What blood test measures the amount of glucose that attaches to hemoglobin on red blood cells?

The test that measures the amount of glucose that attaches to hemoglobin on red blood cells is the HbA1C test, which is also known as the glycated hemoglobin test. This test provides an average blood glucose level over the past two to three months, making it an important tool for managing diabetes.

When glucose levels are high, more glucose molecules can bind to hemoglobin, the protein in red blood cells that carries oxygen. By measuring the percentage of hemoglobin that is glycated (attached to glucose), healthcare providers can assess a patient's long-term glucose control. This metric is particularly useful because it reflects the overall trends in blood sugar levels rather than fluctuations that might occur on a day-to-day basis.

The other tests listed have different purposes. Fasting blood sugar tests measure glucose levels at a single point in time after fasting, while insulin level tests measure the concentration of insulin in the blood, but neither provides the long-term average like the HbA1C test does. Glycohemoglobin test is actually another name for the HbA1C test, indicating its function as a marker of blood glucose control over time. Therefore, the correct answer aligns with the fundamental purpose of determining glucose attachment to hemoglobin.