Lactose, the primary sugar in milk, normally digests in the small intestine with the help of an enzyme called lactase. Since lactose intolerant individuals do not produce enough of the lactase enzyme, their bodies cannot digest lactose properly. The undigested food passes into the large intestine or colon where bacteria break it down, causing symptoms such as gas, flatulence, abdominal pain, nausea and diarrhea. If your healthcare provider needs to rule out other conditions such as irritable bowel syndrome, she may order a lactose-tolerance test.
Lactose Intolerance
Lactose intolerance, a condition more common in adults of African-American, Hispanic, American Indian and Asian descent, often occurs as the result of aging, MayoClinic.com reports. Some infants have lactose intolerance as a result of a rare genetic defect or premature birth. Lactose-intolerance symptoms may be mild to severe and occur 30 minutes to 2 hours after ingesting dairy products. Treatment includes limiting or avoiding foods that contain lactose or taking a lactase enzyme medication when eating dairy products.
Testing of Older Children and Adults
Two types of lactose-tolerance tests measure the body's reaction to drinking a lactose-rich liquid. The hydrogen breath test, the most common test for lactose intolerance and malabsorption, involves blowing into a balloon-like container at regular intervals after drinking the lactose dose. An increase in hydrogen level demonstrates increased gas production because poorly absorbed lactose is reaching the intestines. Less commonly, blood-glucose tests can measure the body's ability to digest and absorb the glucose dose.
Side Effects of Testing
Gastrointestinal symptoms, the most common side effects of lactose intolerance testing, include gas, flatulence, abdominal pain and diarrhea related to the high-dose lactose liquid used for the blood and breath tests. The customary dose of 20 g to 25 g of lactose exceeds the amount that most patients consume throughout a normal day by drinking milk and eating other dairy products. Therefore, patients are more likely to react to the high-lactose liquid than to the smaller amounts normally consumed during a meal.
Expert Viewpoint
Testing with 25 g of lactose causes symptoms in patients who may not react to a lower dose, states Fiorenza Argnani, M.D., in a report published in the February 2003 issue of the "World Journal of Gastroenterology." Among 65 patients who tested positive after a 25 g dose, gaseousness occurred 36 times, abdominal pain 34 times, flatulence 16 times and diarrhea occurred eight times. When retested with 12.5 g of lactose, the same group experienced gaseousness three times, abdominal pain once and flatulence three times. Since treatment for lactose intolerance includes a restrictive diet, Argnani suggests that healthcare providers test patients with the lower dose of lactose to avoid false positive results.
Testing of Infants and Small Children
The lactose dose used for blood and breath tests can be dangerous for infants and small children so clinicians use the stool-acidity test for these age groups. The test measures the amount of lactic acid in a stool sample to determine if undigested lactose reaches the colon. Since the test doesn't involve administering a dose of lactose, no side effects have been reported.
References
- MedlinePlus: Lactose Intolerance Tests
- Mayo Clinic: Lactose Intolerance
- "Practical Gastroenterology"; Lactose Intolerance: Considerations for the Clinician; Stacey McCray, R.D.; February 2003
- "World Journal of Gastroenterology"; Hydrogen Breath Test for the Diagnosis of Lactose Intolerance: Is the Routine Sugar Load the Best One?; Fiorenza Argnani, M.D., et al.; October 2008
