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Synonyms
- Lactose Consumption Test
Test Includes
Fasting, 30-, 60-, 90-, and 120-minute glucose measurements
Expected Turnaround Time
Within 1 day
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Related Documents
Specimen Requirements
Specimen
Plasma
Volume
Full tube for each sample
Minimum Volume
1 mL each tube
Container
Gray-top (sodium fluoride) tube
Collection
Draw fasting sample prior to lactose administration.
Give lactose according to the following:
• Children up to 12 years: 2 g/kg body weight with a maximum of 50 g in 250 mL water.
• Adults: 50 g in 250 mL water Collect specimens at 30, 60, 90, and 120 minutes following lactose administration. Label each tube with the patient's name and time of drawing according to the following:
The first tube should be labeled with the "patient's name," "fasting," and the time of the draw.
The remaining four tubes should be labeled with the "patient's name" and the time of the draw.
Storage Instructions
Maintain specimen at room temperature.
Stability Requirements
Temperature | Period |
|---|---|
Room temperature | 14 days |
Refrigerated | 14 days |
Frozen | 14 days |
Freeze/thaw cycles | Stable x3 |
Patient Preparation
Patient should fast for eight hours before testing. No smoking or gum chewing allowed during test. Patient is encouraged to drink a moderate amount, one to two glasses of water during test. Patient should remain seated or in bed during test.
Causes for Rejection
Gross elevation of fasting blood glucose; improper labeling
Test Details
Use
Evaluate lactose intolerance, malabsorption syndromes. May be abnormal with Crohn's disease, small bowel resections, jejunitis, Giardia lamblia infestation, Whipple disease, and cystic fibrosis.
Methodology
Enzymatic
Additional Information
Lactose is a disaccharide digested by lactase. It yields glucose and galactose. The latter is converted to glucose by the liver after its absorption. Glucose is measured and it is the increase or lack of increase over the fasting specimen that is used for interpretation. A normal response will show a glucose increase >30 mg/dL over the baseline sample. Those with lactase deficiency will demonstrate bloating, cramps, and diarrhea and will show a glucose increase <20 mg/dL. Diabetic patients may have abnormal lactose tolerance curves due to abnormal carbohydrate metabolism and not necessarily due to lactose intolerance. Since 25% of normal individuals have flat glucose tolerance tests, it has been suggested that patients with flat lactose tolerance tests should also have a glucose tolerance test. Ethanol can prevent conversion of galactose to glucose by the liver; thus, blood or urine galactose can be measured.
Aftercare
Test may produce diarrhea and cramps.
References
Heyman MB; Committee on Nutrition. Lactose intolerance in infants, children, and adolescents. Pediatrics. 2006 Sep; 118(3):1279-1286.
Wu A. Tietz Guide to Laboratory Tests. 4th ed. Saunders/Elsevier; 2006.
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 046300 | Lactose Tolerance Test | 69555-1 | 011593 | Glucose 1 | mg/dL | 12638-3 |
| 046300 | Lactose Tolerance Test | 69555-1 | 011601 | Glucose 2 | mg/dL | 26777-3 |
| 046300 | Lactose Tolerance Test | 69555-1 | 011619 | Glucose 3 | mg/dL | 26778-1 |
| 046300 | Lactose Tolerance Test | 69555-1 | 011627 | Glucose 4 | mg/dL | 26779-9 |
| 046300 | Lactose Tolerance Test | 69555-1 | 011635 | Glucose 5 | mg/dL | 26780-7 |
| 046300 | Lactose Tolerance Test | 69555-1 | 011648 | Comment: | N/A |
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