Glycosylated Hemoglobin Testing
Hemoglobin A1c (HbA1c)
The glycosylated hemoglobin test (HbA1c) is a simple lab test that shows the average amount of sugar that
has been in your blood over the last three months. This test is used to give you and your doctor the most
accurate picture of your overall diabetes control. Here’s how it works.
Red blood cells are produced in the bone marrow and circulated in the blood stream for approximately 120
days.1 During this time the red blood cells (RBC) are responsible for carrying oxygen to the tissues and
organs of your body. The specific cell part that carries the oxygen is called hemoglobin. During circulation,
glucose that is not used for energy is left in the blood where it attaches itself to the hemoglobin through a
process called glycosylation. Once glycated, a hemoglobin molecule stays that way throughout the lifecycle
of its RBC. The percent of glycosylation is proportional to time and concentration of glucose. In other
words, older RBC’s will have a greater percent of glycosylated hemoglobin (GHb). Also, poorly controlled
diabetics (those who have experienced periods of high concentrations of blood glucose) will have a greater
percent of GHb. Elevated levels of GHb are strongly associated with complications of diabetes.
Research has proven that good control of diabetes is the best way to prevent or delay complication of the
disease that include heart disease, blindness, nerve damage, and kidney damage. While daily blood glucose
monitoring tells you how your blood sugar is doing right then (allowing you to make necessary changes in
medicine, food, and exercise), the HbA1c test gives you a picture of your long term diabetes management
success. The HbA1c test measures the proportion of the hemoglobin molecule in your red blood cells that
has glucose attached to them (thus are “glycated”).2 Glycosylated hemoglobin can be separated by
electrophoresis into three fractions called HbA1a, HbA1b, and HbA1c. Normally only HbA1c is
quantitated.
Diabetes mellitus patients should have an HbA1c test every three to six months, depending on their
treatment program and level of control. HbA1c levels under 6% are normal for people without the disease.3
The American Diabetes Association recommends that HbA1c levels be below 7% for diabetics.2 Studies
have shown that diabetics that can maintain levels in the 7% range have a much better chance of delaying
complications than those in the 9% range.2 ( In August 2001, The American College of Endocrinology and
The American Association of Clinical Endocrinologist released clinical practice guidelines proposing that
the target HbA1c be dropped to 6.5% or lower.)4
Since the HbA1c test indicates the average blood sugar level, and is not affected by short term changes, it
isn’t necessary for patients to be fasting before collection of the blood sample. A properly collected purple
top tube is the required specimen for testing. Allow 48 hour turn-around time for result reporting. HHLA’s
trended report (3 previous results) should prove helpful in the monitoring of long term diabetes
management.
1)”What is HbA1c?” Diabetes Technologies ,Inc. pg.1-2,http://wwwhealthtology.com/dti/WhatisA1c.htm copyright 1998
2) “HbA1c-The 7-Percent Solution” Diabetic Gourmet Magazine,pg1-2,http://diabeticgoutmet.com/articles/155.shtml
copyright 2000
3) “Glycosylated Hemoglobin Testing”, Diabetes & Hormone Center of the Pacfic,pg1-2,http:www.endocrinologist.
com/Hemoglobin.htm, copyright 1996
4) “World Leaders In Endocrinology Call For New Diabetes Guidelines” American Association of Clinical
Endocrinologists, pg 1-4, http://www.aace.com/pub/press/releases/index.php?r=20010821,copyright2002