Blood glucose is reported in milligrams per decilitre in the United States and in millimoles per litre almost everywhere else. To convert, divide mg/dL by 18 to get mmol/L, or multiply mmol/L by 18 for mg/dL. This tracker stores everything internally and converts on display, so switching units never loses data.
Why context is the most important field
A reading of 140 mg/dL (7.8 mmol/L) is unremarkable an hour after lunch and significant after an overnight fast. For diagnosis, commonly used thresholds are a fasting glucose of 100–125 mg/dL (5.6–6.9 mmol/L) for prediabetes and 126 mg/dL (7.0 mmol/L) or above, confirmed on a second occasion, for diabetes. For people already managing diabetes, many non-pregnant adults are given a pre-meal target of 80–130 mg/dL (4.4–7.2 mmol/L) and a peak after meals below about 180 mg/dL (10.0 mmol/L) — but individual targets vary widely, and yours come from your clinician.
How to measure properly
Wash your hands with warm water and dry them; alcohol wipes left wet, or traces of fruit sugar, both distort results. Use the side of the fingertip rather than the pad, and rotate fingers. Check that your strips are in date and coded to your meter. For a fasting reading, take it before eating, drinking anything but water, or taking morning medicines.
What changes it besides food
Illness and infection raise glucose, sometimes dramatically. So do corticosteroids, some antipsychotics, thiazide diuretics and decongestants. Poor sleep and psychological stress raise it through cortisol. Exercise usually lowers it, though intense effort can raise it briefly. Alcohol can cause delayed lows, particularly overnight. The dawn phenomenon — a rise in the early morning driven by normal hormone release — explains many otherwise puzzling fasting numbers.
Lows are the urgent direction
Below 70 mg/dL (3.9 mmol/L) is hypoglycaemia. The standard response is 15 grams of fast-acting carbohydrate, wait 15 minutes, and re-test. Below 54 mg/dL (3.0 mmol/L) is clinically significant and needs prompt treatment. Confusion, inability to swallow safely, seizure or unconsciousness is an emergency requiring glucagon and emergency services.