Your small intestine produces an enzyme called lactase, which is responsible for breaking down the milk sugar lactose. If you are lactose intolerant, your small intestine does not produce sufficient amounts of lactase to break down lactose. Instead, milk sugar travels through your digestive system in its undigested form, causing uncomfortable symptoms like gas, bloating and diarrhea. Several laboratory test can be used to determine if you are lactose intolerant.
Blood Test
A lactose intolerance blood test begins with drinking a liquid solution that contains high levels of lactose. After the liquid has had time to travel through your digestive system and enter your bloodstream, in approximately two hours, a doctor will draw your blood and test the amount of glucose it contains. Normal digestion of lactose causes a rise in blood glucose levels. If your blood glucose levels do not rise significantly after ingesting the lactose solution, it indicates that your body does not digest lactose properly. A 30 mg/dL rise in blood glucose indicates that you digest lactose properly. According to Medline Plus, a 20 to 30 mg/dL rise is considered inconclusive. A rise in blood glucose lower than 20 mg/dL indicates that you do not digest lactose properly.
Hydrogen Breath Test
A hydrogen breath test involves drinking a liquid that contains high levels of lactose and then measuring the amount of hydrogen on your breath at predetermined intervals. Normally, your breath contains very small amounts of hydrogen. If you are lactose intolerant, the undigested lactose travels to your colon, where it reaches the bacteria that live there. These bacteria begin to ferment the lactose, creating hydrogen and other gases as a byproduct. Your small intestine absorbs these gases, which are eventually removed from your body through your lungs. If your breath contains high amounts of hydrogen, which Medline Plus defines as 12 parts per million, or ppm, over your pre-test value, it indicates that your body is not digesting and absorbing lactose properly.
Stool Acidity Test
A doctor may use a stool acidity test for infants and young children who cannot undergo other types of lactose intolerance testing. When undigested lactose moves through the colon, it creates acids, including lactic acid, as a byproduct. A stool acidity test measures the stool for these acids. The stool may also contain detectable amounts of glucose.
Considerations
You should not eat any foods or drink any liquids for at least 8 hours before lactose intolerance testing. Avoid any strenuous exercise as well. Strenuous exercise can lead to the accumulation of lactic acid in the muscles, which can be misinterpreted as lactose intolerance during lactose testing.
