Letzte Aktualisierung am 7. December 2023 von Dr. Michael Zechmann-Khreis
If you suspect that you suffer from lactose intolerance, you should keep a food and symptom diary . This makes it easier for the attending physician to narrow down the symptoms.
You can try it yourself, with caution of course. If a consistent diet without lactose (i.e. without dairy products and finished products containing lactose) for several days results in the disappearance of symptoms, lactose intolerance is likely. However, you need a great deal of knowledge about the lactose content of foods for such a self-test. Alternatively, you can drink a glass of milk on an empty stomach. If you get symptoms within about two hours (including stomach rumbling), you are probably lactose intolerant. You should then eat a normal diet and keep a symptom diary for about 1-2 weeks.
Self-tests are generally not recommended, but can confirm an initial suspicion.
Lactose intolerance diagnosis: the H2 breath test
The best diagnostic method and current gold standard is an H 2 –breath test at the doctor’s. You drink a test solution (25g lactose dissolved in warm water) on an empty stomach. You then blow into a breath measuring device at defined intervals, which measures the hydrogen content (hydrogen is chemically H2) in the air you breathe. The whole procedure takes about 2-3 hours. If the lactose is not properly metabolized by your body, bacteria in the large intestine produce hydrogen. This hydrogen then passes through the blood into the air we breathe and can be measured there. This creates a measurement curve which the doctor can use to determine or rule out lactose intolerance. The test for fructose intolerance is similar and is described in more detail here.
In addition to these measured values, the symptoms that occur during the test are also important for diagnosis. This is because not everyone reacts in the same way and, above all, some people have bacteria that do not produce hydrogen or immediately consume it themselves and produce methane in the process. Such patients are called non-responders. Therefore, the methane content of the breath should also be measured, but this practically never happens, as there are almost no methane measuring devices in medical practices. A diagnosis is nevertheless possible, as there are symptoms in the test. A blood analysis can also be carried out (see below).
The 13C breath test
Alternatively, you can take a so-called 13C breath test. The C stands for carbon. This also involves drinking a lactose solution, but one carbon atom in this lactose is “marked”. The 13CO2 concentrationin the breath is then measured, i.e. theCO2 formed by the bacteria in the intestine with this labeled carbon. In practice, however, 13C breath testsare rarely used. Mostly for cost reasons or because the appropriate measuring devices are not available.
However, the following still applies to non-responders: If severe flatulence, abdominal cramps, diarrhea and similar symptoms occur during the breath test, lactose intolerance is very likely.
Preparation for the breath test
It is advisable not to make any other appointments on the day of the test. If the test is positive, you will continue to have more or less severe symptoms for a few hours.
Further diagnostic options for lactose intolerance
Blood sugar test (lactose tolerance test)
A glass of lactose solution is drunk under medical supervision. The subsequent laboratory measurements of the blood sugar level show whether the milk sugar is broken down into glucose and galactose, which increases the blood sugar level. This test can be carried out as an additional test at the same time as the H2 breath test (optional).
In very rare cases, a tissue sample can be taken from the small intestine and tested for lactose intolerance. This is usually only done if a gastroscopy is performed for other reasons.
Diagnostic procedures for lactose intolerance that are not recommended
The doctor will either take a cheek swab or draw blood. The sample is then sent to the genetic laboratory where it is analyzed. This test can theoretically only detect genetic lactose intolerance (primary form). If there is a secondary lactose intolerance, the test will give a “false” result. But beware: there are several gene segments that are responsible for lactase production. The test does not examine all sections, and even if it did, there is a possibility that your body still produces enough lactase despite a “positive” result. In short, genetic testing is not a safe method and should not be used.
Electrodes are used to measure electrical currents in the body in order to draw conclusions about the patient’s condition. This method is not recognized and it is strongly recommended to have a breath test (or other conventional medical test) carried out!
This test measures an immune reaction of the body (immunoglobulin G). These tests are not suitable for detecting lactose intolerance, fructose malabsorption or histamine intolerance.
The tests for the diagnosis of lactose intolerance should be carried out under medical supervision without exception. H2 breath tests for home use should not be used, as the bags or tubes in which the breath is collected are not tight enough to hold the hydrogen until it is analyzed in the laboratory. Therefore, these tests may give false results.
Sources and others
(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 Center”, J Gastrointestin Liver Dis, June 2008 Vol.17 No 2, 135-139
(3) Vogelreuter A., “Food intolerances”, Wissenschaftliche Verlagsgesellschaft Stuttgart, 2012