Lactose Tolerance Test

Test ID: 

703015

CPT code:

82951, 82952 (x2)

Synonyms:

Lactose Consumption Test

Clinical 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.

Test 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 Type:

Plasma

Requested Volume: 

Full tube for each sample

Minimum Volume: 

1 mL each tube

Container Type: 

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

Rejection Criteria

Gross elevation of fasting blood glucose; improper labeling

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