Lactose Intolerance

Diagnosis

It's possible you have lactose intolerance if your symptoms improve dramatically when you avoid lactose. A trial period of a lactose-free diet is usually all that is needed to make the diagnosis of lactose intolerance.

In some cases, your doctor will want to do tests to confirm the diagnosis.

One test to confirm the diagnosis is the lactose breath hydrogen test. The test is painless and noninvasive. You cannot eat food for several hours beforehand.

You begin the test by drinking a liquid that contains lactose. Your breath is then sampled for hydrogen over a few hours. Normally, very little hydrogen is detected in your breath. However, if you have lactose intolerance, the bacteria in your intestine will break the undigested lactose into hydrogen, which then moves through the bloodstream to your lungs and is exhaled. You will be diagnosed with lactose tolerance if higher-than-normal hydrogen levels are detected during this test.

An alternative test is the lactose tolerance test. You take the test on an empty stomach, and you begin by drinking a lactose solution. This test measures blood sugar levels at selected intervals over a few hours to determine your ability to digest lactose. If the lactose is digested, it produces glucose, which elevates your blood sugar level. You will be diagnosed with lactose intolerance if your blood sugar levels do not change during this test.

A significant number of people who have symptoms that suggest lactose intolerance will have normal results on diagnostic tests. Similar symptoms (but normal results on the tests) can be caused by fructose, sorbitol, or other sugars that are not easily digested in the small intestine. Similar symptoms can also result from irritable bowel syndrome.

Expected Duration

People who develop lactose intolerance as a result of gastroenteritis or another insult to digestion can recover completely when the intestinal problem is treated. This may take several weeks to months.

When lactose intolerance is genetic, the condition is permanent. However, people can avoid symptoms by avoiding foods that contain lactose (essentially, dairy products) or by eating them in moderation. In addition, commercially-prepared forms of the lactase enzyme are available (for example, Lactaid). These replacement enzymes usually do not relieve the symptoms entirely.