Assessing metabolic health: where HbA1c falls short, and how it compares to fasting glucose, CGM, and OGTT

The onset of type II diabetes (T2D) is slow and often asymptomatic until it has reached an advanced stage, by which point years of damage have likely already been done. Rather than wait for the onset of symptoms, T2D can be detected at earlier stages using metrics related to the disease’s most damaging characteristic, the impairment of glycemic control. Specifically, current clinical diagnostics rely on measurements of fasting plasma glucose, plasma glucose levels in response to an oral glucose tolerance test (OGTT), and, most recently, hemoglobin A1c, or HbA1c (and by “most recently” I mean over the past fifteen years). But while these tests are the most commonly used, are they all equally sufficient for detecting early stages of metabolic disease? Where does each succeed, and where does each fall short?