Blood Sugar 42 mg/dl — Is It Dangerous? What to Do Now
Where 42 mg/dl sits — adjust to your situation
42 mg/dl as a fasting reading
Severely low (emergency)
A fasting reading this low is a medical emergency. It is far below the level your brain needs to work properly.
Fasting = no food for at least 8 hours, typically first thing in the morning. More on fasting readings.
42 mg/dl after eating
Severely low (emergency)
This is severely low at any time of day and is a medical emergency.
Guidelines measure 2 hours after the start of a meal. More on post-meal readings.
Measured right after exercise?
There is no official range for readings taken during or just after a workout, so the two classifications above do not apply to them. How exercise moves blood sugar.
How 42 mg/dl compares to a typical day
Typical day without diabetes; your reading is the horizontal line — below the band a typical day stays in.
What to do with a reading of 42 mg/dl
Take fast-acting sugar NOW (glucose tablets, juice, regular soda), then re-test in 15 minutes. If you cannot keep sugar down, feel faint, or someone finds you confused: call 911 (US) or your local emergency number.
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Questions about 42 mg/dl
Is 42 mg/dl blood sugar normal?
It depends on when you measured. Fasting, 42 mg/dl is severely low (emergency) (normal fasting range: 70–99 mg/dl). Two hours after a meal it is severely low (emergency) (normal post-meal range: 70–139 mg/dl).
What is 42 mg/dl in mmol/L?
42 mg/dl equals 2.3 mmol/L. Divide mg/dl by 18 to convert (used in the UK, Canada, Australia and most of Europe).
How accurate is a home reading of 42 mg/dl?
Home meters are allowed an error of ±15 mg/dl below 100 mg/dl and ±15 % from 100 up (ISO 15197), so a displayed 42 can correspond to a true value anywhere from 27 to 57 mg/dl. If you have symptoms, treat it as a low now; if you feel fine, wash and dry your hands and recheck.
BloodSugarEasy — blood sugar reading report
Reading: 42 mg/dl (2.3 mmol/L)
Fasting classification: Severely low (emergency) · After-meal classification: Severely low (emergency)
Reference: ADA criteria, reviewed 2026-08-21 · https://bloodsugareasy.com/blood-sugar-42/
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