{
  "packVersion": "2026.07",
  "formulas": [
    {
      "id": "eag-nathan-2008",
      "label": "Estimated average glucose (ADAG / Nathan)",
      "expression": "eAG (mg/dL) = 28.7 x A1C - 46.7",
      "katex": "\\mathrm{eAG}_{\\mathrm{mg/dL}} = 28.7 \\times \\mathrm{A1C} - 46.7",
      "source": {
        "label": "Nathan et al., Diabetes Care 2008 (ADAG study)",
        "url": "https://doi.org/10.2337/dc08-0545",
        "citation": "Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ, for the A1c-Derived Average Glucose (ADAG) Study Group. Translating the A1C Assay Into Estimated Average Glucose Values. Diabetes Care. 2008;31(8):1473-1478."
      },
      "verifiedDate": "2026-07-30",
      "status": "verified",
      "uncertainty": "A population regression: in the ADAG study, individuals at the same A1C had meaningfully different mean glucose. The A1C assay itself carries about +/- 0.5 percentage points under NGSP certification.",
      "provenance": "primary",
      "notes": "The mmol/L figure shown on this site is converted from this mg/dL result using the glucose molar factor 18.0182, so the two displayed numbers are consistent with each other. The paper also publishes a separate mmol regression (1.5944 x A1C - 2.5944) which differs by up to about 0.07 mmol/L; see /methodology."
    },
    {
      "id": "gmi-bergenstal-2018",
      "label": "Glucose Management Indicator (GMI)",
      "expression": "GMI (%) = 3.31 + 0.02392 x mean glucose (mg/dL)",
      "katex": "\\mathrm{GMI}\\,\\% = 3.31 + 0.02392 \\times \\overline{G}_{\\mathrm{mg/dL}}",
      "source": {
        "label": "Bergenstal et al., Diabetes Care 2018",
        "url": "https://doi.org/10.2337/dc18-1581",
        "citation": "Bergenstal RM, Beck RW, Close KL, Grunberger G, Sacks DB, Kowalski A, Brown AS, Heinemann L, Aleppo G, Ryan DB, Riddlesworth TD, Cefalu WT. Glucose Management Indicator (GMI): A New Term for Estimating A1C From Continuous Glucose Monitoring. Diabetes Care. 2018;41(11):2275-2280."
      },
      "verifiedDate": "2026-07-30",
      "status": "verified",
      "uncertainty": "GMI and a laboratory A1C commonly differ in the same person; the paper reports that difference is often substantial and is itself informative rather than an error.",
      "provenance": "primary"
    },
    {
      "id": "a1c-ifcc-ngsp",
      "label": "NGSP percent to IFCC mmol/mol",
      "expression": "IFCC (mmol/mol) = (NGSP % - 2.15) x 10.929",
      "source": {
        "label": "NGSP - IFCC standardisation and the NGSP/IFCC master equation",
        "url": "https://ngsp.org/ifccngsp.asp",
        "citation": "National Glycohemoglobin Standardization Program. IFCC standardization of HbA1c and the NGSP-IFCC master equation. NGSP, accessed 2026."
      },
      "verifiedDate": "2026-07-30",
      "status": "verified",
      "uncertainty": "The master equation is periodically re-derived from network comparison data; treat converted values as approximate.",
      "provenance": "primary",
      "notes": "Needed because UK, Australian and much of European lab reporting uses IFCC mmol/mol rather than NGSP percent."
    },
    {
      "id": "a1c-assay-tolerance-ngsp",
      "label": "A1C assay tolerance (NGSP certification)",
      "expression": "certified assays agree with the reference method within about +/- 0.5 percentage points",
      "source": {
        "label": "NGSP - certification criteria for A1C methods",
        "url": "https://ngsp.org/certified.asp",
        "citation": "National Glycohemoglobin Standardization Program. Certification criteria for hemoglobin A1c methods. NGSP, accessed 2026."
      },
      "verifiedDate": "2026-07-30",
      "status": "verified",
      "uncertainty": "This is the certification limit for the method, not a confidence interval for one person's result.",
      "provenance": "primary",
      "notes": "Used to tell readers, honestly, that a small change between two A1C results may be the assay rather than anything about them."
    }
  ]
}