Blood Glucose Interpreter

Metformin lowers blood glucose by reducing hepatic glucose production and improving insulin sensitivity. If you are on metformin, your unmedicated glucose would likely be higher.

Insulin directly lowers blood glucose. Glucose readings on insulin therapy reflect the medicated state and the dosing regimen, not endogenous glucose control.

GLP-1 agonists (semaglutide, liraglutide, tirzepatide) lower both fasting and post-meal glucose, sometimes substantially. Trend readings over time matter more than any single value while titrating these medications.

SGLT2 inhibitors (empagliflozin, dapagliflozin) increase glucose excretion through urine. Watch ketones at this medication class, as euglycemic DKA is a known risk — elevated ketones with seemingly normal glucose.

Corticosteroids (prednisone, dexamethasone) elevate blood glucose, sometimes meaningfully. Expect higher readings while on a steroid course, with values returning toward baseline after taper.

If you are taking any of these medications, your readings reflect the medicated state. Discuss target ranges with your prescribing provider — what is “normal” for an untreated person may differ from your treatment target.

Formula

Blood glucose is measured directly from a blood sample (finger-stick meter, CGM, or lab venous draw), reported in mg/dL (US labs) or mmol/L (SI / international). No formula — the value is read off the meter or lab report. Conversion: 1 mmol/L ≈ 18.018 mg/dL.

Classification

Fasting (8+ hours, no food): Optimal <85, Healthy range 85–99, Elevated 100–125, Concerning ≥126 mg/dL. ADA diagnostic cutoff for diabetes is 126; clinical "pre-diabetic" range is 100–125.

1-hour post-meal: Optimal <140, Elevated 140–179, Concerning 180–219, Seek care ≥220 mg/dL.

2-hour post-meal: Optimal <120, Elevated 120–139, Concerning 140–179, Seek care ≥180 mg/dL. Two-hour readings are the standard for oral glucose tolerance testing.

Random: Likely normal <140, Elevated 140–179, Concerning 180–199, Seek care ≥200 mg/dL.

Known Limitations

A single reading is a snapshot — blood glucose fluctuates throughout the day in response to food, exercise, sleep, stress, and illness. For a fuller picture, pair this with HbA1c (2–3 month average), fasting insulin (insulin output context), and HOMA-IR (insulin resistance). Continuous glucose monitors (CGMs) reveal patterns that single readings hide. Strip-meter readings have ±10% variability; lab draws are more accurate but less timely. Hydration, recent caffeine, and acute stress can move readings 10–30 mg/dL transiently.

Sources

American Diabetes Association. Standards of Medical Care in Diabetes. Diabetes Care, updated annually. Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) Study Cooperative Research Group. NEJM, 2008. International Diabetes Federation. Postprandial Glucose Management Guidelines, 2011.