The most common diagnostic tests (performed on an outpatient basis at the hospital) measure the absorption of lactose in your child's digestive system include the following:
- Lactose tolerance test - This test measures the absorption of lactose in the digestive system. After fasting, your child drinks a liquid that contains lactose. The diarrheal stools are then tested for lactose for the next 24 hours. Undigested lactose fermented by bacteria in the colon creates lactic acid and other fatty acids, which can be detected in a stool sample, along with glucose as a result of unabsorbed lactose.
- Hydrogen breath test - Your child drinks a lactose-heavy beverage. Her breath is then analyzed at regular intervals to measure the amount of hydrogen. Undigested lactose in the colon is fermented by bacteria, resulting in the production of various gases, including hydrogen. When high levels of hydrogen are present in the breath, improper digestion of lactose is diagnosed.