Norm of Fructose Challenge Test
Lack of significant change in serum glucose, phosphorus, and magnesium concentrations after intravenous fructose administration. Lack of a decrease in serum glucose level after an oral fructose load. Normal plasma fructose level is <10 mg/dL or <6 mmol/L (SI units).
Usage of Fructose Challenge Test
The intravenous fructose challenge test and an oral fructose challenge test are used in the evaluation of several inherited disorders of fructose metabolism including essential fructosuria, hereditary fructose intolerance, and fructose-1,6-diphosphatase deficiency, and to aid in the diagnosis of steatohepatitis.
Description of Fructose Challenge Test
Fructose disorders all are inherited as autosomal recessive traits. Essential fructosuria is a clinically benign disorder. Fructose-1,6-diphosphatase deficiency is a clinically severe and often terminal illness in the newborn that is frequently diagnosed by clinical clues that do not involve fructose-loading tests. Hereditary fructose intolerance is a disorder, seen in children as well as adults, that is caused by a deficiency of fructose-1-phosphate aldolase. This condition, characterized by an aversion to sweet foods, may be diagnosed by use of the intravenous fructose challenge test. In this test, a weight-based dose of intravenous fructose is administered intravenously, and serial blood and urine samples are obtained.
Professional Considerations of Fructose Challenge Test
Consent form IS required.
Profound hypoglycemia is likely to occur in clients with hereditary fructose intolerance.
Known fructose intolerance. Ancillary medical conditions in which hypoglycemia would impose unacceptable risk to the client (certain forms of cardiac and neurologic disease).
- See Client and Family Teaching.
- Insert an indwelling intravenous catheter for the administration of fructose, for obtaining blood samples, and if the emergent administration of intravenous glucose is needed.
- Insert an indwelling urinary catheter if urine samples will be measured.
- Obtain 10 red-topped, red/gray-topped, or gold-topped tubes.
- Obtain blood glucose monitoring machine and associated supplies.
- Obtain parenteral glucose solution (D50W).
- Have emergency equipment readily available.
- Just before beginning the procedure, take a “time out” to verify the correct client, procedure, and site.
- The client is positioned recumbent.
- Draw a 7-mL baseline blood sample for serum glucose, fructose, potassium, phosphorus, magnesium, and urate determination.
- If urine testing will be included, collect a 2-hour baseline urine sample for urate, phosphorus, lactate, alanine, magnesium, and fructose determination.
- Administer 200 mg/kg (body weight) of 20% fructose solution intravenously over a 1-minute period for children or over a 2-minute period for adults.
- Repeat step 2 above, drawing the blood sample immediately after the injection and then at 5, 10, 15, 20, 30, 45, 60, 90, and 120 minutes after the fructose infusion.
- Urine measurements of fructose, lactate, alanine, magnesium, and phosphorus are occasionally performed during the fructose challenge test.
- Serum glucose is monitored frequently during the test with cutaneous blood glucose monitoring.
- Write beginning and ending times of each urine collection on the laboratory requisition.
- Perform cutaneous blood glucose measurement frequently and observe closely for signs of hypoglycemia for several hours after the test.
- Discontinue urinary catheter.
- Discontinue intravenous catheter once it is determined that hypoglycemia is no longer a risk.
Client and Family Teaching
- Consume a diet free of fructose and sucrose during the 3 weeks before the test.
- This test is needed to help diagnose hereditary fructose intolerance. This is a condition in which modifying your diet to reduce fructose in your food can improve your prognosis.
- This test may cause you to feel hypoglycemic. If this occurs, it will be quickly treated.
Factors That Affect Results
- Accurately timed and labeled serum and urine samples are essential.
- Abnormally low fructose levels may result if the urine specimen is not tested when it is still fresh.
- Timed studies of this type are often best performed in special diagnostic areas where the personnel are familiar with the diagnostic procedure.
- Hereditary fructose intolerance is associated with hypoglycemia after intravenous fructose administration. Other phenomena observed in these clients during the test include a rise in serum magnesium and uric acid levels, a fall in serum phosphorus level, and a decrease in urine phosphorus excretion after the fructose administration.
- Infants fed with a sucrose-containing formula that is hydrolyzed to fructose will exhibit more severe symptoms than breast-fed infants, who are usually asymptomatic, because lactose is not catabolized by the fructose enzyme.
- Liver biopsy specimens examined for metabolites of fructose may also be used for diagnosis of hereditary fructose intolerance.
- Treatment for hereditary fructose intolerance is a fructose-free and sucrose-free diet.