Diabetes, HbA1c, and hidden measurement bias

HbA1c is useful because it reflects glycation over the lifespan of red blood cells. That strength becomes a limitation when red cells do not survive for the usual duration.

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Can G6PD deficiency make HbA1c underestimate diabetes? explains the cohort evidence, why the effect differs biologically, and why personal diagnostic decisions still require a clinician and corroborating measurements.

Why this is an equity question

G6PD deficiency is common in populations with African, Mediterranean, Middle Eastern, and Asian ancestry. A biomarker that behaves differently across biological contexts can create unequal diagnosis or treatment even when the same threshold is applied to everyone.