A nurse is reinforcing teaching with an adolescent client about the purpose of the glycosylated hemoglobin (HbA1c) test. Which of the following descriptions should the nurse include in the teaching?

A. "It measures the amount of oxygen circulating in the blood." The HbA1c test does not measure oxygen levels. Oxygen levels in the blood are measured through tests like pulse oximetry or arterial blood gas tests. B. "It measures the amount of immature white blood cells." The HbA1c test measures the average blood glucose levels over the past 2-3 months, not white blood cells. The immature white blood cell count is assessed through a different blood test (e.g., a complete blood count). C. "It measures the glucose circulating in the blood stream." The HbA1c test reflects the average blood glucose levels over the past 2-3 months by measuring the percentage of hemoglobin that has glucose attached to it. D. "It measures the amount of red blood cells." The HbA1c test does not measure the number of red blood cells; it measures the percentage of hemoglobin in red blood cells that is bound to glucose, which helps assess blood sugar control over time.