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eMedicine Journal
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Pediatrics
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Nephrology
Renal Glucosuria Synonyms, Key Words, and Related Terms: renal glucosuria, renal glycosuria, glucose in urine, Fanconi syndrome, cystinosis, Wilson disease, hereditary tyrosinemia, oculocerebrorenal syndrome, Lowe syndrome, hyperglycemia, diabetes mellitus, hypophosphatemic rickets, dehydration, short stature, Kayser-Fleischer ring |
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 | AUTHOR INFORMATION | Section 1 of 11    |
Authored by Leonard G Feld, MD, PhD, MMM, Chairman of Pediatrics, Carolinas Medical Center; Chief Medical Officer, Levine Children's Hospital, Carolinas Healthcare System
Leonard G Feld, MD, PhD, MMM, is a member of the following medical societies: American Academy of Pediatrics, American College of Physician Executives, American Heart Association, American Physiological Society, American Society of Nephrology, American Society of Pediatric Nephrology, American Society of Transplant Surgeons, Eastern Society for Pediatric Research, International Society of Nephrology, Juvenile Diabetes Foundation International, National Kidney Foundation, Society for Experimental Biology and Medicine, and Society for Pediatric Research
Edited by Laurence Finberg, MD, Clinical Professor, Department of Pediatrics, University of California at San Francisco and Stanford University; Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine.com, Inc; Luther Travis, MD, William W Glauser Professor of Pediatrics and Pediatric Nephrology, Department of Pediatrics, Divisions of Nephrology and Diabetes, University of Texas Medical Branch and Children's Hospital; Howard Trachtman, MD, Program Director, Pediatrics Research, Schneider Children's Hospital, Professor, Department of Pediatrics, Division of Nephrology, Albert Einstein College of Medicine; and Craig B Langman, MD, Professor, Department of Pediatrics, Northwestern University School of Medicine; Head, Division of Kidney Diseases, Children's Memorial Hospital of Chicago
| Author's Email: | Leonard G Feld, MD, PhD, MMM |  |
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| Editor's Email: | Laurence Finberg, MD |
eMedicine Journal, May 8 2006, VOLUME 7,
Number 5
| INTRODUCTION | Section 2 of 11  |
Background: Renal glucosuria is the excretion of glucose in the urine in detectable amounts at normal blood glucose concentrations or in the absence of hyperglycemia. In general, renal glucosuria is a benign condition and does not require any specific therapy. Glucosuria may be associated with tubular disorders such as Fanconi syndrome, cystinosis, Wilson disease, hereditary tyrosinemia, or oculocerebrorenal syndrome (Lowe syndrome).
Pathophysiology: Glucose is freely filtered by the glomerulus with a fractional excretion of less than 0.1%. Adults excrete about 65 mg of glucose per day. Reabsorption of glucose occurs predominantly on the brush border membrane of the convoluted segment of the proximal tubule. Glucose enters the tubular cells by an active carrier-mediated transport process, which is sodium dependent, and exits via the basolateral membrane by facilitated diffusion by a glucose transporter, which is sodium independent.
The sodium/glucose cotransporter is part of the SGLT1 group of sodium cotransport proteins. The human intestinal SGLT1 has been localized to chromosome 22. SGLT1 is found in the straight segment of the proximal tubule. The other cotransporter is SGLT2, which is expressed in the S1 segment of the proximal tubule and is localized to chromosome 6. The facilitative glucose transporters have isoforms GLUT 1-5. GLUT2 mainly is associated with glucose transport in the convoluted portion of the proximal tubule. In segments with high reabsorptive rates (S1 and S2 segments), the carrier is high capacity, low affinity. At birth, a high-affinity low-capacity pathway also exists to compensate for the reduced activity of the high-capacity low-affinity pathway.
Glucose reabsorption is age dependent. In premature infants of less than 30 weeks’ gestation, glucosuria is quite common because the filtered load of glucose delivered to the kidney often is too high for the immature nephron to handle. Glucosuria normally occurs when the plasma glucose content is above 300 mg/dL, but some glucose may be seen in the urine at plasma glucose levels as low as 150 because there is a great deal of variability in the glucose-handling capacity of individual nephrons. This variability arises from variation in the length of the proximal tubule and differences in glomerular size and location.
Tubular maximum for glucose (Tm glucose, mg/min/1.73 m2) corrected for the glomerular filtration rate (GFR) does not vary as a function of age. Tm glucose/GFR (mg/mL) presents as follows:
The Tm glucose for children expressed in mg/min/1.73 m2 is as follows:
Frequency:
Mortality/Morbidity: Renal glucosuria is a benign condition. However, morbidity is significant in Fanconi syndrome, Lowe syndrome, and cystinosis (see Differentials).
| CLINICAL | Section 3 of 11 |
History: Medical history offers no clues for either primary or benign renal glucosuria. In cases associated with combined tubular defects or hyperglycemia (ie, diabetes mellitus), history is specific to the disease or syndrome.
Renal glucosuria is first noted on routine urinalysis. In cases of glucosuria associated with tubular disorders, a history of growth failure, polyuria, polydipsia, or dehydration may exist.
Physical: No physical examination findings are relevant to renal glucosuria, unless associated with a secondary cause (eg, Fanconi syndrome, diabetes mellitus).
In cases associated with tubular disorders, signs or symptoms may include hypophosphatemic rickets, dehydration, short stature, muscle hypotonia, or ocular changes of cataracts or glaucoma (Lowe syndrome) or Kayser-Fleischer ring (Wilson disease).
Causes: The renal abnormality is specific to glucose and not other monosaccharides. The inheritance pattern is autosomal recessive, although autosomal dominance has been reported. Glucosuria can be divided into 3 clinical scenarios, as follows:
| DIFFERENTIALS | Section 4 of 11 |
Cystinosis
Diabetes Mellitus, Type 1
Fanconi Syndrome
Oculocerebrorenal Dystrophy (Lowe Syndrome)
Wilson Disease
Other Problems to be Considered:
| WORKUP | Section 5 of 11 |
Lab Studies:
| TREATMENT | Section 6 of 11 |
Medical Care: Benign renal glucosuria is a self-limiting process and requires no special medical care. If other associated findings suggest tubular disorders, then other interventions are required.
Consultations: Consultation with a pediatric nephrologist may be appropriate.
Diet: No special dietary instructions are required. In a very rare case of extremely large amounts of urinary glucose, glucose or another carbohydrate may be required during episodes of great physical activity to prevent hypoglycemia.
| MEDICATION | Section 7 of 11 |
No treatment is required for benign renal glucosuria.
| FOLLOW-UP | Section 8 of 11 |
Further Outpatient Care:
Prognosis:
Patient Education:
| MISCELLANEOUS | Section 9 of 11 |
Medical/Legal Pitfalls:
| TEST QUESTIONS | Section 10 of 11 |
CME Question 1: A 3-year-old girl is found to have glucosuria on an annual routine evaluation. Which of the following is the most appropriate test?
A: Fasting serum glucose concentration
B: Serum creatinine
C: Renal ultrasound
D: 24-hour urine glucose collection
E: Venous blood gas
The correct answer is A: The first step in the evaluation process is to rule out hyperglycemic causes of renal glucosuria (eg, diabetes mellitus).
CME Question 2: Which of the following is not included in the differential diagnosis of renal glucosuria?
A: Fanconi syndrome
B: Diabetes mellitus
C: Intestine malabsorption of glucose and galactose
D: Interstitial nephritis
E: Diabetes insipidus
The correct answer is E: Diabetes insipidus is a defect in water handling by the kidney from a central defect in the secretion of antidiuretic hormone (ADH) or the inability of the kidney to respond to ADH.
Pearl Question 1 (T/F): Renal glucosuria has an excellent prognosis.
The correct answer is True: In the absence of hyperglycemia or other tubular abnormalities, renal glucosuria has an excellent prognosis.
Pearl Question 2 (T/F): The primary treatment of renal glucosuria is dietary supplementation.
The correct answer is False: Nearly all cases of renal glucosuria require no specific therapy. In very rare cases, some additional glucose is provided during very competitive athletic events.
Pearl Question 3 (T/F): A glycosylated hemoglobin concentration is used in the evaluation of renal glucosuria.
The correct answer is True: This test is useful to exclude diabetes mellitus. If the glycosylated hemoglobin concentration and the blood glucose concentration are normal, then evaluation for associated tubular abnormalities should be initiated.
Pearl Question 4 (T/F): Glucosuria may be associated with urinary losses of phosphorus and bicarbonate.
The correct answer is True: Increased urinary excretion of phosphorus, amino acids, uric acid, and bicarbonate, in addition to glucose, is associated with Fanconi syndrome.
| BIBLIOGRAPHY | Section 11 of 11 |
| NOTE: |
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