Comparison of Blood Glucose, HbA1c, and Fructosamine

The hemoglobin A1c is an important part of long term blood glucose monitoring. Here’s how you can get more from your test results.

Remember, the hemoglobin A1c result must be compared to the normal range for each particular lab. Eventually that normal range will be standardized to a range of 4-6% but some labs still have ranges that are quite different.

To convert the A1c to average blood glucose, consider the high end of the normal range (e.g. if normal is 4-6%, then 6%) is equal to 120 mg/dl. For each change in 1% of A1c, there is a corresponding increase or decrease of approximately 30 mg/dl average plasma glucose. (Please see chart below for examples.)

HbA1c is one of 3 hemoglobin molecules that makes up red blood cells. Glucose attaches slowly to this molecule of hemoglobin over 120 days. Glucose will attach to hemoglobin based on the amount of glucose available. Thus, a glycosolated hemoglobin lab value provides average blood glucose levels during a 1-4 month period.

Fructosamine (glycated albumin) measures short term control of blood sugar for the past 1-3 weeks. Each 75 µmol change equals a change of approximately 60 mg/dl blood sugar or 2% HbA1c.

Approximate Comparison of Blood Glucose,  HbA1c , & Fructosamine Levels
Glucose (mg/dl)	Fructosamine (µmol)	HbA1c (%)
90	212.5	5.0
120	250	6.0
150	287.5	7.0
180	325	8.0
210	362.5	9.0
240	400	10.0
270	437.5	11.0
300	475	12.0
330	512.5	13.0
360	550	14.0
390	587.5	15.0

Normal HbA_1c Range 4-6%

 

Nathan, D.M. et. al. The clinical information value of the glycosylated hemoglobin assay. NEJM, 1984; 310:341-346.