What test measures the average glucose level over the past 120 days?

The Hemoglobin A1C test is specifically designed to measure the average blood glucose levels over the past two to three months, typically around 120 days. This test works by assessing the percentage of hemoglobin that is coated with glucose, which reflects the average glucose concentration in the blood.

When glucose is present in the bloodstream, it binds to hemoglobin, the protein in red blood cells that carries oxygen. Since red blood cells have a lifespan of approximately 120 days, the A1C measurement provides insight into glucose levels over this time frame.

This makes the Hemoglobin A1C test a valuable tool for diagnosing and monitoring diabetes, as it helps healthcare providers understand a patient's long-term glucose control rather than just their blood sugar at a single point in time. In contrast, other tests such as fasting plasma glucose and the oral glucose tolerance test measure blood sugar at specific moments rather than providing a cumulative average over an extended period. Continuous glucose monitoring provides real-time blood glucose readings but does not summarize historical averages in the same way.