetes Prevention Program, 3,234 adults with elevated fasting and post-load glucose (mean body mass index 34) were randomized to placebo, a glucose-lowering medication, or a lifestyle program aiming at 7 percent weight loss and 150 minutes of activity a week. Over an average of 2.8 years diabetes developed at 11.0, 7.8 and 4.8 cases per 100 person-years: the lifestyle program cut incidence by 58 percent and the medication by 31 percent. About 7 people would need the program for 3 years to prevent one case. The trial measured diabetes, not A1c itself.13Grade A

  • Structured exercise, more than 150 minutes a week

    lowers it, in people with diabetes

    Across 47 randomized trials and 8,538 people with type 2 diabetes, structured exercise lowered A1c by 0.67 percentage points against control: 0.73 for aerobic training, 0.57 for resistance training and 0.51 for both. Programs over 150 minutes a week lowered it by 0.89 points, programs of 150 minutes or less by 0.36. Advice to be active, without a structured program, changed A1c only when paired with dietary advice. These are people starting from diabetic values; the drop from inside the normal range is smaller and untested.14Grade A

  • Substantial weight loss

    lowers it, in proportion to the weight lost

    In the DiRECT trial, 306 adults diagnosed with type 2 diabetes within the previous six years were randomized by practice to an intensive weight-management program or usual care. At 12 months, 46 percent of the program group and 4 percent of controls were in remission (A1c under 6.5 percent off glucose-lowering drugs). Remission tracked weight: 7 percent of those who lost 0 to 5 kg, 34 percent at 5 to 10 kg, 57 percent at 10 to 15 kg and 86 percent of those who lost 15 kg or more.15Grade B

  • Lower-carbohydrate eating

    lowers it over months; the effect fades by a year

    A meta-analysis of 23 randomized trials and 1,357 people with type 2 diabetes found that low-carbohydrate diets (under 130 g a day) produced remission, defined as an A1c under 6.5, in 57 percent at six months against 31 percent on control diets. Gains in weight, triglycerides and insulin sensitivity were large at six months and had diminished by 12 months, when data were sparse and adherence had slipped.16Grade B

  • Iron deficiency

    raises it without raising glucose

    Among 6,666 US women without diabetes or kidney disease in NHANES, 13.7 percent were iron deficient, and iron deficiency carried 1.39 times the odds of an A1c of 5.5 percent or higher after adjusting for age, ethnicity and waist size. A systematic review of 12 studies found the same direction throughout: iron deficiency, with or without anemia, raised A1c with no rise in glucose, while anemias of other causes may lower it. Correcting the deficiency, not the diet, is what moves this A1c.17,18Grade B

  • Age

    raises it slowly

    In two US cohorts without diabetes, A1c rose by about 0.010 to 0.014 percentage points per year, roughly a tenth of a point per decade, independent of fasting and post-load glucose. Part of the drift from 5.2 at 35 to 5.5 at 65 is physiology, not diet.5Grade C

06 · Reading it well

Caveats, and what belongs with a physician.

Anything that changes how long red cells live changes A1c without changing glucose. Among 12 people, mean red-cell age ranged from 38 to 60 days in those without diabetes, enough to shift A1c by a clinically important amount at the same average glucose. Inherited hemoglobin variants (S, C, E and D, and persistent fetal hemoglobin) can push a result up or down depending on the laboratory's method, so a reading that disagrees with glucose deserves a method check, not a diet.3,19Grade B

The American Diabetes Association lists conditions in which A1c should not be used to diagnose and glucose criteria apply instead: some hemoglobin variants, the second and third trimesters of pregnancy and the postpartum period, G6PD deficiency, HIV, hemodialysis, recent blood loss or transfusion, hemolysis, and erythropoietin therapy. The kidney guideline adds that A1c accuracy and precision decline in advanced chronic kidney disease (stages G4 to G5) and that the measurement has low reliability on dialysis.2,20Grade A

The glucose-to-A1c relationship differs between people. In 104 Black and 104 white people with type 1 diabetes wearing continuous monitors for 12 weeks, A1c ran 0.4 percentage points higher in Black participants at the same mean glucose, while glycated albumin and fructosamine showed no such difference. Too few participants were below 6.5 percent to say whether the gap holds in the normal range.21Grade C

A low A1c is not automatically good news. The excess mortality below 5.0 percent in the cohorts survived exclusion of anemia and adjustment for red-cell indices, and the pooled-cohort investigators suggest that very low glycemia may mark illness such as liver disease rather than cause harm. An unexpectedly low value is a reason to look for a cause, not a target to aim at.7,10Grade B

One A1c is a screen, not a verdict. Within-person variation is about 3.6 percent, and the diagnostic criteria require two abnormal results before a diagnosis is made. Treatment goals in diabetes are set per person, under 7 percent for many adults and a range from under 6.5 to under 8 depending on age, illness and the risk of low blood sugar; they are goals for people already diagnosed and say nothing about the normal range.6,2,22,20Grade A

See a physician

  • An A1c of 6.5 percent or higher on any test, or 5.7 or higher together with thirst, frequent urination, blurred vision or unexplained weight loss.
  • An A1c that disagrees with fasting glucose or a glucose monitor, which may point to anemia, a hemoglobin variant, kidney disease or a red-cell condition that the A1c cannot see.
  • Any A1c during pregnancy or while planning one, where glucose criteria apply and different thresholds are used.
  • An A1c that has risen on consecutive tests, even inside the normal range, especially with a rising waist size, triglycerides or fasting insulin.
  • An unexpectedly low A1c alongside anemia, liver disease, recent blood loss or transfusion, or a medication that affects red cells.

This page is education, not individual medical advice, and reading it creates no physician-patient relationship.

07 · Open questions

What the literature does not settle.

  • No randomized trial has lowered A1c inside the normal range and measured outcomes, so every threshold on this page comes from where risk rose in cohorts, not from a tested goal.
  • Whether the excess mortality below 5.0 percent reflects glucose, hidden illness or red-cell biology is unresolved; the cohorts disagree on whether the lowest-risk point is under 5.0 or at 5.0 to 5.5.
  • The size of an individual's gap between A1c and true average glucose has not been measured in healthy adults; the 0.4-point ethnic difference comes from type 1 diabetes, and glucose-monitor averages are not validated as a substitute for diagnosis.
  • Whether the aging drift in A1c deserves age-specific cutoffs, as the Framingham and NHANES investigators asked, has not been settled.
  • The lifestyle effect sizes come from people with prediabetes or diabetes; how much exercise, weight loss or carbohydrate restriction moves an A1c that is already 5.5 is untested.

08 · In practice

How Dr. Tagge reads it in his own practice.

I like to see hemoglobin A1c under about 5.4 percent, and I read it as a three-month average that can be fooled, never alone. That number is the reference group where risk sat lowest in the long cohorts, and it is my judgment, not a trial target: a 5.5 or 5.6 is a reason to look at fasting insulin, fasting glucose, waist size and the direction of travel, not a label. Below 5.0 I ask why before I congratulate anyone, because the cohorts found more deaths there, and an A1c that disagrees with the glucose usually means the red cells, not the sugar, are telling the story.

A practice judgment, labeled as one (Grade D): it is how one physician reads the number for the people he cares for, not a recommendation for you.

09

Questions

10 · Sources

22 sources, read in full.

Numbered in the order they appear. Each line says what this page relies on from the paper; the link opens the record at PubMed or the publisher.

  1. 1.

    Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ; A1c-Derived Average Glucose Study Group. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008. PMID 18540046. DOI 10.2337/dc08-0545.

    Laboratory method study · In 507 people, average glucose (mg/dL) = 28.7 x A1C minus 46.7, R-squared 0.84, with no difference by age, sex, diabetes type or ethnicity.

  2. 2.

    American Diabetes Association Professional Practice Committee. 2. Diagnosis and Classification of Diabetes: Standards of Care in Diabetes-2025. Diabetes Care. 2025. PMID 39651986. DOI 10.2337/dc25-S002.

    Guideline · A1C 6.5 percent or higher is diabetes and 5.7 to 6.4 prediabetes on an NGSP-certified assay; two abnormal results are required; glucose criteria replace A1C in hemoglobin variants, pregnancy, G6PD deficiency, HIV, hemodialysis, blood loss or transfusion, hemolysis and erythropoietin therapy.

  3. 3.

    Cohen RM, Franco RS, Khera PK, et al.. Red cell life span heterogeneity in hematologically normal people is sufficient to alter HbA1c. Blood. 2008. PMID 18694998. DOI 10.1182/blood-2008-04-154112.

    Laboratory method study · Mean red-cell age ranged from 38 to 60 days in nondiabetic controls, enough to cause clinically important differences in A1c at a given mean glucose.

  4. 4.

    Leong A, Chen J, Wheeler E, et al.. Mendelian Randomization Analysis of Hemoglobin A1c as a Risk Factor for Coronary Artery Disease. Diabetes Care. 2019. PMID 30659074. DOI 10.2337/dc18-1712.

    Mendelian randomization · Genetically higher A1c carried 1.61 times the odds of coronary disease per percentage point; 2.23 through glycemic variants and 1.30 through erythrocytic variants.

  5. 5.

    Pani LN, Korenda L, Meigs JB, et al.. Effect of aging on A1C levels in individuals without diabetes: evidence from the Framingham Offspring Study and the National Health and Nutrition Examination Survey 2001-2004. Diabetes Care. 2008. PMID 18628569. DOI 10.2337/dc08-0577.

    Cross-sectional study · A1c rose 0.010 to 0.014 units per year in adults without diabetes; the 97.5th percentile moved from 5.6 to 6.0 percent under age 40 to 6.2 to 6.6 at 70 and older.

  6. 6.

    Selvin E, Crainiceanu CM, Brancati FL, Coresh J. Short-term variability in measures of glycemia and implications for the classification of diabetes. Archives of Internal Medicine. 2007. PMID 17646610. DOI 10.1001/archinte.167.14.1545.

    Cross-sectional study · Within-person coefficient of variation over two weeks was 3.6 percent for A1c, 5.7 percent for fasting glucose and 16.7 percent for two-hour glucose in 685 adults.

  7. 7.

    Selvin E, Steffes MW, Zhu H, et al.. Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults. New England Journal of Medicine. 2010. PMID 20200384. DOI 10.1056/NEJMoa0908359.

    Prospective cohort · Versus 5.0 to under 5.5 percent, hazards for diabetes were 0.52, 1.86, 4.48 and 16.47 and for coronary disease 0.96, 1.23, 1.78 and 1.95 across A1c categories in 11,092 ARIC adults; all-cause death was J-shaped with excess below 5.0.

  8. 8.

    Zhang X, Gregg EW, Williamson DF, et al.. A1C level and future risk of diabetes: a systematic review. Diabetes Care. 2010. PMID 20587727. DOI 10.2337/dc09-1939.

    Systematic review and meta-analysis · Across 16 studies, five-year diabetes incidence was under 9 percent at A1c 5.0 to 5.5, 9 to 25 percent at 5.5 to 6.0 and 25 to 50 percent at 6.0 to 6.5.

  9. 9.

    Khaw KT, Wareham N, Bingham S, Luben R, Welch A, Day N. Association of hemoglobin A1c with cardiovascular disease and mortality in adults: the European prospective investigation into cancer in Norfolk. Annals of Internal Medicine. 2004. PMID 15381514. DOI 10.7326/0003-4819-141-6-200409210-00006.

    Prospective cohort · In 10,232 adults aged 45 to 79, each percentage point of A1c carried a relative risk of death of 1.24 in men and 1.28 in women; lowest rates below 5 percent; 72 percent of deaths occurred at 5 to 6.9.

  10. 10.

    Emerging Risk Factors Collaboration; Di Angelantonio E, Gao P, Khan H, et al.. Glycated hemoglobin measurement and prediction of cardiovascular disease. JAMA. 2014. PMID 24668104. DOI 10.1001/jama.2014.1873.

    Systematic review and meta-analysis · In 294,998 people from 73 prospective studies, A1c had an approximately J-shaped association with cardiovascular disease and added a C-index change of 0.0018 to conventional risk factors.

  11. 11.

    Cavero-Redondo I, Peleteiro B, Álvarez-Bueno C, Rodriguez-Artalejo F, Martínez-Vizcaíno V. Glycated haemoglobin A1c as a risk factor of cardiovascular outcomes and all-cause mortality in diabetic and non-diabetic populations: a systematic review and meta-analysis. BMJ Open. 2017. PMID 28760792. DOI 10.1136/bmjopen-2017-015949.

    Systematic review and meta-analysis · In people without diabetes, all-cause mortality was higher above 6.0 percent (HR 1.74) and below 5.0 (HR 1.19); lowest-mortality span 5.0 to 6.0 across 46 studies.

  12. 12.

    Selvin E, Ning Y, Steffes MW, et al.. Glycated hemoglobin and the risk of kidney disease and retinopathy in adults with and without diabetes. Diabetes. 2011. PMID 20978092. DOI 10.2337/db10-1198.

    Prospective cohort · In 11,357 ARIC participants over a median 14 years, A1c 5.7 to 6.4 and 6.5 or higher carried kidney-disease hazards of 1.12 and 1.39 and retinopathy odds of 1.42 and 2.91 versus under 5.7, with no detectable threshold.

  13. 13.

    Knowler WC, Barrett-Connor E, Fowler SE, et al.; Diabetes Prevention Program Research Group. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. New England Journal of Medicine. 2002. PMID 11832527. DOI 10.1056/NEJMoa012512.

    Randomized trial · In 3,234 adults with elevated glucose, a lifestyle program cut diabetes incidence by 58 percent and a glucose-lowering medication by 31 percent over 2.8 years.

  14. 14.

    Umpierre D, Ribeiro PA, Kramer CK, et al.. Physical activity advice only or structured exercise training and association with HbA1c levels in type 2 diabetes: a systematic review and meta-analysis. JAMA. 2011. PMID 21540423. DOI 10.1001/jama.2011.576.

    Systematic review and meta-analysis · Across 47 trials and 8,538 people with type 2 diabetes, structured exercise lowered A1c by 0.67 points; 0.89 above 150 minutes a week versus 0.36 at or below.

  15. 15.

    Lean ME, Leslie WS, Barnes AC, et al.. Primary care-led weight management for remission of type 2 diabetes (DiRECT): an open-label, cluster-randomised trial. Lancet. 2018. PMID 29221645. DOI 10.1016/S0140-6736(17)33102-1.

    Randomized trial · At 12 months, 46 percent of the weight-management group versus 4 percent of controls reached remission (A1c under 6.5 off drugs); 86 percent of those losing 15 kg or more.

  16. 16.

    Goldenberg JZ, Day A, Brinkworth GD, et al.. Efficacy and safety of low and very low carbohydrate diets for type 2 diabetes remission: systematic review and meta-analysis of published and unpublished randomized trial data. BMJ. 2021. PMID 33441384. DOI 10.1136/bmj.m4743.

    Systematic review and meta-analysis · Across 23 trials and 1,357 people with type 2 diabetes, low-carbohydrate diets produced remission (A1c under 6.5) in 57 percent versus 31 percent at six months, with gains diminishing by 12 months.

  17. 17.

    Kim C, Bullard KM, Herman WH, Beckles GL. Association between iron deficiency and A1C Levels among adults without diabetes in the National Health and Nutrition Examination Survey, 1999-2006. Diabetes Care. 2010. PMID 20067959. DOI 10.2337/dc09-0836.

    Cross-sectional study · Among 6,666 women without diabetes, 13.7 percent were iron deficient, and iron deficiency carried 1.39 times the odds of an A1c of 5.5 percent or higher.

  18. 18.

    English E, Idris I, Smith G, Dhatariya K, Kilpatrick ES, John WG. The effect of anaemia and abnormalities of erythrocyte indices on HbA1c analysis: a systematic review. Diabetologia. 2015. PMID 25994072. DOI 10.1007/s00125-015-3599-3.

    Review · Across 12 studies, iron deficiency with or without anemia raised A1c without raising glucose; non-iron-deficiency anemia may lower it.

  19. 19.

    Little RR, Roberts WL. A review of variant hemoglobins interfering with hemoglobin A1c measurement. Journal of Diabetes Science and Technology. 2009. PMID 20144281. DOI 10.1177/193229680900300307.

    Review · Hemoglobin variants S, E, C and D and elevated fetal hemoglobin interfere with some A1c methods, raising or lowering the result depending on the assay.

  20. 20.

    Kidney Disease: Improving Global Outcomes (KDIGO) Diabetes Work Group. KDIGO 2022 Clinical Practice Guideline for Diabetes Management in Chronic Kidney Disease. Kidney International. 2022. PMID 36272764. DOI 10.1016/j.kint.2022.06.008.

    Guideline · A1c accuracy and precision decline in CKD stages G4 to G5 and the test has low reliability on dialysis; individualized targets run from under 6.5 to under 8.0 percent in CKD not on dialysis.

  21. 21.

    Bergenstal RM, Gal RL, Connor CG, et al.; T1D Exchange Racial Differences Study Group. Racial Differences in the Relationship of Glucose Concentrations and Hemoglobin A1c Levels. Annals of Internal Medicine. 2017. PMID 28605777. DOI 10.7326/M16-2596.

    Prospective cohort · In 104 Black and 104 white people with type 1 diabetes, A1c was 0.4 percentage points higher in Black participants at the same continuous-monitor mean glucose; too few below 6.5 percent to generalize.

  22. 22.

    American Diabetes Association Professional Practice Committee. 6. Glycemic Goals and Hypoglycemia: Standards of Care in Diabetes-2025. Diabetes Care. 2025. PMID 39651981. DOI 10.2337/dc25-S006.

    Guideline · An A1C goal under 7 percent is appropriate for many nonpregnant adults without significant hypoglycemia; less stringent goals where harms outweigh benefits.

Related

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Reading a number well is the start of the work, not the end of it. If you would like a physician to read yours over time, Explore working with Dr. Tagge.