Estimated Average Glucose (eAG) Calculator

Algorithm

As a tool that evaluates blood glucose levels, this calculator accounts for the HbA1c testing and transforms the percentage provided by it in a target number that can easily be followed. This target number represents the desired glucose level in either mg/dL or mmol/L.

The formula used by the estimated average glucose eAG calculator is based on a linear regression equation model and is the following:

eAG = (28.7 x hemoglobin A1c) - 46.7

The transformation is not said to be impacted significantly by gender, age, type of diabetes or race, therefore there are no limitations of usage.

eAG and HbA1c

The eAG is used as a target value that is set by the clinician as glycemic control and is often used in cases where the patient is not compliant to therapy, doesn’t check blood glucose often enough or keep track of self-monitoring.

HbA1c is an index of average glucose that can reveal evolution of blood glucose for weeks up to months. The method however is weighted, therefore, the preceding month weights more than the other three.

The term eAG was introduced by the American Diabetes Association (ADA), to facilitate translation of the A1c result to a value that is closer to the readings on glucose meters that patients are used to.

Glycosylated hemoglobin, HbA1c can change significantly with AG, as being showed by regular testing.

The following table introduces the translation of HbA1c in % to eAG in mg/dL and mmol/L:

HbA1c is considered to be the best overall glucose control test because it measures the glucose molecules attached to haemoglobin. The patient only has to compare the target eAG value set by the clinician after the A1c test with the blood glucose reading from the meter.

ADA recommends from 2 to 4 A1c tests per year. The results considered desirable is under 6% (meaning 6% of haemoglobin has glucose bound to it), which translated into an eAG of 126 mg/dL or 7 mmol/L.

Blood glucose conversion

Blood sugar levels can be measured in either mg/dL or mmol/L. These are the conversion rules between the two:

■ mg/dL x 0.0555 = mmol/L

■ mmol/L x 18,0182 = mg/dL

The table consists of the most common values:

About the original study

The original study was aimed at providing a mathematical relationship between A1c and average glucose levels.

The study consisted of 507 subjects (268 with type 1 diabetes, 159 with type 2 diabetes and 80 non-diabetic). AG levels were monitored constantly and at the end of a three-month period, A1c tests were performed.

Linear regression was used between the A1c and AG values obtained from the subjects and the tightest correlation was: AG(mg/dl) = 28.7 x A1C - 46.7, R(2) = 0.84, P < 0.0001 .

The study also emphasized that no significant differences were found because of patient variables such as age, gender, type of diabetes, ethnicity or smoking status.

David M. Nathan MD is director of the General Clinical Research Center and of Diabetes Center at Massachusetts General Hospital. Most of research focuses on therapies for type 1 and 2 diabetes and complication prevention. Browse Dr. Nathan’s publications on PubMed.

Original source

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; 31(8):1473-8.

Other references

1. Koenig RJ, Peterson CM, Jones RL, Saudek C, Lehrman M, Cerami A. Correlation of glucose regulation and hemoglobin AIc in diabetes mellitus. N Engl J Med. 1976; 295(8):417-20.

2. Kim HY, Lee SY, Suh S, Kim JH, Lee MK, Park HD. The relationship between estimated average glucose and fasting plasma glucose. Clin Chem Lab Med. 2013; 51(11):2195-200.