The HbA1c blood test — also called glycosylated hemoglobin, glycohemoglobin or A1c — estimates how well blood sugar has been controlled during the previous three to four months.
Over time, glucose attaches to tissues in the body. The HbA1c test measures the percentage of hemoglobin molecules in the red blood cells that have glucose attached. Since red blood cells last an average of four months before the body makes new blood cells, this test can indicate the average blood glucose levels over the life span of the blood cells being tested.
To perform the test, blood usually is drawn from a vein and sent to a laboratory. The Pediatric Diabetes Clinic at UCSF Children's Hospital uses a device, called a DCA 2000 Analyzer, that reads small blood samples drawn from the fingertip, just like a blood glucose monitoring test. The blood drop is applied to a cartridge and read by the device in the clinic. The HbA1c test result is available in just six minutes.
The HbA1c test is a way to assess blood glucose control over time. It represents an "average" blood glucose level. However, it does not replace the need for home blood glucose monitoring on a daily basis. The individual readings from the home blood glucose monitors show specific times of day when the blood glucose levels may rise or fall outside of target ranges. Daily blood glucose records can be reviewed to fine tune therapy decisions, such as adjusting insulin doses.
Normal ranges vary slightly depending on the laboratory being used. HbA1c is expressed as a percentage and in general the non-diabetic range is 4 percent to 6 percent.
The American Diabetes Association has set age appropriate targets for HbA1c, which include:
The chart below shows the HbA1c test result as a percentage and the corresponding average blood glucose level.
| HbA1c | Average Blood Glucose (g) |
| 4 | 65 |
| 5 | 100 |
| 6 | 135 |
| 7 | 170 |
| 8 | 205 |
| 9 | 240 |
| 10 | 275 |
| 11 | 310 |
| 12 | 345 |
| 13 | 380 |
| 14 | 415 |
Elevated HbA1c levels increase the risk of long-term complications associated with poorly controlled diabetes. Possible complications include eye, kidney, nerve and heart disease and other health problems. These problems develop slowly over time and the long-term risk is related to the average of the HbA1Cs over time. Each 1 percent reduction in the HbA1c test result reduces the risk of complications by up to 30 percent. Levels less than 7 percent reduce the risk dramatically.
If the HbA1c falls below the target range, there may be increased frequency or severity of low blood sugar reactions.
Generally, the HbA1c test is performed every three months. It may be appropriate for some patients to have the test done less frequently. Your doctor or nurse can provide guidelines for you.
Review Date: 4/26/2007
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