1. HbA1cDefinitionHbA1c is a test that measures the amount of glycated hemoglobin in your blood.Glycated hemoglobin is a substance in red blood cells that is formed when blood sugar(glucose) attaches to hemoglobin.Alternative NamesGlycated hemoglobin; Glycosylated hemoglobin; Hemoglobin - glycosylated; A1C;GHb; Glycohemoglobin; Diabetic control indexHow the Test is PerformedBlood is drawn from a vein, usually from the inside of the elbow or the back of the hand.The puncture site is cleaned with germ-killing medicine (antiseptic). The health careprovider wraps an elastic band around the upper arm to apply pressure to the area andmake the vein swell with blood.Next, the health care provider gently inserts a needle into the vein. The blood collectsinto an airtight vial or tube attached to the needle. The elastic band is removed from yourarm. Once the blood has been collected, the needle is removed, and the puncture site iscovered to stop any bleeding.In infants or young children, a sharp tool called a lancet may be used to puncture the skinand make it bleed. The blood collects into a small glass tube called a pipette, or onto aslide or test strip. A bandage may be placed over the area if there is any bleeding.How to Prepare for the TestNo special preparation is necessary.How the Test Will FeelWhen the needle is inserted to draw blood, you may feel moderate pain, or only a prick orstinging sensation. Afterward, there may be some throbbing.Why the Test is PerformedYour doctor may order this test if you have diabetes. It is used to measure your bloodsugar control over several months. It can give a good estimate of how well you havemanaged your diabetes over the last 2 or 3 months.
2. You have more glycated hemoglobin if you have had high levels of glucose in yourblood. In general, the higher your HbA1c, the higher the risk that you will developproblems such as: • Eye disease • Heart disease • Kidney disease • Nerve damage • StrokeThis is especially true if your HbA1c remains high for a long period of time.The closer your HbA1c is to normal, the less risk you have for these complications.Normal ResultsAn HbA1c of 6% or less is normal. If you have diabetes, you should try to keep yourHbA1c level at or below 7%. However, you and your health care provider must decidewhat is a normal HbA1c level for you.Normal ranges may vary slightly among different laboratories. Talk to your doctor aboutthe meaning of your specific test results.What Abnormal Results MeanAbnormal results mean that your blood glucose levels have been above normal over aperiod of weeks to months. If your HbA1c is above 7%, it means that your diabetescontrol may not be as good as it should be.High values mean you are at greater risk of diabetes complications. If you can bring yourlevel down, you decrease your chances of long-term complications.Ask your doctor how often you should have your HbA1c tested. Usually, doctorsrecommend testing every 3 or 6 months.RisksVeins and arteries vary in size from one patient to another and from one side of the bodyto the other. Obtaining a blood sample from some people may be more difficult than fromothers.Other risks associated with having blood drawn are slight but may include: • Excessive bleeding • Fainting or feeling light-headed • Hematoma (blood accumulating under the skin)
3. • Infection (a slight risk any time the skin is broken)ReferencesAmerican Diabetes Association. Standards of medical care in diabetes -- 2009. DiabetesCare. 2009;32:S13-S61.Inzucchi SE, Sherwin RS. Type 1 diabetes mellitus. In: Goldman L, Ausiello D, eds.Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 247.Inzucchi SE, Sherwin RS. Type 2 diabetes mellitus. In: Goldman L, Ausiello D, eds.Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 248.
4. What is the HbA1C? • HbA1c • Two examples: poor control & good control • When should the HbA1c be measured • Illustrated diagramatically • Comparision of glucose and HbA1c levels • Large animation • HbA1c to blood glucose convertor (link) • Helpful linkThe HbA1cEnlarge Haemoglobin, in your blood, joins up with glucose to form the chemical called HbA1cIn the blood stream are the red blood cells, which are made of a molecule, haemoglobin.Glucose sticks to the haemoglobin to make a glycosylated haemoglobin molecule, calledhaemoglobin A1C or HbA1C. The more glucose in the blood, the more haemoglobinA1C or HbA1C will be present in the blood.Red cells live for 8 -12 weeks before they are replaced. By measuring the HbA1C it cantell you how high your blood glucose has been on average over the last 8-12 weeks. Anormal non-diabetic HbA1C is 3.5-5.5%. In diabetes about 6.5% is good.The HbA1C test is currently one of the best ways to check diabetes is under control; it isthe blood test that gets sent to the laboratory, and it is done on the spot in some hospitalclinics. Remember, the HbA1C is not the same as the glucose level.Coincidentally the glucose/HbA1C numbers for good control are rather similar though inthe UK and Europe: glucose levels averaging 6.5 mmols/l before meals is equivalent to7% HbA1C (glucose levels are higher after meals) (see below).
5. Two examplesBelow are two examples of people who have their HbA1c measured. One is poorlycontrolled, one well controlled.A graph of glucose changes over 9 Here the glucose changes between 5-9. weeks. The glucose (green This results in an HbA1c level line) changes between 7-12. of 7% at the end of the 9 weeks. This results in an HbA1c level Well controlled. of 10% at the end of the 9 weeks (red line). Poorly controlled.When should the HbA1C be measured?Measure HbA1c • every 3 months if trying to improve • evey 6 months if very stable •If your diabetes is controlled (basically an HbA1C lower than 7%), every 3-6 months.
6. But if the last reading is above 7% and you are in reasonable health, you will need toachieve a lower level if possible, and the next reading should be sooner. This assumesyou will make changes to improve your control. There is no point in having your HbA1cmeasured if you are not trying to achieve good control of your diabetes, although thelevel does predict the likelihood of complications from your diabetes.Your ideal HbA1c depends on your general health, and whether or not you use insulin,etc, and is discussed here.Illustrated diagrammatically Haemoglobin in the blood (red, rectangle) combines with glucose in the blood (green, circle) to form glycosylated haemoglobin. This reaction occurs over a 10 week period.Controlled diabetes, not much glucose, not much glycosylated Uncontrolled diabetes, more glucose, haemoglobin much more glycosylated
7. haemoglobinGlucose levels fluctuate from minute to minute, hour to hour, and day to day. Thus forhour to hour control, or day to day, a glucose level is the best guide.The HbA1C level changes slowly, over 10 weeks, so it can be used as a quality controltest.In diabetes glucoses tend to rise more than usual, dropping with exercise, rising afterfood, rising a lot more after sweet food, and can make it hard to control.For how to lower the HbA1C to achieve better control (and better health in the longterm), see the pages type 1 diabetes/insulin (type2) or type 2 diabetes (no insulin). Goodcontrol produces benefits that lasts 10 years at least (NEJM 2008).How does your glucose level compare with your HbA1c HbA1c % Average blood glucose level mmol/l13 1812 1711 1510 139 128 107 86 75 5HbA1c levels by coincidence nearly equate to glucose levels. So an HbA1c level of 10%means the average glucose level for the previous 10 weeks was 13mmol/l.
8. But at lower levels there is even less difference, so an HbA1c of 7% means the averageglucose level was 8mmols/l.