Diagnosing Lactose Intolerance

The most accurate way to diagnose Lactose Intolerance is the hydrogen breath test. The patient drinks about 50 grams of lactose (milk sugar) dissolved in water and on an empty stomach. The hydrogen content of the breath is measured both before and during the three hours after consuming the lactose.

How does the hydrogen breath test work?

In humans with Lactase Deficiency or Lactose Intolerance, the lactose reaches the colon, where it is metabolized by bacteria. This process produces gases, which triggers various symptoms and discomfort. One of the gases produced is hydrogen (H2). This gas is rapidly absorbed by the mucous membrane of the intestine, transported to the lungs, and then exhaled. As a result, elevated hydrogen levels in the exhaled air indicate a lactase deficiency. If sufficient lactase were present, lactose would not make it to the colon. In this case, the hydrogen levels would be the same before and after consuming the lactose.

Other diagnostic methods

Another possible way to diagnose Lactose Intolerance is the lactose tolerance test. In this test, lactose is also consumed and then blood is drawn at regular intervals. If sufficient lactase is present in the intestinal tract, it splits the lactose into galactose and glucose, and these are absorbed into the blood. The blood glucose level then increases. In the case of a Lactose Intolerance, the blood glucose would remain below a certain value.

A genetic test can also determine primary Lactose Intolerance, but not secondary Lactose Intolerance.

Both the genetic test and lactose tolerance test provide less meaningful results than the hydrogen breath test. If the symptoms of a Lactose Intolerance are present with a diet containing lactose (milk sugar), most doctors will opt to diagnose following a hydrogen breath test.

Further reading:

What is Lactose Intolerance?

Symptoms of Lactose Intolerance?

Treatment and therapy for Lactose Intolerance?