From the Guidelines
To diagnose lactose intolerance, the lactose hydrogen breath test is the most widely used and recommended method, due to its ease of performance, non-invasiveness, and relatively high sensitivity and specificity, as noted in the guidelines for the investigation of chronic diarrhoea 1. When performing the lactose hydrogen breath test, the procedure 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 1.
- A rise of hydrogen concentration from basal levels by more than 20 parts per million is compatible with a positive diagnosis.
- However, due to a false negative rate of up to 25%, a negative result does not exclude the diagnosis and hence a trial of a lactose free diet should be considered if the diagnosis is still suspected 1. Key points to consider when checking for lactose intolerance include:
- The lactose hydrogen breath test is superior to lactose tolerance tests and has similar sensitivity and specificity to the mucosal lactase assay 1.
- Other methods, such as lactose tolerance tests measuring serum glucose or galactose, and assay of mucosal lactase, are also available but may not be as practical or accurate 1.
- A trial of a lactose-free diet can be a useful diagnostic tool, especially if the hydrogen breath test is negative but symptoms persist 1.
From the Research
Diagnosis of Lactose Intolerance
To check for lactose intolerance, several methods can be used, including:
- Genetic test
- Hydrogen breath test (HBT)
- Quick lactase test
- Lactose tolerance test 2 The HBT is the most commonly used method due to its non-invasive nature, low cost, and high sensitivity and specificity.
Hydrogen Breath Test
The HBT involves measuring the amount of hydrogen in a patient's breath after consuming lactose. A positive result is typically indicated by an increase in hydrogen levels above a certain threshold, such as 20 parts per million (ppm) 3, 4. The test can be performed with different sampling schedules, including two-sample or three-sample tests, with the three-sample test being more accurate 3.
Other Diagnostic Methods
Other methods, such as the lactose tolerance test, can also be used to diagnose lactose intolerance. This test measures the patient's blood sugar levels after consuming lactose, with a failure to rise above a certain level indicating lactose malabsorption 5. The quick lactase test is another option, although its use is less common.
Interpretation of Test Results
The interpretation of test results is crucial in diagnosing lactose intolerance. For example, a positive HBT result can indicate lactose malabsorption, while a negative result may not necessarily rule out the condition 4. The use of new criteria, such as a breath hydrogen excretion value > 6 ppm 6 hours after carbohydrate load, can improve the accuracy of the HBT 6.
Additional Considerations
In addition to the HBT, other factors can be considered when diagnosing lactose intolerance, such as the patient's symptoms and medical history. The use of methane measurements can also provide additional information, as some patients may produce methane instead of hydrogen after consuming lactose 4.