Renal glucosuria is the excretion of glucose in the urine in the presence of normal plasma glucose levels.
Renal glucosuria can be inherited. This form usually involves a reduction in the glucose transport maximum (the maximum rate at which glucose can be resorbed) and subsequent escape of glucose in the urine. The inherited disorder is usually transmitted as an incompletely recessive trait (heterozygotes have modest glucosuria).
Renal glucosuria may occur without any other abnormalities of renal function or as part of a generalized defect in proximal tubule function (Fanconi syndrome). It also may occur with various systemic disorders, including cystinosis, Wilson disease, hereditary tyrosinemia, and oculocerebrorenal syndrome (Lowe syndrome).
Renal glucosuria is asymptomatic and without serious sequelae. However, if there is an associated generalized defect in proximal tubular function, symptoms and signs may include hypophosphatemic rickets, volume depletion, short stature, muscle hypotonia, and ocular changes of cataracts or glaucoma (oculocerebrorenal syndrome) or Kayser-Fleischer rings (Wilson disease). With such findings, transport defects other than glucosuria should be sought.
The disorder is typically initially noted on routine urinalysis.
Diagnosis is based on finding glucose in a 24-h urine collection (when the diet contains 50% carbohydrate) in the absence of hyperglycemia (serum glucose < 140 mg/dL). To confirm that the excreted sugar is glucose and to exclude pentosuria, fructosuria, sucrosuria, maltosuria, galactosuria, and lactosuria, the glucose oxidase method should be used for all laboratory measurements. Some experts require a normal result on an oral glucose tolerance test for the diagnosis.