Estimated Average Glucose (eAG) From HbA1C

id

1299

full_title

Estimated Average Glucose (eAG) From HbA1C

short_title

Est. Avg. Glucose from HbA1C

med_description

Estimates an average glucose level from Hemoglobin A1C value.

description

The Estimated Average Glucose (eAG) From HbA1C calculator estimates an average glucose level from Hemoglobin A1C value.

keywords

Estimated Average Glucose (eAG) From HgbA1C, eAG, AG, HgbA1C, hgba1c, hgb a1c eAc, glucose in dm, glucose in DM hgb, hgb DM, diabetes hgb, diabetes h1c calc, diabetes h1c score, diabetes avg glucose, dm average glucose, dm avg glucose

complaint

[ "Dizziness", "Polyuria", "Weakness" ]

formula

eAG = (28.7 ×A1CUS units) - 46.7

evidence

This tool derives from a 2009 paper by Nathan et al., whose purpose was to correlate A1c with 3-month continuous glucose monitor (CGM)/self-monitored glucose readings. In this multicenter, international observational study, 507 patients were analyzed (268 with DM type 1 and 159 with DM type 2). All patients included in the study were non-pregnant adults (ages 18-70) with the following characteristics:

• Non-diabetes patients with no history of diabetes, plasma glucose <97 mg/dL after overnight fast and A1c <6.5%.

• Diabetes patients with stable glycemic control (two A1c values within 1% of each other in the 6 months before recruitment).

Patients excluded from the study were the following:

• Children <18 years.

• Conditions that could result in major glycemic change (diseases that could require steroids, or plans for pregnancy).

• Conditions or treatments that interfere with A1c measurement or A1c-AG relationship: hemoglobinopathies, anemia, altered erythrocyte turnover.

• Inadequate continuous glucose monitoring data.

• Technical issues with A1c samples including sample degradation due to storage or shipment problems.

The linear regression line for comparison to CGM or to seven-point fingerstick separately was not statistically significant for slope and intercept. No significant difference for slope or intercept was seen in any subgroup comparison (sex, diabetes type, age, ethnicity, smoking status), but there was a suggestion (p=0.07) that the regression line was different for Black individuals such that a given value of A1c might have a slightly lower mean glucose level in this population. R2 = 0.84, p<0.0001. Correlation between A1c and reported blood glucose was found with 90% of the estimates within the +/- 15% range of the regression line.

Robust data collection throughout the day and night was achieved by utilizing frequent seven-point glucose measurements, establishing a mathematical relationship that could be easily applied in clinical settings to improve patient understanding of glycemic control. 

Areas for future research include additional study in populations of Asian and African descent (as these were underrepresented), along with controlling for individual variation in red blood cell lifespan and glucose uptake. 

A recently published retrospective observational study compared CGM-derived estimated average glucose with the Nathan et al. equation and found that the combination of data improved the accuracy of average glucose estimation, by reducing the mean absolute error to 1-15 mg/dL.

measurements

[ { "name": "Hemoglobin A1C", "unit": "hgba1c", "error_min": "1", "error_max": "30", "warn_min": "3", "warn_max": "12", "conversion": "1", "normal_max_si": "5.6", "normal_max_us": "5.6", "normal_min_si": "4", "normal_min_us": "4", "units_si": "% gly Hgb", "units_us": "% gly Hgb" } ]

information

refrences

{ "Clinical Practice Guidelines": [ { "href": "https://pubmed.ncbi.nlm.nih.gov/38078586/", "text": "American Diabetes Association Professional Practice Committee. 6. Glycemic goals and hypoglycemia: standards of care in diabetes-2024. Diabetes Care. 2024;47(Suppl 1):S111-S125." } ], "Manufacturer Website": [], "Original/Primary Reference": [ { "href": "https://www.ncbi.nlm.nih.gov/pubmed/18540046", "text": "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 Aug;31(8):1473-8. Epub 2008 Jun 7. Erratum in: Diabetes Care. 2009 Jan;32(1):207. PubMed PMID: 18540046; PubMed Central PMCID: PMC2742903." } ], "Other References": [], "Outcomes": [], "Validation": [ { "href": "https://pubmed.ncbi.nlm.nih.gov/38394636/", "text": "Veronica Tozzo, Matthew Genco, Shammah O. Omololu, Christopher Mow, Hasmukh R. Patel, Chhaya H. Patel, Samantha N. Ho, Evie Lam, Batoul Abdulsater, Nikita Patel, Robert M. Cohen, David M. Nathan, Camille E. Powe, Deborah J. Wexler, John M. Higgins; Estimating Glycemia From HbA1c and CGM: Analysis of Accuracy and Sources of Discrepancy. Diabetes Care 23 February 2024; 47 (3): 460–466" } ], "Validations": [] }

pearls

• HbA1c is inaccurate in the setting of hemoglobinopathies or altered red blood cell turnover.

• HbA1c will be falsely high in untreated anemia, hemoglobin variants, uremia, pregnancy (3rd trimester).

• HbA1c will be falsely low in acute blood loss, hemolysis, chronic liver disease, dialysis, transfusions, cystic fibrosis, pregnancy (2nd trimester).

• HbA1c reflects a 3-month glucose average, so it does not provide a metric of glucose variability (e.g., hypoglycemia or hyperglycemia episodes) or recent glycemic changes, such as acute illness.
• However, the 3-month average does factor in postprandial and nocturnal values which may not be captured by intermittent self-monitoring with a glucometer.

usecase

For translating HbA1c results into 3-month average glucose equivalents.

reasons

Enhances patient-clinician communication by framing the HbA1c in terms that are familiar for patients and comparable to available methods of self-monitoring by glucometer or continuous glucose monitor (CGM).

next_advice

• Knowing an estimated average glucose can allow clinicians to share a target for self-monitored glucose levels in terms that are familiar to patients.
• Always compare HbA1c and available self-monitoring glucose data. While there is some room for individual variation in red blood cell lifespan and glucose uptake, significant discrepancies may require investigation of red blood cell turnover issues.
• If HbA1c is considered unreliable due to an underlying medical condition, alternative tools for longitudinal glucose surveillance include the glucose management indicator (GMI) on a continuous glucose monitor (CGM), fructosamine, glycated albumin, and 1,5-anhydroglucoitol tests. Consult an endocrinologist for further guidance.

next_actions

next_management

diseases

[ "Diabetes Mellitus" ]

instructions

Enter HbA1c value in percent (%) for output of estimated average glucose in mg/dL (mmol/L).

published

2022-04-21T20:28:57.965Z

purpose

[ "Formula" ]

search_terms

[ "dm", "diabetes mellitus", "hyperglycemia", "hypoglycemia", "average glucose", "a1c" ]

seo

{ "keywords_en": "Estimated Average Glucose (eAG) From HgbA1C, eAG, AG, HgbA1C, hgba1c, hgb a1c eAc, glucose in dm, glucose in DM hgb, hgb DM, diabetes hgb, diabetes h1c calc, diabetes h1c score, diabetes avg glucose, dm average glucose, dm avg glucose", "meta_description_en": "The Estimated Average Glucose (eAG) From HbA1C calculator estimates an average glucose level from Hemoglobin A1C value." }

specialty

[ "Emergency Medicine", "Endocrinology", "Family Practice", "Geriatrics", "Hospitalist Medicine", "Internal Medicine", "Pediatrics" ]

departments

[ "Endocrine and Metabolic" ]

tags

[]

version_number

1

versions

[]

related

[ { "calcId": 10529, "short_title_en": "C-Peptide to Glucose Ratio", "slug": "c-peptide-glucose-ratio" }, { "calcId": 50, "short_title_en": "Sodium Correction for Hyperglycemia", "slug": "sodium-correction-hyperglycemia" }, { "calcId": 10522, "short_title_en": "IDF-DAR Fasting Risk Assessment", "slug": "international-diabetes-federation-diabetes-ramadan-alliance-idf-dar-fasting-risk-assessment" } ]

ismed

false

section

[ "whenToUseViewed", "pearlsPitfallsViewed", "whyUseViewed", "nextStepsViewed", "evidenceViewed" ]

cleaned_departments

[ "endocrine" ]

cleaned_use

[ "For translating HbA1c results into 3-month average glucose equivalents." ]

pub

true