Lactose Tolerance Test

CPT: 82951; 82952(x2)
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Test Details

Synonyms

  • Lactose Consumption Test

Test Includes

Fasting, 30-, 60-, 90-, and 120-minute glucose measurements

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.

Specimen Requirements

Specimen

Plasma

Volume

Full tube for each sample

Minimum Volume

1 mL each tube

Container

Gray-top (sodium fluoride) tube

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.

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

Causes for Rejection

Gross elevation of fasting blood glucose; improper labeling

Clinical Information

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 011593 Glucose 1 mg/dL 12638-3
046300 Lactose Tolerance Test 011601 Glucose 2 mg/dL 12648-2
046300 Lactose Tolerance Test 011619 Glucose 3 mg/dL 26777-3
046300 Lactose Tolerance Test 011627 Glucose 4 mg/dL 26778-1
046300 Lactose Tolerance Test 011635 Glucose 5 mg/dL 26779-9
046300 Lactose Tolerance Test 011648 Comment: N/A
046300 Lactose Tolerance Test 103656 Lactose Tolerance Test N/A

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