HbA₁c / Fasting Glucose Correlation

The calculator’s fasting-glucose estimate uses the heuristic HbA₁c (%) ≈ 2.6 + 0.03 × FPG (mg/dL). This is not a directly published regression — it was derived by inverting the ADAG trial’s HbA₁c-to-estimated-average-glucose (eAG) equation under a steady-state assumption that fasting plasma glucose (FPG) approximates eAG. Treat it as a rough estimate, not a clinical-grade result; a subsequent study found the FPG–eAG relationship is only moderately correlated and weakens further at lower glucose levels.

• Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ; A1c-Derived Average Glucose (ADAG) Study Group. Translating the A1C Assay Into Estimated Average Glucose Values. Diabetes Care. 2008;31(8):1473–1478. doi:10.2337/dc08-0545. PMID: 18540046. pubmed.ncbi.nlm.nih.gov/18540046 — source of the original eAG/HbA₁c regression equation that was inverted to build this heuristic.
• Kim HY, Lee SY, Suh S, Kim JH, Lee MK, Park HD. The relationship between estimated average glucose and fasting plasma glucose. Clin Chem Lab Med. 2013;51(11):2195–2200. doi:10.1515/cclm-2013-0045. PMID: 24057595. pubmed.ncbi.nlm.nih.gov/24057595 — the correlation between FPG and eAG this heuristic leans on, including its documented limitations.

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