The normal reference range for the glycosylated hemoglobin A1c is 4.0% to 6.0%. This test measures the amount of glucose that has become permanently bound to the red blood cells from circulating glucose. Erythrocytes live for about 120 days, giving feedback about blood glucose for past 120 days. Elevations in the blood glucose level will cause elevations in the amount of glycosylation. Thus the test is useful in identifying clients who have periods of hyperglycemia that are undetected in other ways. The estimated average glucose for a glycosylated hemoglobin A1c of 9% is 212 mg/dL (11.8 mmol/L). Elevations indicate continued need for teaching related to the prevention of hyperglycemic episodes.