From the Guidelines
Lactose intolerance can be most accurately diagnosed using the hydrogen breath test, which measures hydrogen levels in breath after consuming lactose, as this method is considered the gold standard and has been shown to be superior to lactose tolerance tests in terms of sensitivity and specificity 1. The hydrogen breath test is a non-invasive and relatively easy to perform method that involves ingestion of 25–50 g lactose dissolved in 200–500 ml water after an overnight fast, with end expiratory breath samples taken at 15–30 minute intervals for three hours. A rise of hydrogen concentration from basal levels by more than 20 parts per million is compatible with a positive diagnosis. Some of the key methods for diagnosing lactose intolerance include:
- Hydrogen breath test: This is the most widely used method and is considered the gold standard for diagnosing lactose intolerance 1.
- Lactose tolerance test: This test measures blood glucose levels after lactose consumption, with minimal rise indicating intolerance.
- Stool acidity tests: These tests are useful for infants and children, measuring acid levels in stool caused by undigested lactose.
- Genetic testing: This can identify lactase persistence mutations, though it doesn't confirm symptoms.
- Elimination diets: These involve removing lactose-containing foods for 2-4 weeks, then reintroducing them to observe symptom recurrence. It's worth noting that patient reports of lactose intolerance relate poorly to objective evidence and cannot be relied upon, therefore, a breath hydrogen test for lactose malabsorption should be performed on patients who are regular consumers of more than 0.5 pint (280 ml) of milk or equivalent dairy products, especially if they come from a racial group with a high incidence of lactose malabsorption 1. Additionally, a recent meta-analysis of epidemiological data reported that 68% (95% CI 64% to 72%) of the world’s population are lactase-deficient, and this approaches 100% in the Han Chinese population, highlighting the importance of considering lactose intolerance in patients with symptoms of malabsorption 1.
From the Research
Diagnostic Methods for Lactose Intolerance
The diagnosis of lactose intolerance can be challenging, but several tests are available to help identify the condition. Some of the methods used to diagnose lactose intolerance include:
- Genetic test: This test checks for the presence of a gene that codes for lactase, the enzyme responsible for breaking down lactose 2.
- Hydrogen breath test (HBT): This is a non-invasive test that measures the amount of hydrogen in the breath after consuming lactose. High levels of hydrogen indicate that lactose is not being properly absorbed 2, 3, 4.
- Quick lactase test: This test measures the level of lactase enzyme in the small intestine 2.
- Lactose tolerance test: This test measures the body's ability to absorb lactose by checking blood sugar levels after consuming lactose 2, 3, 5.
Comparison of Diagnostic Tests
Studies have compared the accuracy of different diagnostic tests for lactose intolerance. For example, one study found that the hydrogen breath test was more sensitive and specific than the lactose tolerance test 3. Another study found that new criteria for interpreting the hydrogen breath test results were more accurate than conventional criteria 4.
Clinical Practice
In clinical practice, the choice of diagnostic test may depend on the individual patient's symptoms and medical history. The hydrogen breath test is often used as a first-line test due to its non-invasive nature and high sensitivity and specificity 2. Other tests, such as the lactose tolerance test, may be used to confirm the diagnosis or to monitor the patient's response to treatment 5.