When Your Blood Sugar Is Suddenly High

A single high reading is usually not an emergency. A run of them, or a high reading with certain symptoms, is a different matter.

First, check the obvious

• Was the test itself sound? Unwashed hands are the commonest cause of a falsely high reading — fruit or sweet chai on a fingertip is enough.
• Did you miss a dose, or take it late?
• Are you unwell? Fever and infection raise blood sugar even when you are eating less.
• Have you started a new medicine? Steroids in particular.
• Was there an obvious meal? Then retest before the next one rather than reacting now.

Repeat the test with washed, dry hands before doing anything else. If it is still high, drink water, keep taking your medicines, and check again in two to four hours rather than correcting repeatedly — stacking corrections is how a high becomes a low.

Get help the same day if

• You are vomiting or cannot keep fluids down.
• You have ketones, particularly above 1.5 mmol/L.
• You are breathing deeply, drowsy or confused, or your breath smells fruity.
• Readings stay high despite following your usual plan.

If you have Type 1 diabetes, test for ketones whenever a reading is well above target, not just when you feel unwell. More in high blood sugar: when to worry.