Signs and Symptoms of Hyperglycemia
Marked hyperglycemia causes a characteristic constellation of symptoms including frequent urination (polyuria), excessive thirst (polydipsia), blurred vision, fatigue, and recurring infections. 1
Classic Osmotic Symptoms
The hallmark symptoms of hyperglycemia result from osmotic effects of elevated blood glucose:
- Polyuria (frequent urination) occurs when blood glucose exceeds the renal threshold (typically around 180 mg/dL or 10 mmol/L), causing glucose to spill into urine and draw water with it through osmotic diuresis 1, 2
- Polydipsia (excessive thirst) develops as a compensatory response to fluid losses from polyuria 1
- Blurred vision results from osmotic changes in the lens of the eye due to elevated glucose levels 1
Metabolic and Constitutional Symptoms
- Fatigue and weakness are prominent features as cells cannot effectively utilize glucose despite its abundance in the bloodstream 1
- Weight loss may occur despite normal or increased appetite, particularly in uncontrolled diabetes, as the body breaks down fat and muscle for energy 3
- Recurring infections, particularly urinary tract infections and skin infections, occur more frequently due to impaired immune function in hyperglycemic states 1
Gastrointestinal Manifestations
- Nausea and vomiting can develop when blood glucose levels remain severely elevated for extended periods 4
- Hyperglycemia directly slows gastric emptying and increases perception of gastrointestinal symptoms including nausea and abdominal pain, even at blood glucose levels as low as 8 mmol/L (144 mg/dL) 4
Warning Signs of Severe Hyperglycemia
When hyperglycemia progresses to dangerous levels, additional symptoms emerge:
- Diabetic ketoacidosis (DKA) presents with nausea, vomiting, abdominal pain, and high levels of ketones in blood and urine—this is a life-threatening emergency requiring immediate medical attention 4
- Altered mental status, confusion, or decreased level of consciousness indicate severe metabolic derangement 5
- Fruity-smelling breath (from acetone) may be present in ketoacidosis 4
Important Clinical Caveats
- Symptoms alone are poor predictors of the actual degree of hyperglycemia—objective blood glucose testing is essential for accurate assessment 4
- The presence of glycosuria (glucose in urine) indicates blood glucose has exceeded the renal threshold, suggesting poor glycemic control 2
- When nausea and vomiting accompany hyperglycemia, immediately check for ketones as this combination may signal impending or established DKA 4
- Patients taking SGLT2 inhibitors are at increased risk for euglycemic DKA and should stop medication immediately if symptoms develop 4