A1C Calculator

HbA1c explained

As a clinical determination, the glycated haemoglobin test offers a quick way of checking whether the patient respects the self care plan and keeps their blood sugar levels in the desired range.

There are two important concepts that are in use:

■ Average blood sugar – measured in mg/dL;

■ A1C level – index value.

Normal glucose tests provide a value in mg/dL which has a percentage equivalent, the A1C.

■ To estimate the A1C level, the conversion from average blood sugar needs to take place:

Step 1: Calculate A = Average Blood Sugar + 46.7

Step 2: Calculate A1C level = A/28.7

■ To estimate the average Blood Sugar level from A1C:

Step 1: Calculate A = A1C level x 28.7

Step 2: Calculate Average Blood Sugar = A – 46.7

A1C interpretation

The A1C value is obtained after a specialized test (to be performed twice a year) and provides a good indicator of the level of blood sugar control.

The A1C cells from the blood stream naturally attach glucose, therefore the higher the sugar level in the blood, the higher the percentage of glycated cells.

Since the A1C cells have a life span of up to 4 months, the physical test can reveal long term diabetes activity and efficiency of blood sugar control.

The target for normal A1C is below 5.7%. Values between 5.7 and 6.4 indicate pre-diabetes whilst all values above 6.5% are suggestive of diabetes.

About the study

The A1C essay expresses the percent of haemoglobin which is ghycated. This offers information on chronic glycemia.

The study conducted by Nathan et al. in 2008 was aimed at finding the mathematical relationship between A1C and average glucose (AG) levels. This was thought to facilitate self monitoring.

The study cohort included a total of 507 subjects (268 patients with type 1 diabetes, 159 with type 2 diabetes, and 80 nondiabetic).

Their A1C levels were obtained after 3 months and compared to their AG levels during the same period. Average glucose values were obtained by combining weighted results from at least 2 days of continuous glucose monitoring. This was performed via seven-point daily self-monitoring of capillary (fingerstick) glucose for at least 3 days a week.

Linear regression analysis between the A1C and AG values provided the tightest correlations where AG(mg/dl) = 28.7 x A1C - 46.7.

It was also found that the linear regression equations did not show any significant differences across gender, age, ethnicity or diabetes type, therefore the conversion can be used for almost all patients with type 1 and 2 diabetes.

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. Diabetes UK. (2009) HbA1c Standardisation For Laboratory Professionals

2. Choi, SH et al. Hemoglobin A1c as a Diagnostic Tool for Diabetes Screening and New-Onset Diabetes Prediction. A 6-year community-based prospective study. Diabetes Care. 2011; 34(4): 944–949.