Lactose Intolerance Test

Reviewed by: HU Medical Review Board | Last reviewed: June 2016. | Last updated: November 2019

Many patients with irritable bowel syndrome (IBS) notice their symptoms are exacerbated by dietary changes. A common dietary sensitivity is lactose intolerance, in which the body has difficulty digesting dairy products. Lactose is the sugar found in milk and other dairy products, and lactase is the enzyme produced by the intestines to digest lactose.1

During the diagnosis of IBS, physicians may recommend a lactose intolerance test. The lactose intolerance test can also help determine if a patient’s symptoms are indeed due to IBS or if the symptoms are solely due to the body’s inability to digest dairy. It is possible that a patient may have both lactose intolerance and IBS. Dietary intolerances, such as lactose intolerance, are present in about one-third of IBS patients.2

What is lactose intolerance?

Several symptoms of lactose intolerance are similar to IBS symptoms, such as:

However, digestive symptoms caused by lactose intolerance are usually experienced 30 minutes to two hours after ingesting dairy products.3 The symptoms may be more severe when a larger amount of dairy is consumed.1

Lactose intolerance is a common digestive condition in adults, and it is estimated that about 30 million American adults have some level of lactose intolerance by age 20.1

The recommended treatment for lactose intolerance is to limit or remove dairy products from the diet. Symptoms from lactose intolerance are often relieved when dairy products are eliminated from the diet. Dairy products include milk, cheese, sour cream, and ice cream. In addition, it is important to look at food labels, as several products contain milk or lactose as an ingredient.1

Some people with low lactase levels may find they can consume small amounts of milk and other dairy products without experiencing symptoms. There are also some milk products, such as goat’s milk, fermented milk products (yogurt), and aged cheeses, which may be easier to digest. The addition of lactase enzymes, in the form of a supplement taken with food, may also help some patients digest dairy and avoid the symptoms of lactose intolerance.1

How is the lactose intolerance test performed?

A lactose intolerance test measures the body’s reaction to the sugar lactose. The patient is given a liquid containing a high level of lactose. Two hours later, the patient’s blood is collected to measure the amount of glucose – the sugar that the body naturally creates from lactose. If the body’s glucose level doesn’t increase, it is determined that the body isn’t digesting and absorbing the lactose liquid properly.3

Additional tests to determine lactose intolerance include a lactose-hydrogen breath test and a stool pH test.1 A patient can also try an elimination diet, where dairy products are removed from the diet for several weeks to notice if the symptoms subside.4

Other tests for IBS

Because there is no single definitive test to determine if a patient has IBS, several tests are usually done to determine if a patient’s digestive symptoms are caused by IBS, as well as to eliminate other potential causes for the symptoms. Other tests in a diagnosis of IBS include a physical exam, symptom history, blood tests, a stool analysis, and occasionally a lower GI series (x-ray), a colonoscopy or a CT scan.

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