High Blood Sugar: When to Worry
Reviewed by CDE Mehandi Sharma · Updated
High blood sugar is the everyday reality of diabetes, so the useful skill is telling an ordinary high from one that needs attention today.
A single reading above your target after a heavy meal is information. It tells you something about that meal. It is not an emergency and it does not need a panicked response.
What deserves attention is a pattern — readings running high for several days, especially with symptoms returning: heavy thirst, passing urine often, tiredness, blurred vision. That usually means your treatment needs reviewing, and it is worth a call rather than waiting for a scheduled appointment.
What needs same-day help is a high reading with any of these: vomiting, trouble breathing, drowsiness or confusion, or ketones present in a urine or blood test. Testing for ketones is advised when you are unwell, and particularly when your blood sugar is 240 mg/dL or above.
Common reasons for an unexplained run of highs: an infection brewing (see sick days), a missed or wrong dose, steroid medicines prescribed for something else, or expired or heat-damaged test strips giving you wrong numbers.
Do not try to correct a high with extra doses of your own accord. That is how lows happen a few hours later.