Letzte Aktualisierung am 5. September 2024 von Dr. Michael Zechmann-Khreis
Lactose intolerance refers exclusively to the intolerance of the milk sugar lactose. However, it does not identify the exact cause of this intolerance. However, as the causes are crucial for successful treatment, medical clarification is essential. But how does the diagnosis of lactose intolerance work? What diagnostic methods are there and are they reliable? We have summarized all this for you in this article.
The symptom diary
If lactose intolerance is suspected, it is advisable first of all to keep a food and symptom diary first of all. This helps the doctor treating you to better classify the symptoms and make a specific diagnosis. There are forms available online for this purpose, as well as small booklets and larger books that you can use to fill in. These diaries should be kept for 7 to 14 days.
Lactose intolerance diagnosis: the H2 breath test
The H2 breath test is considered the best diagnostic method and the current gold standard for detecting lactose intolerance. H2 stands for hydrogen. In this test, you drink a test solution on an empty stomach. For adults, it is recommended to dissolve 25g of lactose in 250ml of warm water. In the past, 50g was recommended, but this corresponds to about one liter of milk and can also trigger symptoms in people without lactose intolerance. Unfortunately, this value is sometimes still published and used by some doctors. For children, 1g of lactose per kg of body weight is recommended, with a maximum of 25g. 1
After taking the test solution, you blow into a breath meter at regular intervals, usually every 30 minutes, which measures the hydrogen content in the air you breathe. The entire procedure takes about 3-4 hours. If the lactose is not properly metabolized, bacteria in the large intestine produce hydrogen, which passes through the blood into the breath and can be measured there. Based on the measurement curve, the doctor can determine or rule out lactose intolerance. The test for fructose intolerance is similar and is described in more detail in this article.
In addition to the measured values, the symptoms occurring during the test are also important for the diagnosis. Not everyone reacts in the same way, and around 10% of people have bacteria that do not produce hydrogen or immediately consume it themselves, producing methane. These patients are called non-responders. Therefore, the methane content of the breath should also be measured, but this is rarely done as there are hardly any methane measuring devices in surgeries. A diagnosis is nevertheless possible by observing the symptoms for half a day. If symptoms such as abdominal pain (lower abdomen), flatulence and diarrhea occur, intolerance can be assumed.
H2 tests for at home
Breath H2 samples are stable for six hours at room temperature. If the sample has to be kept for longer, it must be stored at -20 °C, as a third of the hydrogen will escape from the container within a few days2. This is not feasible for a self-test at home by post, which is why such home tests are not recommended.
Other lactose intolerance tests that are not recommended
The genetic test
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 only detect a genetic predisposition to age-related lactose tolerance. However, it says nothing about whether you actually develop an intolerance. This test alone is therefore not useful, but your doctor can also use the test to obtain information on other diagnoses/therapy approaches.
Small intestine biopsy
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. However, the informative value with regard to intolerance is very limited, which is why this method is no longer recommended.
The 13C breath test
Alternatively, a so-called 13C breath testcould be carried out to diagnose lactose intolerance. The C stands for carbon. This also involves drinking a lactose solution, but one carbon atom in this lactose is “marked”. The 13CO2concentration in the breath is then measured, i.e. theCO2 formed by the bacteria in the intestine with this labeled carbon. 3 In practice, however, 13C breath testsare rarely used. Mostly for cost reasons or because the appropriate measuring devices are not available. In addition, the H2 test is simpler, cheaper and sufficient as a diagnostic method.
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 diagnosis of lactose intolerance may give false results due to other internal problems and is therefore no longer recommended.
Bioresonance, hair analysis and co
There are some esoteric diagnostic methods such as bioresonance, hair analysis, spit analysis, laying on of hands or scrying. All these methods lack any scientific basis and it is strongly advised not to use them for diagnosis.
IgG test
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 .
Sources
1 Satta, P. U. et al. H2-breath testing for carbohydrate malabsorption . Aliment. Pharmacol. Ther. 29, 14-18 (2009).
2. Corazza, G. R. et al. Methodology of the H2 breath test .
I. Collection and storage for gas measurement. Ital.
J. Gastroenterol. 22, 200-204 (1990).
3. Hiele, M. et al. 13CO2 breath test using naturally 13C-enriched lactose for detection of lactase deficiency in patients with gastrointestinal symptoms . J. Lab.
Clin.
Med. 112, 193-200 (1988).
