HbA1c
HbA1c measures the fraction of hemoglobin that sugar molecules have permanently attached to. Because red blood cells live about three months, the number reflects average blood glucose over that entire window rather than any single day. Laboratories label anything below 5.7 percent normal and 6.5 percent or higher diabetes. Yet the lowest cardiovascular and mortality risk sits near 5.0 to 5.4 percent, well inside the supposedly normal range. Each percentage point drop in HbA1c reduces diabetic eye, kidney, and nerve damage more reliably than it lowers heart attack risk, a gap that reshaped how the marker is used. Conditions that shorten or lengthen red blood cell lifespan, such as anemia, can distort the result in either direction. As a single blood draw summarizing months of metabolic control, HbA1c remains one of the most practical windows into long-term diabetes and cardiovascular risk.
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