Hyperglycaemia symptoms often mirror the warning signs of undiagnosed diabetes: excessive thirst, passing large amounts of urine, fatigue, blurred vision, dry mouth, and difficulty concentrating. Mild rises may cause no symptoms at all, which is why monitoring matters.
Persistently high blood sugar over time raises the risk of complications affecting the eyes, kidneys, nerves, and heart, so sustained highs should be reviewed with your care team.
Very high blood sugar can become dangerous. Warning signs that need urgent attention include nausea and vomiting, abdominal pain, deep or rapid breathing, a fruity smell on the breath, drowsiness, or confusion. These can indicate diabetic ketoacidosis or a severe hyperglycaemic emergency, seek urgent care or call your local emergency number immediately.