What Is a Lactose Tolerance Test?

Some people experience uncomfortable symptoms, such as bloating and cramps, after they consume milk or other dairy products. This is a condition called lactose intolerance, or lactose malabsorption. Nearly everyone is born with enough lactase, a type of enzyme that breaks down lactose, but over time lactase levels can become low, which causes the body to have an intolerance to lactose. If you or your gastroenterologist suspect lactose intolerance, they will order one of two tests: the hydrogen breath test or the lactose tolerance test. Both can offer a definite diagnosis of lactose intolerance. 

What Are the Symptoms of Lactose Intolerance, and Should I See a Doctor?

Lactose intolerance is not a serious condition and typically doesn’t cause further complications, however, the symptoms can be incredibly uncomfortable. Symptoms usually present within 30 minutes to 2 hours after ingesting dairy products and can include:

• Nausea
• Vomiting
• Bloating
• Gas
• Diarrhea
• Stomach cramps 

If you notice these symptoms regularly after you consume dairy products, you should consult your gastroenterologist. Many gastrointestinal disorders share the same symptoms, so you should see a doctor if they persist. Also, avoiding dairy puts you at risk of not getting enough calcium in your diet, so your physician can instruct you on how to eliminate or cut back on dairy safely.

What Is the Cause of Lactose Intolerance?

When we are born, we have an enzyme called lactase. Lactose is the sugar found in milk and dairy products. When someone without lactose intolerance consumes milk, the lactase enzyme breaks down lactose into glucose and galactose, which enter the bloodstream through the small intestine. Patients that have lactose intolerance are deficient in lactase, so lactose does not get digested properly. Undigested portions of lactose then enter the colon (large intestine), and the large intestine struggles to digest the lactose. This is what causes lactose intolerance symptoms. 

The main risk factor of lactose intolerance is age. Babies are rarely born without enough lactase, but as we age, levels can decrease. This means that an onset of lactose intolerance can occur at any time. Other risk factors include:

• Ethnicity. Lactose intolerance is more common in those of Asian, African, American Indian, or Hispanic descent. 
• Small intestine diseases. If you already have a digestive disorder of the small intestine, such as Crohn’s disease or celiac disease, this puts you at higher risk. 
• Prematurity. If you were born prematurely, you may have had a lower amount of lactase at birth, leading to lactose intolerance later in life. 
• Cancer treatments. Radiation and chemotherapy can change how your body digests lactose. 

How Is Lactose Intolerance Diagnosed?

Physicians use two primary tests to diagnose lactose intolerance: the hydrogen breath test or the lactose tolerance test. There is a third test for infants and young children, known as the stool acidity test. The most commonly used test is the hydrogen breath test, but the lactose tolerance test is used as well. 

How Is the Lactose Tolerance Test Performed?

To prepare for the test, your physician will ask you to fast for 8 to 12 hours before the test. You should let your doctor know if you are a smoker, as this can affect the test. Also, certain medications can affect your results, so let your doctor know about all medications and over-the-counter supplements you are taking. 

When you arrive at the lab or your doctor’s office, you will give a blood sample. Next, you’ll be asked to drink a beverage that contains lactose. You then wait for a period of time (usually two hours) as your body digests the lactose. After this time has passed, your blood is drawn and the sample is sent off to be evaluated. The test measures the amount of glucose in your blood after ingesting lactose. 

Normally, your body breaks down lactose into glucose and galactose, and these sugars are absorbed through the small intestine. A patient with lactose intolerance does not digest lactose properly and tries to break it down in the large intestine. Because the glucose is not absorbed into the bloodstream in a patient with lactose intolerance, the lower levels of glucose in the bloodstream indicate intolerance to lactose. 

What Are the Treatments for Lactose Intolerance?

If you discover you’re lactose intolerant, the first thing your physician will do is tell you to limit or avoid dairy, depending on the severity of your symptoms. If you need to avoid dairy completely, your physician will advise you on how to supplement with calcium. You can also add a liquid or powder lactase enzyme to milk to help break down the lactose when you do ingest dairy.  Most people with lactose intolerance can consume small amounts of dairy and experience no symptoms. Your gastroenterologist also may recommend supplementing with probiotics, particularly if you have another digestive condition. Probiotics can help ease symptoms of other conditions, such as irritable bowel syndrome (IBS), and may also help your body break down lactose.