Diagnosis of lactose intolerance

Hydrogen breath test (also known as HBT or H2 breath test) – standard test:

breathtestAt your doctor’s surgery you will be given a glass of pure lactose (depending on country between 20g and 50g; 25g seem to be the best amount of lactose) and will need to drink it on an empty stomach. Afterwards readings will be taken every half hour for two hours or more. This will show whether the lactose is being broken down in the intestine. If the diagnosis is positive, the typical symptoms of lactose intolerance will also appear. This test has a hit ratio of nearly 100% and is therefore classified as sufficiently accurate. Research has shown that genetically caused lactose intolerance correlates 100% with the breath test. But a positive breath test does not mean that the lactose intolerance is caused by a genetic defect(2)!

You can find a more detailed description of the hydrogen breath test here...

There are also non-responders who don’t produce any H2. But if strong bloating, abdominal cramps, diarrhea and other symptoms during the breath test on, is a lactose intolerance very likely.

The 13C breath test

Alternatively you can make a so-called 13C breath test. The C stands for carbon. Here you’re also drinking a lactose solution, but the carbon atom is "marked" in this lactose. The measurement is then the 13CO2 concentration in the breath, so the CO2 that was formed with this labeled carbon by bacteria in the intestine. In practice this test is hardly used. Usually for cost reasons, or because the corresponding measurement devices do not exist.

Blood glucose test:

A glass of pure lactose is given to drink under medical supervision. The following lab-test of the blood glucose levels will show whether the lactose has been broken down into glucose and galactose, which will then raise the blood glucose levels. This test should be carried out as an additional test at the same time as the hydrogen breath test (optional).

Genetic test for lactose intolerance:

iStock_mikroskopA medical professional will either conduct a mouth swab test or a blood test. The sample will be sent to a lab for genetic testing and will be evaluated there. This test is only able to detect lactose intolerance of the genetic type. If lactose intolerance exists due to the damage of the intestine, then this particular test will give a “false” result. This test is mostly only used in specific cases.


In very rare cases a tissue sample will be removed from the small intestine in order to test for lactose intolerance.

Exclusion diet:

If symptoms appear to disappear after several days of strictly avoiding lactose (this means all dairy products and processed foods that contain lactose), then the presence of lactose intolerance is possible.
This test is unfortunately very imprecise, and requires a high degree of expertise to enable identification of all products containing hidden lactose! For this reason this test cannot be recommended!

Exposure test:

The person drinks a glass of milk on an empty stomach (best done in the morning). If symptoms appear within between a couple of minutes to several hours (nausea, diarrhoea, stomach cramps, cold sweat...), then it is an indication of possible lactose intolerance.
Here, too, the diagnosis is not definitive and the test is therefore not to be recommended!


Electric currents in the body are measured with the help of an electrode, in order to draw conclusions regarding the person’s current condition. This method is not recognised and we highly advise you to have a breath test (or any other medically approved test) done instead by a medical professional!

IgG test:

This test measures the immune reaction of the body (Immunoglobuline G). This test is unsuitable for the diagnosis of lactose intolerance, dietary fructose intolerance (fructose malabsorption) and histamine intolerance.

Tests for the diagnosis of lactose intolerance should without exception be undertaken under medical supervision.

Sources include:
(1)Tuula H, Marteau P, Korpela R. (2000): Lactose Intolerance, J of the American College of Nutrition, Vol. 19, No. 2, 165S-175 S, 2000
(2) Marcin Krawczyk, Malgorzata Wolska, Stephanie Schwartz, et al); "Concordance of Genetic and Breath Tests for Lactose Intolerance in a Tertiary Referral Centre", J Gastrointestin Liver Dis, June 2008 Vol.17 No 2, 135-139
(3)Maximilian Ledochowski (2008): H2-Atemteste, verlag Ledochiwski, 1. Auflage


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