What does it mean when you have glucose in your urine, or glycosuria?

Glucose in Urine (Glycosuria): Meaning and Implications

Glycosuria occurs primarily when blood glucose levels exceed the renal threshold (approximately 180 mg/dL), causing glucose to spill into the urine, most commonly indicating diabetes mellitus or poor glycemic control. 1

Causes of Glycosuria

Glycosuria can result from several conditions:

Primary Causes

• Diabetes Mellitus: The most common cause of glycosuria, occurring when blood glucose exceeds the renal threshold 1
• Renal Tubular Dysfunction: Impaired glucose reabsorption in the proximal tubules 1, 2
• Familial Renal Glycosuria: A rare genetic disorder affecting the sodium-glucose co-transporter 2 (SGLT2), causing glucose excretion despite normal blood glucose levels 2, 3

Secondary Causes

• Medications: Certain drugs like SGLT-2 inhibitors (intentionally), corticosteroids, some antibiotics, and diuretics 1, 4
• Pregnancy: Due to altered renal threshold during gestation 1
• Stress-induced hyperglycemia: From severe illness, trauma, or surgery 1

Clinical Significance

Diabetes Mellitus

• Glycosuria is a classic sign of uncontrolled diabetes, appearing alongside symptoms like polyuria, polydipsia, weight loss, and blurred vision 1
• Finding glucose in urine should prompt evaluation of blood glucose levels to confirm or rule out diabetes 5
• In known diabetics, glycosuria may indicate inadequate glycemic control 1

Non-Diabetic Causes

• Familial renal glycosuria presents with persistent glycosuria despite normal blood glucose levels 2
• The severity varies from mild to severe (type 0) based on the degree of reduction in glucose threshold and maximal tubular reabsorption 3

Diagnostic Approach

When glycosuria is detected:

1. Measure blood glucose levels to differentiate between hyperglycemia-induced and renal causes 1
2. Consider HbA1c testing to assess glycemic control over the previous 2-3 months 5
3. Evaluate for other markers of tubular dysfunction if blood glucose is normal 1
4. Consider genetic testing for suspected familial renal glycosuria 2

Clinical Pearls and Pitfalls

• Important caveat: The American Diabetes Association does not recommend urine glucose testing for routine diabetes care, as it has been replaced by direct blood glucose monitoring 1
• Pitfall to avoid: Urine glucose testing cannot distinguish between normal blood glucose and hypoglycemia, as both result in absence of glycosuria 1
• Key consideration: The renal threshold for glucose varies between individuals due to differences in renal glucose transporters, kidney function, and insulin resistance 1
• Clinical insight: Finding glycosuria should prompt referral to appropriate specialists for proper evaluation and management of potential diabetes 5
• Late complication awareness: Prolonged glycosuria may eventually lead to glomerular damage and albuminuria as diabetic nephropathy progresses 6